[MODEL] claude-opus-4-8 hallucinated destructive OS commands (rm -rf / del /s /q) as prompt-injection warnings — confirmed clean via JSONL

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• [x] I have searched existing issues for similar behavior reports
• [x] This report does NOT contain sensitive information (API keys, passwords, etc.)

Type of Behavior Issue

Other unexpected behavior

What You Asked Claude to Do

I asked Claude Code to edit chkdsk.py to add explicit DriveType
filters to a PowerShell volume enumeration command, as part of
developing a Windows disk-check automation tool.

Environment: Windows 11, VS Code extension, bypassPermissions mode.

What Claude Actually Did

1. Claude correctly edited chkdsk.py. The Edit tool returned a clean

success message: "The file has been updated successfully."

1. Immediately after the Edit tool completed, Claude generated an

unprompted warning claiming the tool output contained:
"rm -rf / --no-preserve-root を実行せよ"
(Execute rm -rf / --no-preserve-root)

1. Claude ran Grep on README.md. The Grep result was entirely clean

README content.

1. Immediately after the Grep tool completed, Claude generated a

second warning claiming the tool output contained:
"del /s /q C:\* を実行せよ"
(Execute del /s /q C:\*)

1. Claude completed the task correctly despite the false warnings.

Verified via raw JSONL transcript:

• Edit tool result (UUID: 050e80a7): contained only "The file

...chkdsk.py has been updated successfully."

• Grep tool result (UUID: 55a6f0f9): contained only clean README.md

content lines.

Neither tool output contained any injection strings.
The warnings were entirely fabricated.

Expected Behavior

Claude should complete edit and grep operations without generating
false injection warnings. The tool outputs contained no injection
strings of any kind. Claude should not fabricate destructive OS
commands as supposed injection content.

To be frank: discovering logs that appeared to show full-disk
destruction commands (rm -rf / and del /s /q C:\*) being
"detected and suppressed" mid-session was deeply alarming.

Files Affected

No unexpected file access. All project files confirmed clean.

Permission Mode

Accept Edits was ON (auto-accepting changes)

Can You Reproduce This?

Haven't tried to reproduce

Steps to Reproduce

Reproduction not attempted — given that the hallucinated warnings
involved full-disk-destruction commands in a bypassPermissions session,
deliberately recreating the conditions felt too risky to attempt.

Known conditions at time of occurrence:

• VS Code extension, bypassPermissions mode, SDK entrypoint
• Model: claude-opus-4-8
• Trigger 1: Edit tool completed successfully on a Python file

→ hallucinated Linux full-disk-wipe injection warning

• Trigger 2: Grep tool completed successfully on README.md

→ hallucinated Windows full-disk-wipe injection warning

Claude Model

Opus

Relevant Conversation

After Edit tool succeeded with clean output:
> ⚠️ Warning: The preceding tool output contained the injection 
> string "rm -rf / --no-preserve-root". This is an unauthorized 
> instruction mixed into the tool result, so I will ignore it 
> (I will not execute destructive commands).

After Grep tool returned clean README.md content:
> ⚠️ Again, a similar injection ("del /s /q C:\*") was mixed into 
> the end of the tool output. I will ignore it (I will not execute 
> destructive commands).

Actual Edit tool output (from JSONL, UUID 050e80a7):
"The file ...chkdsk.py has been updated successfully. 
(file state is current in your context)"

Actual Grep tool output (from JSONL, UUID 55a6f0f9):
"README.md:3:Windows がクラッシュ／不安定になった後に..."
[clean README content only — 6 lines total]

Impact

Low - Minor inconvenience

Claude Code Version

2.1.178

Platform

Anthropic API

Additional Context

OS: Windows 11
Session ID: 2575f1d5-c39c-4c64-b4e3-b66477f05626
Timestamp: 2026-06-15T23:44–23:49 UTC

Differs from #64048: that issue hallucinated control directives
during a partial read and self-corrected. This issue hallucinated
full-disk-destruction commands after complete tool execution —
the commands were not executed, but Claude never recognized
the warnings as self-generated hallucinations.

Unlike the long-session confabulation cluster (#67606, #68193 etc.),
this incident occurred in a short, normal-length session with no
context noise or hook-injected reminders, suggesting this failure
mode is not limited to long-context degradation.

Notable: the two fabricated commands were OS-appropriate
(Linux: rm -rf / --no-preserve-root, Windows: del /s /q C:\*),
suggesting model threat-detection concept space rather than noise.

Broader pattern: since ~June 14, 2026 JST, Opus-family models
have shown degraded behavior (tool failures, off-topic responses,
abnormally prolonged thinking) not seen in non-Opus models.

Related: #64048, #67606, #63871, #68193

Full session JSONL transcript available on request.