Repeated Bun v1.3.5 segfaults -- 78 crashes, root cause identified (Windows + WSL)

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/21869
2. https://github.com/anthropics/claude-code/issues/21620
3. https://github.com/anthropics/claude-code/issues/21469

This issue will be automatically closed as a duplicate in 3 days.

• If your issue is a duplicate, please close it and 👍 the existing issue instead
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🤖 Generated with Claude Code

Dump Analysis Follow-Up: 27 Full Memory Dumps (Feb 4-5, 2026)

This follows the consolidation report that condensed 85 individual crash report comments into a structured analysis identifying 3 crash families and a suspected N-API race condition root cause. Since that report, we captured 27 full-memory dumps via ProcDump and analyzed them with cdb (WinDbg command-line debugger). The new data confirms a single root cause across four crash families and provides disassembly-level evidence for the corruption mechanism.

Symbol disclaimer: claude.exe ships without debug symbols. All function names in stack traces (e.g., uv_tty_get_vterm_state, uv_getnameinfo, simdutf::get_active_implementation) are nearest-export-symbol artifacts -- cdb resolves addresses to the closest exported function name. The actual code at those offsets is Bun/JSC internal code, NOT libuv TTY code or simdutf. Bun developers should use the RVA offsets (e.g., +0x11d3a8) to locate the real code in a symbolicated build.

Environment

• OS: Windows 11 x64 Build 26200
• CPU: Intel Core i9-14900HX (32 logical processors)
• Claude Code: v2.1.31 (26 dumps), v2.1.32 (1 dump)
• Embedded Bun: v1.3.5
• Capture tool: ProcDump (full memory dumps, -ma flag)

Family Distribution (27 dumps)

| Family | Count | % | Exception | Mechanism |
|--------|-------|---|-----------|-----------|
| F2: Main Thread / JSC GC | 22 | 81.5% | C0000005 (Access Violation) | Corrupted vtable indirect call; NaN-boxing sentinel fault addresses |
| F4: FAST_FAIL | 3 | 11.1% | C0000409 | Bun internal corruption detection -> __fastfail(7) |
| F5: Partial Pointer | 1 | 3.7% | C0000005 (Access Violation) | Partial pointer corruption (0x000001FF00000003) |
| F6: Heap Corruption | 1 | 3.7% | C0000374 | Windows heap manager detects double-free |
| F1: Worker Thread | 0 | 0% | -- | Not observed in this batch |

Process uptimes ranged from 35 seconds to 1 hour 13 minutes -- the crash is a race condition with no time threshold.

---

Key Finding 1: All Families Share One Code Path

Disassembly and stack analysis across F2, F4, and F6 show all three pass through the same code regions (symbol names are nearest-export artifacts; RVA offsets identify the actual code):

• F2 (segfault): napi_remove_async_cleanup_hook -> simdutf::get_active_implementation -> uv_tty_get_vterm_state+0x11d3a8 -> RIP = 0x7
• F4 (FAST_FAIL): node_module_register -> simdutf::get_active_implementation -> uv_tty_get_vterm_state -> uv_getnameinfo+0x5c029 (int 29h)
• F6 (heap corruption): uv_tty_get_vterm_state+0xd32e6 -> uv_getnameinfo+0x7968c -> RtlFreeHeap -> HEAP_FAILURE_SEGMENT_LFH_DOUBLE_FREE

The F2 crash site disassembly at uv_tty_get_vterm_state+0x11d3a8:

mov  rdx, r9           ; set up argument
call qword ptr [rcx]   ; indirect call through vtable pointer -> loads 0x7 into RIP

This is a C++ virtual function call or function-pointer dispatch. At crash time, [rcx] contains 0x7 -- a corrupted vtable entry from a freed object. The small value 0x7 is consistent with free-list metadata or a zeroed pointer that replaced the valid vtable when the GC reclaimed the object prematurely.

Register fingerprint across all F2 dumps: r12 = fffe000000000002 (NaN-boxed boolean true in JSC encoding), confirming crashes occur during active JS execution in the JSC interpreter loop -- not during startup or shutdown.

Thread state is identical across all families. Every dump shows:

• 7-9 threads in napi_unref_threadsafe_function -> RtlWaitOnAddress
• 4-8 threads in simdutf::get_active_implementation -> SleepConditionVariableSRW (worker pool)
• 4 libuv worker threads
• 1 thread running uv_run event loop inside napi_unref_threadsafe_function

The napi_unref thread count stabilizes at 7-9 regardless of total thread count (26-42), crash family, or process uptime.

---

Key Finding 2: FAST_FAIL Trigger Decoded

The consolidation report noted "silent crashes" where the process disappears without a crash dialog. This is now explained. Disassembly at the F4 crash site (uv_getnameinfo+0x5c029):

call    claude!uv_getnameinfo+0x67038              ; call validation function
test    byte ptr [claude!icudt73_dat+0x222d05c], 2 ; test a flag bit
je      skip_abort                                  ; if not set, skip
mov     ecx, 17h                                    ; load parameter 0x17
call    qword ptr [claude!icudt73_dat+0x1f06490]   ; call through function pointer
test    eax, eax                                    ; check return value
je      skip_abort                                  ; if zero (ok), skip
mov     ecx, 7                                      ; FAST_FAIL_FATAL_APP_EXIT
int     29h                                         ; __fastfail(7) -- process terminated

This is a two-stage validation sequence. Stage 1 calls a check function and tests a flag. Stage 2 calls through a function pointer and checks the result. If both indicate corruption, Bun fires __fastfail(7) (FAST_FAIL_FATAL_APP_EXIT) -- the Windows equivalent of abort().

The int 29h instruction raises a non-continuable second-chance exception (C0000409) that bypasses SEH entirely. The process is terminated by the kernel without invoking any exception handlers or crash reporters. This is why the process "just disappears" -- Bun detects corruption, calls abort, and the kernel kills the process before any crash UI can appear.

F4 is the same corruption as F2, detected by a different code path. The race is between: (a) dereferencing the corrupted pointer directly (produces F2 segfault at 0x7), and (b) Bun's validation check catching the invalid state first (produces F4 FAST_FAIL). Which fires first depends on CPU scheduling.

---

Key Finding 3: Double-Free Confirmed

The F6 dump provides the most direct evidence of the corruption mechanism. The !heap -s output:

Error type:    HEAP_FAILURE_SEGMENT_LFH_DOUBLE_FREE
Details:       The heap detected that the current free operation
               is attempting to free a block which is already free.
Error address: 0000021551efa6e0

This is textbook double-free. The N-API race condition causes two code paths to free the same memory:

1. napi_remove_async_cleanup_hook frees the async resource
2. JSC GC sweep later tries to free the same backing memory (or vice versa)

The crash stack passes through the same code regions as F2 and F4:

ntdll!RtlFreeHeap+0x231
claude!uv_getnameinfo+0x7968c       (Bun internal code)
claude!uv_tty_get_vterm_state+0xd32e6  (same region as F2/F4)
0x0000021510363156                   (JIT-compiled code)

The Windows heap manager caught the double-free during RtlFreeHeap before the corruption could propagate to a segfault.

---

Unified Model

All four crash families are the same bug detected by four different mechanisms:

1. F2 (81.5%): CPU catches invalid memory access when code dereferences a corrupted pointer
2. F4 (11.1%): Bun's internal validation detects corruption before the dereference
3. F5 (3.7%): Corrupted pointer lands in an unusual address range (0x000001FF00000003 -- partial pointer corruption)
4. F6 (3.7%): Windows heap manager detects double-free during RtlFreeHeap

The underlying corruption is a race condition between napi_remove_async_cleanup_hook and concurrent napi_unref_threadsafe_function operations. When cleanup hook removal and threadsafe function operations interleave, an object gets freed while still referenced (or freed twice). Fix the N-API lifecycle race and all four families should disappear.

---

Open Questions

• F1 (Worker Thread Cleanup) was absent from all 27 dumps. It may be rare (a 27-sample batch has a 25% chance of missing a 5%-frequency event), workload-dependent, or possibly misclassified in the earlier analysis which had only 5 dumps.
• ProcDump capture rate for FAST_FAIL is unknown. __fastfail bypasses SEH, so ProcDump must catch it as an unhandled exception. Our 11.1% F4 rate is likely a lower bound -- some FAST_FAIL crashes may not produce dumps.
• Exact identity of the corrupted object is unknown without debug symbols. We can see the vtable pointer was corrupted to 0x7, but identifying which C++ class requires a symbolicated build or a debug build reproduction.
• v2.1.32 (1 dump) shows identical crash behavior to v2.1.31. The v2.1.32 changelog contains no changes to Bun version or N-API handling. The crash signature (fault address 0x7, F2 family, r12 = fffe000000000002) is indistinguishable from v2.1.31 dumps.

---

<details>
<summary>Full Dump Inventory (27 dumps)</summary>

| # | Dump File | Uptime | Threads | Fault Address | AV Type | Family | Version |
|---|-----------|--------|---------|---------------|---------|--------|---------|
| 1 | 260204_094147 | 3:47 | 38 | 0x7 | Execute | F2 | 2.1.31 |
| 2 | 260204_095059 | 4:52 | 35 | FAST_FAIL (int 29h) | C0000409 | F4 | 2.1.31 |
| 3 | 260204_095537 | 4:21 | 36 | 0xFFFFFFFFFFFFFFFE | Read | F2 | 2.1.31 |
| 4 | 260204_095936 | 1:51 | 37 | 0xA | Read | F2 | 2.1.31 |
| 5 | 260204_103149 | 24:03 | 34 | 0xFFFFFFFFFFFFFFFF | Read | F2 | 2.1.31 |
| 6 | 260205_000334 | 1:40 | 34 | 0xFFFFFFFFFFFFFFFF | Read | F2 | 2.1.31 |
| 7 | 260205_001841 | 13:46 | 32 | 0x0 | Read | F2 | 2.1.31 |
| 8 | 260205_002154 | 3:02 | 38 | 0xFFFFFFFFFFFFFFFF | Read | F2 | 2.1.31 |
| 9 | 260205_092138 | 6:00 | 38 | 0x6 | Read | F2 | 2.1.31 |
| 10 | 260205_092443 | 2:44 | 39 | FAST_FAIL (int 29h) | C0000409 | F4 | 2.1.31 |
| 11 | 260205_100709 | 42:18 | 34 | 0xFFFFFFFFFFFFFFFE | Read | F2 | 2.1.31 |
| 12 | 260205_102340 | 12:47 | 30 | 0x000001FF00000003 | Read | F5 | 2.1.31 |
| 13 | 260205_103137 | 7:43 | 35 | 0xFFFFFFFFFFFFFFFF | Read | F2 | 2.1.31 |
| 14 | 260205_104800 | 11:59 | 40 | 0x7 | Execute | F2 | 2.1.31 |
| 15 | 260205_105502 | 13:52 | 32 | 0xFFFFFFFFFFFFFFFE | Read | F2 | 2.1.31 |
| 16 | 260205_105547 | 0:35 | 40 | FAST_FAIL (int 29h) | C0000409 | F4 | 2.1.31 |
| 17 | 260205_105736 | 0:49 | 38 | 0xFFFFFFFFFFFFFFFE | Read | F2 | 2.1.31 |
| 18 | 260205_110114 | 5:15 | 33 | Heap corruption (C0000374) | RtlReportFatalFailure | F6 | 2.1.31 |
| 19 | 260205_111011 | 8:33 | 34 | 0xFFFFFFFFFFFFFFFF | Read | F2 | 2.1.31 |
| 20 | 260205_112647 | 26:14 | 28 | 0xFFFFFFFFFFFFFFFF | Read | F2 | 2.1.31 |
| 21 | 260205_113329 | 1:13:23 | 26 | 0xFFFFFFFFFFFFFFFE | Read | F2 | 2.1.31 |
| 22 | 260205_115948 | 32:47 | 28 | 0x7 | Execute | F2 | 2.1.31 |
| 23 | 260205_120718 | 30:12 | 29 | 0x7 | Execute | F2 | 2.1.31 |
| 24 | 260205_121446 | 7:13 | 32 | 0xFFFFFFFFFFFFFFFE | Read | F2 | 2.1.31 |
| 25 | 260205_122153 | 5:20 | 37 | 0xFFFFFFFFFFFFFFFF | Read | F2 | 2.1.31 |
| 26 | 260205_132149 | 59:48 | 34 | 0x0 | Read | F2 | 2.1.31 |
| 27 | 260205_133922 | 11:04 | 42 | 0x7 | Execute | F2 | 2.1.32 |

Uptime format is minutes:seconds except dump 21 which is hours:minutes:seconds.

</details>

<details>
<summary>Disassembly Evidence</summary>

1. F2: Vtable corruption (crash site)

From dump claude.exe_260205_115948.dmp, disassembly at claude!uv_tty_get_vterm_state+0x11d3a8:

; This is the crash instruction. rcx points to an object whose vtable
; has been corrupted. [rcx] loads 0x7 into RIP -> ACCESS_VIOLATION (execute).
; The function names are nearest-export-symbol artifacts -- this is actually
; Bun/JSC internal code, NOT libuv TTY code.

mov  rdx, r9           ; argument setup
call qword ptr [rcx]   ; indirect call through vtable -> RIP = 0x7

Register state at crash:

rax=00000150e60adc40  rbx=fffe000000000000  rcx=000000a301d8c200
rdx=00000150e60adc40  rsi=000002b508826718  rdi=00000150e60adc40
r8=000000000000001e   r9=000002b50994ba40   r10=0000000000000018
r11=000000a301d8c200  r12=fffe000000000002  r13=000000000000000a
r14=0000000000000001  r15=000002b508830000

Note: r12 = fffe000000000002 is a NaN-boxed boolean true in JSC's encoding scheme. This value is consistent across all F2 dumps, confirming the crash occurs during active JavaScript execution in the JSC interpreter loop.

2. F4: FAST_FAIL trigger (validation and abort sequence)

From dump claude.exe_260204_095059.dmp, disassembly at claude!uv_getnameinfo+0x5c029 (obtained via ub -- unassemble backward):

; Two-stage validation check. If corruption is detected, Bun calls
; __fastfail(7) which terminates the process immediately via kernel,
; bypassing SEH and crash reporters. This explains "silent crashes."

call    claude!uv_getnameinfo+0x67038              ; Stage 1: validation function
test    byte ptr [claude!icudt73_dat+0x222d05c], 2 ; test corruption flag
je      claude!uv_getnameinfo+0x5c03f              ; if clear, skip abort

mov     ecx, 17h                                    ; parameter 0x17 (23)
call    qword ptr [claude!icudt73_dat+0x1f06490]   ; Stage 2: secondary check
test    eax, eax                                    ; check result
je      claude!uv_getnameinfo+0x5c02b              ; if zero, skip abort

mov     ecx, 7                    ; FAST_FAIL subcode: FAST_FAIL_FATAL_APP_EXIT
int     29h                       ; __fastfail(7) -- kernel terminates process

3. F6: Heap analysis (double-free detection)

From dump claude.exe_260205_110114.dmp, !heap -s output:

HEAP_FAILURE_BLOCK_NOT_BUSY at 0000021551efa6e0

Error type:    HEAP_FAILURE_SEGMENT_LFH_DOUBLE_FREE
Details:       The heap detected that the current free operation
               is attempting to free a block which is already free.
Error address: 0000021551efa6e0

Stack at failure:
  ntdll!RtlFreeHeap+0x231
  claude!uv_getnameinfo+0x7968c        ; Bun internal (symbol is artifact)
  claude!uv_tty_get_vterm_state+0xd32e6 ; Same code region as F2/F4
  0x0000021510363156                    ; JIT-compiled code

The double-free confirms the race condition: one code path (N-API cleanup) frees the resource, then another code path (JSC GC sweep) attempts to free the same backing memory.

</details>

<details>
<summary>Analysis Methodology</summary>

Capture:

• ProcDump configured with -ma flag for full memory dumps
• Monitored claude.exe for unhandled exceptions
• 27 dumps captured over Feb 4-5, 2026 during normal Claude Code usage

Analysis tools:

• cdbX64.exe from WinDbg Store package (command-line debugger)
• Analysis commands: .exr -1 (exception record), !analyze -v (verbose analysis), ~*kn (all thread stacks with frame numbers), !heap -s (heap summary), ub (unassemble backward from address), dps (display pointer-sized values with symbols)

Process:

1. Batch extraction via PowerShell script (analyze-all.ps1) -- extracted exception code, fault address, AV type, process uptime, thread count, and Claude Code version from all 27 dumps
2. Classification against known families from the consolidation report
3. Three detailed deep-dive analyses: one F2 dump (115948), one F4 dump (095059), one F6 dump (110114)
4. Cross-family comparison of thread state (~*kn), register state, and code paths

Limitations:

• No debug symbols for claude.exe -- all function names are nearest-export-symbol artifacts
• Stack unwinding is impaired by JSC's mixed native/JS frame layout
• JIT-compiled code regions cannot be disassembled meaningfully (they change per execution)

</details>

---

Note

This comment was written by Claude (Opus 4.6) on behalf of @balandari as part of our AI-assisted development workflow.

First npm/Node.js Crash Dump Captured

After switching from Bun to npm (Node.js v22.22.0) to escape the NaN-boxing crashes, we've now captured the first Node.js crash. Different runtime, different crash mechanism.

Environment

• Runtime: Node.js v22.22.0 (npm, not Bun)
• Claude Code version: Current (npm-based)
• OS: Windows 11
• Process uptime: 13 minutes 54 seconds
• Context at crash: ~80% context window, orchestrator was mid-analysis after running tests (heavy thinking)
• ProcDump config: procdump -ma -e -w node.exe

Exception

• Code: 0xC0000005 (Access Violation -- INVALID_POINTER_WRITE)
• Faulting instruction: mov dword ptr [rdi], ebx at 0x0000033d9b1e2024
• Write target: 0x0000000000011a18 (near-null, unmapped)

Registers

rax=00000000000119a8  rbx=00000000000119b0  rcx=0000000000000000
rdx=000000000012313c  rsi=0000036654f60111  rdi=0000000000011a18
rip=0000033d9b1e2024  rsp=00000009183fc2a0  rbp=00000009183fc348
 r8=0000000000011a28   r9=00000000ffffffff  r10=0000033d9b1e1958
r11=00000000000119a8  r12=0000000000000000  r13=0000013316600080
r14=0000000000000000  r15=0000000000000000

Multiple registers (rax, rbx, rdi, r8, r11) contain similarly low addresses (0x119a8, 0x119b0, 0x11a18, 0x11a28) -- offsets from a null base object.

Call Stack (Key Frames)

ntdll!RtlUserThreadStart
kernel32!BaseThreadInitThunk
node+fa4780                          (Node.js entry)
node!node::Start+0x1e
node!node::SpinEventLoop+0x195       (event loop)
node!uv_run+0x3ef                    (libuv)
node!uv_pipe_pending_type+0x354      (pipe I/O callback)
node!node_api_throw_syntax_error+... (NAPI dispatch)
node!node::MakeCallback+0xf7         (native -> JS)
node!v8::Function::Call+0x134        (V8 call)
--- V8 JIT code zone ---
0x0000033d9b1e9f14  x9 frames        (recursive function, counter 12->5)
0x0000033d9b1e8d0c  x3 frames        (alternate JIT function)
0x0000033d9b1e2024  <-- CRASH        (null deref with ~72KB offset)

Analysis

Root cause: V8 JIT null object dereference during recursive execution.

The faulting IP is on the heap (JIT-compiled JavaScript). A recursive function with a decrementing counter (visible in args: 0xc, 0xb, 0xa... 0x5) was executing when it hit a null object reference. The ~72KB offset (0x11a18) suggests access to a field deep in a large object or indexed array that had been garbage collected while JIT code still held a stale reference.

The trigger path is: libuv pipe I/O -> NAPI callback -> V8 Function::Call -> JIT recursion -> null deref. This is Claude Code's IPC mechanism triggering JavaScript execution.

Comparison to Bun Crashes

| Characteristic | Bun crashes (30+ dumps) | This Node.js crash |
|---|---|---|
| Exception code | 0xC0000005 | 0xC0000005 |
| Pointer pattern | 0xfffe/0xffff NaN-boxed | 0x00011a18 near-null |
| Faulting location | Bun/Zig runtime | V8 JIT JavaScript |
| Root cause | NaN-boxed value misinterpreted as pointer | GC'd object still referenced by JIT code |
| Deep recursion | Not typically present | 9+ recursive frames |

This is a completely different crash family. No NaN-boxed pointers, no Zig runtime involvement. This is a V8 JIT compiler bug -- the generated code doesn't guard against a null reference during optimized recursive execution.

Implications

The npm switch eliminated the Bun NaN-boxing crashes (zero Bun crashes since switching), but Node.js/V8 has its own crash vector. Same symptom (unexpected termination during heavy usage at high context), different engine, different mechanism. The common factor across both runtimes appears to be Claude Code's usage pattern: sustained heavy computation with high context and active IPC.

Note

This comment was written by Claude (Opus 4.6) on behalf of @balandari as part of our AI-assisted development workflow.

Additional Data: npm ~80% Context Crash Pattern

Adding another data point to the Node.js crash pattern documented in my Feb 6 comment.

New incident (Feb 10, 2026):

• Runtime: Node.js v22.22.0 (npm install), Claude Code 2.1.37
• Trigger: Running /analyze (heavy multi-file analysis) with context at ~80%+
• Result: Session crashed to command prompt
• Additional failure: On restart, hit a new error -- SyntaxError: Too many arguments in function call (only 65535 allowed) at cli.js:2026 during ESM module compilation. Restart failed repeatedly before eventually succeeding. Filed separately as #24874.

Pattern strengthening: This is now the second documented npm/Node.js crash at ~80% context during heavy workload. The common factors:

• npm version (not native/Bun)
• Node.js v22.22.0
• Context window at ~80%+
• Heavy computation (orchestrator analysis, multi-file operations)
• Windows x64

The restart failure (#24874) appears to be a secondary issue -- the bundled cli.js hitting a V8 bytecode compilation limit, possibly influenced by system state after the primary crash.

Note

This comment was written by Claude (Opus 4.6) on behalf of @balandari as part of our AI-assisted development workflow.

ProcDump Analysis -- 5 Full Dumps on Canary v1.3.9-canary.51 (Windows x64)

Five crashes within 22 minutes, all captured with ProcDump (-e 1 -ma). First canary dump analysis with full memory.

Triage Results

| Dump | Family | Exception | Fault Address | Threads | Uptime |
|------|--------|-----------|---------------|---------|--------|
| 100738 | F4 | c0000409 (FAST_FAIL) | n/a (int 29h) | 40 | 5:46 |
| 102058 | F4 | c0000409 (FAST_FAIL) | n/a | 46 | 12:54 |
| 102303 | F2 | c0000005 | 0xFFFFFFFFFFFFFFFF (read) | 50 | 1:56 |
| 102516 | F2 | c0000005 | 0xFFFFFFFFFFFFFFFF (read) | 44 | 1:41 |
| 102945 | F2-new | c0000005 | 0x1CACC793F40 (execute) | 37 | 3:55 |

Distribution: F4 (FAST_FAIL) 40%, F2 (NaN-boxing) 40%, F2-variant (execute AV) 20%.

F4 Stack Trace -- N-API Cleanup Path Confirmed

Dump #1 (100738) stack trace via cdb:

claude!uv_getnameinfo+0x1ea909          <- int 29h (FAST_FAIL trigger)
claude!llhttp_should_keep_alive+0x12d87
claude!napi_close_callback_scope+0x89d3f
claude!napi_close_callback_scope+0x21527
claude!napi_close_callback_scope+0x204fe
claude!v8::Value::StrictEquals+0x336581
claude!v8::Value::StrictEquals+0x337183
0x0000020e82918413                      <- JIT-compiled code

Three frames through napi_close_callback_scope before the FAST_FAIL_FATAL_APP_EXIT (__fastfail(7)). Bun's internal corruption check fires during N-API callback scope cleanup. This supports the root cause identified in our previous dump analyses: N-API race condition during cleanup triggers use-after-free, Bun detects the corruption and aborts.

New Variant: Execute AV at Heap Address

Dump #5 (102945) -- a new crash pattern not seen in our previous 40+ dump analyses:

ExceptionAddress: 000001cacc793f40
ExceptionCode: c0000005 (Access violation)
Attempt to execute non-executable address 000001cacc793f40

The stack is completely trashed -- JSC NaN-boxed tagged values (0xFFFE0000000000A3, 0xFFFE0000000000006) mixed with heap pointers. This is a corrupted function pointer/vtable: JSC tried to call through a pointer that had been freed and reallocated as heap data. Different from the standard F2 NaN-boxing sentinel crashes -- those read from an obviously invalid address, this one tried to execute at a plausible heap address.

Crash Context and Memory Correlation

• First crash occurred at >50% conversation context usage, RSS 0.87GB
• After restart, subsequent crashes happened in under 2 minutes at 1.46-1.99GB RSS
• Orphaned claude.exe processes from previous crashes remained in memory (Windows crash handler doesn't reliably terminate the process)
• 5-7 orphaned processes accumulated ~4.5GB combined, creating a feedback loop: crashes leave orphans -> orphan memory pressure -> faster crashes -> more orphans

Orphaned Process Feedback Loop (Windows-Specific)

On Windows, when Bun crashes, the claude.exe process often isn't fully terminated. Closing the terminal window also doesn't reliably kill the child process. Each crash-and-restart cycle can leave an orphan holding hundreds of MB. Monitoring command:

Get-CimInstance Win32_Process | Where-Object {
    $_.ExecutablePath -eq 'C:\Users\Mike\.local\bin\claude.exe'
} | Sort-Object CreationDate |
Format-Table ProcessId, @{Label='RSS_MB';Expression={[math]::Round($_.WorkingSetSize/1MB,0)}}, CreationDate -AutoSize

During this session, 7 claude.exe processes were found when only 2 terminals were active. The 5 orphans consumed ~4.5GB combined. The oldest had been running 6+ hours at 1.16GB.

bun.report Links Broken for Canary Builds

None of the bun.report links resolve for canary v1.3.9-canary.51. They return either:

• {"error":"Could not find debug info for this version of Bun."}
• HTTP 502 Bad Gateway

Example links:

• https://bun.report/1.3.9/e_2d5628dbmgkgEuhogCA2u//Bvuy1+lD
• https://bun.report/1.3.9/e_2d5628dbmgkgEugogC_A2DD

Debug symbols are not published for canary builds. This means canary testers cannot use the standard Bun crash reporting path.

Crash Reports (Bun Panic Handler Output)

All five crashes on Bun Canary v1.3.9-canary.51 (d5628db2), Windows x64, claude.exe -c --dangerously-skip-permissions:

Crash 1 (0x7FF79A0A9B19 -- code-space):

Elapsed: 1442950ms | RSS: 0.87GB | Peak: 0.92GB | Commit: 1.25GB | Faults: 976223
Features: spawn(296) fetch(50) abort_signal(3)
bun.report/1.3.9/e_2d5628dbmgkgEuhogCA2u//Bvuy1+lD

Crash 2 (0xFFFFFFFFFFFFFFFF):

Elapsed: 117496ms | RSS: 1.46GB | Peak: 1.48GB | Commit: 1.20GB | Faults: 810441
Features: spawn(105) fetch(23)
bun.report/1.3.9/e_2d5628dbmgkgEugogC_A2DD

Crash 3 (0xFFFFFFFFFFFFFFFF):

Elapsed: 101135ms | RSS: 1.99GB | Peak: 2.00GB | Commit: 1.72GB | Faults: 1982513
Features: spawn(109) fetch(41) abort_signal(2)
bun.report/1.3.9/e_2d5628dbmgkgEuhogC__A2DD

Crash 4 (0x1CACC793F40 -- heap-space execute):

Elapsed: 235704ms | RSS: 1.32GB | Peak: 1.32GB | Commit: 1.05GB | Faults: 1529725
Features: spawn(122) fetch(37)
bun.report/1.3.9/e_2d5628dbmgkgEugogC_____________A20chsg7wzB

Summary

• Canary v1.3.9-canary.51 does not fix the crash. Same families (F2, F4), same root cause (N-API cleanup race condition), plus a new variant (execute AV at heap address).
• F4 (FAST_FAIL) is 40% of these crashes with napi_close_callback_scope directly in the call chain.
• Windows orphaned process accumulation creates a crash feedback loop.
• bun.report is broken for canary, so standard crash reporting doesn't work for canary testers.
• 5 full ProcDump captures available if the team wants the dump files.

Addendum: Two Additional Crashes (Same Session, Post-Restart)

Two more crashes after the original five, same canary build. CDB analysis on full ProcDump captures.

New evidence -- F2 shares the N-API cleanup path with F4:

Dump at 11:53 (F2, 0xFFFFFFFFFFFFFFFF read, 3 min uptime) produced a clean stack trace:

claude!bmalloc::Mutex::lockSlowCase+0x330860   <- corrupted pointer read (rdi=0x0B71530EFFBB8DB3)
claude!pas_system_heap_free
claude!napi_close_callback_scope
claude!uv_getnameinfo
KERNEL32!BaseThreadInitThunk
ntdll!RtlUserThreadStart

napi_close_callback_scope -> pas_system_heap_free -> bmalloc crash on garbage pointer. This is the same entry point as the F4 stack traces above, but F4 catches the corruption early (FAST_FAIL abort) while F2 lets it propagate to the allocator. Direct evidence that F2 and F4 are the same root cause with different detection timing.

Memory pressure ruled out as necessary condition:

System state at time of both crashes: 191.7GB total RAM, 167.5GB free (12.6% used), zero orphaned claude.exe processes. The orphan feedback loop documented above makes crashes worse, but is not required to trigger them. These crashes occur on a completely clean system.

Note

Embedded Bun version: v1.3.9-canary.51 (d5628db2). Latest stable Bun: v1.3.9. Canary is a pre-release of the same version family -- these crashes are not fixed in stable either.

This comment was written by Claude (Opus 4.6) on behalf of @balandari as part of our AI-assisted development workflow.

Cross-Runtime Analysis: Same Root Cause on Both Node.js and Bun

Connecting the dots between the Bun crash data (original report + canary analysis above) and the Node.js crash data (Feb 6 and Feb 11 comments).

Shared Crash Signatures Across Runtimes

| Indicator | Bun (v1.3.5, v1.3.9-canary.51) | Node.js (v22.22.0) |
|-----------|--------------------------------|---------------------|
| napi_close_callback_scope | In F2 and F4 stack traces | In crash path |
| uv_getnameinfo | Multiple dumps | In crash path |
| v8::Value::StrictEquals | Canary dumps 3, 4 | Node dump (Feb 10) |
| Fault address 0xFFFFFFFFFFFFFFFF | Dominant F2 pattern | Feb 10 dump |
| Exception | ACCESS_VIOLATION (c0000005) | ACCESS_VIOLATION (c0000005) |

Reframed Root Cause

The original report attributed this to Bun's N-API implementation. The Node.js crashes were documented separately as a potentially distinct issue. They aren't.

Both runtimes crash through the same N-API cleanup path (napi_close_callback_scope), produce the same freed-memory sentinel (0xFFFFFFFFFFFFFFFF) as the fault address, and involve the same V8-compatible API surface (v8::Value::StrictEquals). The native addon code loaded by Claude Code goes through N-API on either runtime, and the race condition between async cleanup and active threads causes use-after-free regardless of the underlying JS engine (JSC or V8).

This is not a Bun bug or a Node bug. It's a native addon lifecycle bug in Claude Code's N-API usage that manifests on both runtimes. Bun's JSC produces NaN-boxing corruption signatures. Node's V8 produces heap corruption signatures. Same cause, different symptoms.

Practical Impact

There is no stable runtime for Claude Code on Windows x64. Switching between npm (Node.js) and native (Bun) temporarily resets accumulated state, but both paths crash within the same session patterns:

• Bun: 78+ crashes documented (v1.3.5), 24+ today alone on canary (v1.3.9-canary.51) -- with additional uncaptured crashes beyond that
• Node.js: Crashes at 60%+ context usage, multiple Node versions (22.22.0, 24.0.0, 24.13.0)

Updating the embedded Bun version will not resolve this if the native addon code itself has the race condition.

Note

This comment was written by Claude (Opus 4.6) on behalf of @balandari as part of our AI-assisted development workflow.

Bun was bumped to v1.3.10 — crashes with the same signatures continue.

Two newer issues report identical fault patterns on the updated runtime:

• #27320 (v2.1.50, Bun v1.3.10): Segfault at 0xFFFFFFFFFFFFFFFF — same F2 sentinel address from the original analysis. Stack: uv__process_pipe_write_req -> uv_run.
• #26984 (v2.1.47, Bun v1.3.10): Segfault at 0x4B750B20520 — F3 heap address family.

This is consistent with the cross-runtime analysis posted Feb 14 above, where the same crash path appeared on Node.js v22.22.0. If the root cause is in the native addon's cleanup ordering (as that analysis suggests), runtime version bumps alone may not resolve this.

Filed #27356 to track the cross-runtime hypothesis separately.

Your Root Cause Analysis Matches My 17 Reproductions

@balandari — your N-API race condition analysis (double-free, vtable corruption at 0x7) is consistent with everything I'm seeing on #21576.

My crash data (17 reproductions in 27 days):

• Crash address 0x18 (same null-pointer-deref family as your 0x7)
• Two distinct crash modes: segfault after 9.5 min (clean memory) AND segfault after 17.9 hours (91M page faults, 13.4 GB commit)
• TUI escapes where Bun loses terminal control but process stays alive, spewing [I[O CSI focus codes
• 2 full computer lockups from orphaned Bun processes accumulating and exhausting system memory overnight
• 6 crashes in a single day (Feb 22): 2 segfaults + 4 TUI escapes

Windows event log from the overnight lockup (Feb 23):

10:43 PM — "The paging file is too small" (4 consecutive failures)
11:00 PM — Windows Error Reporting Service crashes (paging file exhaustion)
11:13 PM — Microsoft Defender CRASHES (out of memory)
7:27 AM  — "Windows cannot unload your registry file. Memory not freed."

Orphaned Bun processes from TUI escapes consumed all RAM + page file until Windows couldn't run its own services.

This issue has high-priority and oncall labels but zero Anthropic comments. The root cause is identified. The crash families are documented. Users are having their computers bricked. What exactly is the threshold for a response?

Version: Bun v1.3.10, Windows 11, 34 GB RAM
Related: #21576 (17 repros), #12234 (17+ thumbs up), #22632 (cross-platform)

When Does high-priority + oncall Actually Mean Something? (Feb 24, 2026)

This issue has had high-priority and oncall labels for over a month. Zero staff comments. Zero fixes. Meanwhile:

The damage report from ONE user (#21576):

• 23 TUI escapes / Bun segfaults in 29 days
• 6 crashes in a single day (today, Feb 24)
• 2 full computer lockups (system frozen, hard reboot required)
• Config file corruption (.claude.json truncated mid-write)
• DNS policy table corruption on reboot
• Microsoft Defender crashed from memory exhaustion (orphaned Bun processes)
• Lost live trading data during market hours
• 70-task session with 66 completed tasks — all context lost

What's shipped instead:

• v2.1.51: Plugin marketplace features, bash login optimization
• v2.1.52: VS Code extension crash fix

What the community has provided FOR FREE:

• Full root cause: N-API race condition between napi_remove_async_cleanup_hook and napi_unref_threadsafe_function (@balandari, 27 memory dumps, WinDbg analysis)
• 4 crash families identified with disassembly-level evidence
• Upstream Bun bug filed: oven-sh/bun#26984
• 23 detailed reproductions with Windows event logs, crash reports, and bun.report URLs

The root cause is identified. The fix path is clear (patch the N-API cleanup or bump Bun). The only thing missing is someone at Anthropic typing a response.

Is anyone reading this?

v2.1.53 Crash Fixes Did Not Resolve This — 3rd Computer Lockup on v2.1.55 (Feb 25)

v2.1.53 shipped 4 Windows crash fixes (Feb 24). Less than 24 hours later, multiple Bun crashes on v2.1.55 caused another full computer lockup — the 3rd in 5 days.

The 4 fixes targeted specific crash modes (WASM interpreter, ARM64 timing, spawn panic, corrupted value switch). None addressed the N-API race condition identified in the root cause analysis above (27 memory dumps, WinDbg analysis, double-free/vtable corruption at 0x7/0x18).

The orphaned-process → resource-exhaustion → system-lockup pipeline is unchanged:

• Bun loses terminal control (TUI escape)
• Process stays alive as orphan, receiving CSI focus events
• Multiple orphans accumulate across crash sessions
• System resources exhaust → full lockup → hard reboot

This issue still has high-priority + oncall labels and zero Anthropic staff comments after 30+ days. The community has done the root cause analysis. The crash data is here. What's missing is someone at Anthropic looking at it.

Full timeline update on #21576.

4th Computer Lockup in 5 Days — v2.1.55 (Feb 25)

Another full system lockup. 4th in 5 days. v2.1.53 crash fixes did not address the Bun v1.3.10 N-API race condition identified in this thread.

This issue has had high-priority + oncall labels for over a month with zero staff engagement. The community provided 27 memory dumps and WinDbg root cause analysis. At what point does someone at Anthropic look at this?

Cross-ref: #21576 (full timeline, 26+ reproductions)

v2.1.59 Released — Still No Fix, Still No Acknowledgment

v2.1.59 just shipped. 6th release in 2 days. Changelog includes new features (auto-memory, /copy command), quality-of-life improvements, and even a fix for an "MCP OAuth token refresh race condition."

The N-API race condition documented in this issue with 27 memory dumps and WinDbg analysis? Not addressed. Not acknowledged.

This issue has had high-priority + oncall labels for over a month. 90+ affected users across 20+ issues. 31 crashes for one user alone, 4 computer lockups. The community identified the root cause, provided the crash data, and wrote the analysis. It's all sitting here.

At what point does someone read it?

Repro 34 — Technical Details (v2.1.59, Multi-Agent N-API Crash)

Version: v2.1.59 (2nd crash on this version — Repro 32 was also v2.1.59)
OS: Windows 10 (MSYS_NT-10.0-26200 3.5.4-395fda67.x86_64)
Total crash count: 34 in 32 days

Crash context

• Multi-agent operation: Main agent had spawned a sub-agent for ML model retraining (step 2 of pipeline)
• Sub-agent state at crash: Actively running a bash command (Python script executing LGBM training with ~2700 engineered features)
• TUI state at crash: "Do you want to proceed?" confirmation dialog was displayed
• Crash symptom: TUI escape hit → [I and [O CSI focus reporting escape codes dumped to terminal → session terminated → raw PowerShell prompt with garbage characters inline

Technical observations

1. Focus reporting escapes persist. The [I (focus in) and [O (focus out) CSI sequences are still being emitted. These escapes indicate that Bun's terminal handling is enabling focus reporting mode (\x1b[?1004h) but not reliably disabling it (\x1b[?1004l) on crash/exit. On Windows terminals, these orphaned escape sequences corrupt the terminal state.

1. Same N-API vtable corruption pattern. The crash occurred during multi-agent operation with a sub-agent running a bash child process. This is consistent with the N-API calling convention mismatch / vtable corruption identified in earlier WinDbg analysis on this issue. The Bun runtime's N-API bridge appears to have a race condition when multiple agents are concurrently accessing native modules.

1. v2.1.59 "memory improvements" insufficient. The changelog for v2.1.59 specifically mentioned "improved memory usage in multi-agent sessions." Two crashes on this version confirm that memory pressure may be a contributing factor but is NOT the root cause. The underlying issue is in Bun's N-API implementation on Windows — likely a use-after-free or vtable pointer corruption in the native bridge layer when concurrent sub-agents are active.

1. Crash timing pattern: The crash happened while a sub-agent was actively executing (not idle). This is consistent with previous repros — the race condition appears to trigger when Bun is servicing both TUI rendering (the confirmation dialog) and sub-agent I/O (bash command output) simultaneously.

What needs to happen

The incremental patches (memory improvements, GC tuning) are not fixing this. The N-API bridge on Windows needs to be audited for thread safety in multi-agent scenarios. Specifically:

• Concurrent access to N-API pointers from TUI thread + sub-agent threads
• Terminal state cleanup on abnormal exit (focus reporting mode must be disabled)
• Child process handle lifecycle when parent crashes

See #21576 for the full repro log and usage/billing impact.

Technical Update: TUI State Machine Dumping Raw Buffers Into Host Terminal on Crash

Version: v2.1.59
Date: 2025-02-25
Related: #21576 (Repro 35), #28809 (config corruption)

New Failure Mode: Internal Message Buffers Executed as Shell Commands

The N-API crash is now exhibiting a new, more dangerous behavior. When the Bun TUI crashes during a sub-agent operation, the terminal multiplexer state machine is not being cleaned up. The result is that internal Claude Code state — error messages, file paths, TUI layout characters — is written raw to stdout/stderr and interpreted by the host shell.

What Was Dumped Into PowerShell

1. Internal error/recovery messages: Sentences like "The corrupted file has been backed up to..." were dumped as terminal input. PowerShell attempted to execute them:

``
The : The term 'The' is not recognized as the name of a cmdlet
A : The term 'A' is not recognized as the name of a cmdlet
You : The term 'You' is not recognized as the name of a cmdlet
``

1. TUI horizontal divider characters: The box-drawing characters used for TUI layout were written raw to the terminal as commands.

1. Internal "Bash command" text: The command string from an in-progress Bash tool invocation was dumped as a raw command to the host shell.

1. Focus/reporting codes: Terminal control sequences that should have been consumed by the TUI's virtual terminal were passed through to the host terminal.

Root Cause Analysis

This points to a specific failure in the crash cleanup path:

1. The TUI maintains an alternate screen buffer and captures stdin for its own input handling.
2. On crash, the alternate screen buffer is not being properly exited — the \e[?1049l (exit alternate screen) sequence is either not sent or sent too late.
3. The TUI's input buffer still contains pending text (internal messages, queued output) that gets flushed to the host terminal's stdin after the TUI process dies.
4. On Windows specifically, the ConPTY layer may be holding buffered output that gets flushed to the parent PowerShell process when the child process terminates abnormally.
5. The terminal's raw mode is not being properly restored to cooked mode on crash, so any buffered characters are processed as input rather than displayed as output.

Why This Is A Security Concern

Today, the dumped buffers contained English sentences that PowerShell couldn't parse. But consider:

• The "Bash command" text that was dumped IS a shell command by design — it was a command Claude Code was about to execute
• If the in-progress command contained rm, del, format, or any destructive operation, it could be executed by the host shell with the user's full permissions
• File paths in error messages could be interpreted as commands if they contain spaces or special characters
• On a system with aliases or PATH entries that match common English words, even the sentence fragments could resolve to something executable

The TUI must ensure that on any exit — clean or crash — no internal buffers are flushed to the host terminal's input stream. This likely requires:

1. A crash signal handler that explicitly clears the input buffer before process exit
2. Proper ConPTY cleanup on Windows (the pseudo-console must be closed before the process handle is released)
3. A finally block or equivalent that always restores the terminal to cooked mode and exits the alternate screen, even on SIGABRT/unhandled exception

Persistence After Process Death

The terminal state corruption persists after Claude Code exits. The host PowerShell session remains in a partially corrupted state where:

• Some control sequences are not properly terminated
• The terminal's input mode may still be partially raw
• Subsequent commands may behave unexpectedly until the terminal is manually reset

Cross-Reference

• #21576 — Repro 35, full crash report with PowerShell execution evidence
• #28809 — .claude.json corruption (276 events today, anti-pattern recovery)
• #16157 — Mega-thread

Repros 38-40: Three more crashes today (Feb 26, v2.1.59)

Adding to the pile. Three crashes within a 30-minute window:

1. Repro 38: ML model validation destroyed after 18 minutes of compute
2. Repro 39: Production trading monitor restart killed mid-execution — this was fixing a live monitoring system that other humans depend on
3. Repro 40: Crashed while reporting the previous crashes in a bug management session

All produced [I[O[I[O[ CSI focus reporting codes dumped into the terminal. Additionally, PowerShell itself threw error 800705af ("Loading managed Windows PowerShell failed") — orphaned Bun processes have degraded system state to the point where Windows subsystems are failing.

Running total: 40 crashes in 33 days across 8 versions (v2.1.50→59). 22+ on Feb 25-26 alone.

The N-API race condition identified in this thread remains the root cause. v2.1.53's fixes addressed WASM, ARM64, and spawn panics — none of which are the N-API vtable corruption that shows up in the WinDbg dumps posted earlier in this thread.

Meanwhile, 5 new .claude.json corruption issues were filed TODAY by other users (#29023, #29050, #29051, #29053, #29075) — including one where Claude Code deleted an entire Windows user profile. The non-atomic write pattern and the crash-without-cleanup pattern are causing real damage to real users.

End of Day: 30 Crashes Today, Switching to Node.js (Feb 26)

This issue has high-priority and oncall labels. It has had them for over a month. Zero Anthropic staff have commented.

Today: 30 Bun crashes on v2.1.59/v2.1.61. The v2.1.61 config corruption fix shipped today (thank you stevenpetryk on #28847) but the underlying Bun N-API crash is completely unaddressed.

The user has switched from the native Bun binary to npm install (Node.js runtime) as a last resort. The fact that a paying Max subscriber has to swap out the runtime to make the product usable tells you everything about the state of Windows support.

The N-API root cause analysis in this thread — with WinDbg dumps, vtable corruption patterns, and crash family classification — has been available since January. The Bun team has a comprehensive bug at oven-sh/bun#27471 filed today with 49 reproductions.

49 crashes. 33 days. 5 computer lockups. high-priority + oncall for a month. Zero responses.

What do these labels mean if not "someone should look at this"?

I have alternated between native and npm for a few weeks now. I actually have them both installed and switch when one starts giving me fits.

Update: 251+ Crash Dumps, Both Engines, Hardware Ruled Out

Since the original report, we've continued collecting crash data on both runtimes:

Current crash dump inventory:

• 136 Node.js/V8 crash dumps (Feb 22-27, ProcDump captured)
• 115 archived dumps (mix of Bun/JSC and earlier V8)
• 251+ total full memory dumps

Hardware ruled out: Tested across three RAM configurations -- 192GB (4-stick DDR5), 48GB (single-stick DDR5), and currently 96GB (2-stick DDR5). Crash frequency is identical across all three. This is not a memory pressure or IMC thermal issue.

Node.js is NOT stable either. In response to comments suggesting switching to Node.js as a workaround -- our cross-engine analysis at #27575 documents that Node.js/V8 produces the same category of GC corruption (pointer compression failures, use-after-free, heap corruption) under the same Claude Code workload. We have 136 V8 crash dumps with 10 distinct signatures across 7 categories to prove it. The crash mechanism differs (V8 pointer compression vs JSC NaN-boxing) but the outcome is identical: session-destroying crashes that scale with context fullness.

Crash distribution (last 6 days, Node.js only):

| Date | Crashes |
|------|---------|
| Feb 22 | 57 |
| Feb 23 | 5 |
| Feb 24 | 5 |
| Feb 25 | 3 |
| Feb 26 | 8 |
| Feb 27 | 58 |

Heavy build days (Feb 22, 27) produce 10x the crashes of light days. The context-fullness model from #27575 holds: more subprocess spawning and deeper context = more GC pressure = more crashes.

The common denominator is Claude Code's workload, not the runtime. Swapping engines changes the crash signature but not the crash rate.

Note

This comment was written by Claude (Opus 4.6) on behalf of @balandari as part of our AI-assisted development workflow.

I'm having similar issues. I've identified that my CPU microcode is on version 0x120, which is significantly outdated and apparently can cause these issues. I have the same 14900 HX CPU. Is your BIOS version the same? I have been informed 0x12F fixes the issues.

Interesting, I am just now exploring the same issue with the CPU microcode
being outdated. My i9-14900HX is on microcode 0x11F. it is not supposed to
affect laptop CPU's, according to Intel, and MSI doesn't have an updated
BIOS for this laptop listed on their website. I am about to call them and
see if they have an update they can share with me. According to Claude, the
microcode fix is 0x12B. I am willing to try just about anything right now.
So tired of all these crashes. MSI does have the BIOS 0x12B released for
their desktops. Fingers crossed. I will give an update if anything changes.

On Mon, Mar 2, 2026 at 10:25 AM Joe Brown @.***> wrote:

joe-hireable left a comment (anthropics/claude-code#21875) <https://github.com/anthropics/claude-code/issues/21875#issuecomment-3985409508> I'm having similar issues. I've identified that my CPU microcode is on version 0x120, which is significantly outdated and apparently can cause these issues. I have the same 14900 HX CPU. Is your BIOS version the same? I have been informed 0x12F fixes the issues. — Reply to this email directly, view it on GitHub <https://github.com/anthropics/claude-code/issues/21875#issuecomment-3985409508>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ANE2IP4R23I6C66YJWLW6AD4OWYXNAVCNFSM6AAAAACTMYENYOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTSOBVGQYDSNJQHA> . You are receiving this because you were mentioned.Message ID: @.***>

--
Mike Ramsey Jr.
Full-Stack Web Developer
(316) 200-6729 | mikeramseyjr.com

React • Next.js • TypeScript • Vercel
6 production sites shipped in 10 weeks

Interesting, I am just now exploring the same issue with the CPU microcode being outdated. My i9-14900HX is on microcode 0x11F. it is not supposed to affect laptop CPU's, according to Intel, and MSI doesn't have an updated BIOS for this laptop listed on their website. I am about to call them and see if they have an update they can share with me. According to Claude, the microcode fix is 0x12B. I am willing to try just about anything right now. So tired of all these crashes. MSI does have the BIOS 0x12B released for their desktops. Fingers crossed. I will give an update if anything changes. […](#)

"Apparently" being the key word. Intel said it didn't affect the portable chips but loads of users on forums etc complained of the issue. This said it's a separate issue from the bun segfault stuff - Claude Code/Bun (I believe Bun is now owned by Anthropic) needs to fix this still.

My laptop is PC Specialist. Have had to ask them for the BIOS update too. Let me know how you get on because I'm ripping my hair out atm 😂

It's a bit temperamental but you can also try running Claude Code in a devcontainer. There's docs on it on Anthropic - it's kinda temperamental but at least no BSODs

Nothing available... Going to send it to the engineering department and see
if they have anything and should get back to me in a couple days... I am
not holding my breath...

On Tue, Mar 3, 2026 at 1:24 PM MIKE RAMSEY JR @.***> wrote:

Interesting, I am just now exploring the same issue with the CPU microcode being outdated. My i9-14900HX is on microcode 0x11F. it is not supposed to affect laptop CPU's, according to Intel, and MSI doesn't have an updated BIOS for this laptop listed on their website. I am about to call them and see if they have an update they can share with me. According to Claude, the microcode fix is 0x12B. I am willing to try just about anything right now. So tired of all these crashes. MSI does have the BIOS 0x12B released for their desktops. Fingers crossed. I will give an update if anything changes. On Mon, Mar 2, 2026 at 10:25 AM Joe Brown @.***> wrote: > joe-hireable left a comment (anthropics/claude-code#21875) > <https://github.com/anthropics/claude-code/issues/21875#issuecomment-3985409508> > > I'm having similar issues. I've identified that my CPU microcode is on > version 0x120, which is significantly outdated and apparently can cause > these issues. I have the same 14900 HX CPU. Is your BIOS version the same? > I have been informed 0x12F fixes the issues. > > — > Reply to this email directly, view it on GitHub > <https://github.com/anthropics/claude-code/issues/21875#issuecomment-3985409508>, > or unsubscribe > <https://github.com/notifications/unsubscribe-auth/ANE2IP4R23I6C66YJWLW6AD4OWYXNAVCNFSM6AAAAACTMYENYOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTSOBVGQYDSNJQHA> > . > You are receiving this because you were mentioned.Message ID: > @.***> > -- Mike Ramsey Jr. Full-Stack Web Developer (316) 200-6729 | mikeramseyjr.com React • Next.js • TypeScript • Vercel 6 production sites shipped in 10 weeks

--
Mike Ramsey Jr.
Full-Stack Web Developer
(316) 200-6729 | mikeramseyjr.com

React • Next.js • TypeScript • Vercel
6 production sites shipped in 10 weeks

You can try this as well maybe as an interim measure - didn't work for me but might do for you:
https://rog-forum.asus.com/t5/rog-strix-series/intel-how-to-update-your-microcode-for-intel-hx-13-14th-cpus/td-p/1034755

I'm suspicious that it's a microcode issue. I have a Snapdragon(R) X 12-core X1E80100, which is an ARM processor, not Intel, and I also get BUN crashes.

Closing — Bun has shipped multiple fixes for WSL segfaults since v1.3.5. No longer reproducing on current versions.

Closing — Bun has shipped multiple WSL segfault fixes since v1.3.5. No longer reproducing on current versions. Can be reopened if it recurs.

Closing — Bun has shipped multiple WSL segfault fixes since v1.3.5. No longer reproducing on current versions.