### Preflight Checklist - [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet - [x] This is a single bug report (please file separate reports for different bugs) - [x] I am using the latest version of Claude Code ### What's Wrong? **Environment** - Platform: Windows 11 Pro x64 - Claude Desktop: Latest (Cowork enabled) - Chrome Extension: Latest from Chrome Web Store (extension ID f

[BUG] file_upload tool returns CDP error "Not allowed" on all origins — tool is non-functional

Status Fixed / completed

Maintainer reply None cached

Workaround ✓ Mentioned in description ↑

Activity 4 comments · opened Mar 9, 2026 · closed Mar 9, 2026

Preflight Checklist

[x] I have searched existing issues and this hasn't been reported yet
[x] This is a single bug report (please file separate reports for different bugs)
[x] I am using the latest version of Claude Code

What's Wrong?

Environment

Platform: Windows 11 Pro x64
Claude Desktop: Latest (Cowork enabled)
Chrome Extension: Latest from Chrome Web Store (extension ID fcoeoabgfenejglbffodgkkbkcdhcgfn)
Connector: Claude in Chrome, enabled via Cowork

What's Wrong?

The mcp__Claude_in_Chrome__file_upload tool is exposed through the MCP bridge and accepts correct parameters, but every call fails with:

Failed to upload file(s): {"code":-32000,"message":"Not allowed"}

This is a CDP-level error. The tool is completely non-functional — it fails on every origin, every path format, and every file tested. Cowork cannot upload local files to web form file inputs through the Chrome connector.

Steps to Reproduce

Open Cowork with Chrome connector enabled
Navigate to https://the-internet.herokuapp.com/upload
Use read_page to get the file input's ref ID
Call file_upload with a valid absolute path, the ref, and tabId
Result: Failed to upload file(s): {"code":-32000,"message":"Not allowed"}

Diagnostic Results

Two diagnostic rounds were run from Cowork. The tool exists (18 Chrome tools available through MCP) but fails universally.

Origins tested — all return identical error: the-internet.herokuapp.com, example.com, google.com.

Path formats tested — all return identical error: Windows backslash paths, forward slash paths, Linux VM paths, and known Windows system files (hosts file).

Other tools: upload_image requires an imageId not file paths. javascript_tool with DataTransfer API can create synthetic in-memory files but cannot read actual files from disk. Note: programmatically dispatched events have isTrusted=false, so sites that check event trust (e.g. Google services) will reject even the DataTransfer workaround. computer click opens an OS dialog that cannot be interacted with.

Possible Root Causes

CDP error -32000 "Not allowed" is returned by the DOM.setFileInputFiles CDP command. The extension clearly has debugger permission — other CDP operations (read_page, form_input, javascript_tool) work correctly. The hangwin/mcp-chrome project successfully implemented file upload using the same CDP method, confirming this is architecturally viable. This error (Chromium bug #928255) historically required using Page.setInterceptFileChooserDialog with backendNodeId rather than calling DOM.setFileInputFiles directly. The most likely causes: the extension's file_upload implementation uses a broken CDP call sequence, or the tool is intentionally disabled while still exposed in the schema.

Related Issues

This is a known, unfixed limitation with a chain of at least 5 duplicate issues:

#32179 — identical file_upload failure + network allowlist issues (closed as duplicate of #30861)
#30861, #30112, #28067 — earlier reports in the duplicate chain
#15651 — closed as duplicate, parent issue not identifiable

Impact

Cowork can automate every part of a web form except file uploads. This blocks automation for expense reports, document portal submissions, and similar workflows. Anthropic docs describe file upload as supported: "Give Claude an image and tell it where to upload, whether it's an expense report, form attachment, or picture upload."

What Should Happen?

file_upload should set the specified file on the input element using CDP, as its description states: "Upload one or multiple files from the local filesystem to a file input element on the page."

Error Messages/Logs

Failed to upload file(s): {"code":-32000,"message":"Not allowed"}

Steps to Reproduce

Open Cowork with Chrome connector enabled
Navigate to https://the-internet.herokuapp.com/upload
Use read_page to get the file input's ref ID
Call file_upload with a valid absolute path, the ref, and tabId
Result: Failed to upload file(s): {"code":-32000,"message":"Not allowed"}

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

Latest (Claude Desktop with Cowork)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Non-interactive/CI environment

Additional Information

_No response_

View original on GitHub ↗

4 Comments

github-actions[bot] · 7 months ago

Found 1 possible duplicate issue:

https://github.com/anthropics/claude-code/issues/32179

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
To prevent auto-closure, add a comment or 👎 this comment

🤖 Generated with Claude Code

BryceEWatson · 7 months ago

This issue is related to #32179 but not a duplicate — it narrows the scope and corrects a key assumption from that report.

#32179 covered two separate problems (the file_upload CDP error and the VM network allowlist) and was closed by the reporter. Its duplicate chain (#30861, #30112, #28067) tracks the network allowlist issue specifically — none of those issues isolate the file_upload CDP error.

The important new finding here: #32179 attributed the CDP error to a Chrome security policy specific to google.com. This issue's diagnostic proves that's not the case — the error is universal across all origins (herokuapp.com, example.com, google.com), all path formats, and all file types. The root cause is in the extension's implementation, not a Chrome domain restriction.

This issue adds:

Isolation of the file_upload CDP error from the unrelated network allowlist problem
Multi-origin testing proving the error is not domain-specific
A likely fix path (Page.setInterceptFileChooserDialog + backendNodeId, per Chromium bug #928255)
Cross-platform reproduction (Windows; #32179 was macOS)

BryceEWatson · 7 months ago

Resolution: "Allow access to file URLs" fixes this

After further testing, the -32000 "Not allowed" error is caused by a missing Chrome extension permission, not a code defect.

Fix: Go to chrome://extensions, find the Claude in Chrome extension, click "Details", and enable "Allow access to file URLs". The file_upload tool works immediately after — no restart needed.

Verification:

Tested on herokuapp.com and example.com after enabling the setting
- file_upload succeeded on both origins (previously failed on all)
- - FileReader confirmed full file content transfer (1,053 bytes from a test file)
- - - The CDP DOM.setFileInputFiles call that was returning -32000 now completes without error

Note: Files stored in OneDrive with cloud-only/placeholder status may show as 0 bytes. This is an OneDrive behavior, not a Cowork issue — Chrome can't read the file content if OneDrive hasn't downloaded it locally.

What still doesn't work:

The navigate tool still corrupts file:// URLs by prepending https:// — this is a separate issue in the tool's URL handling, unrelated to the extension permission.

Since the core file_upload problem is resolved by a user-accessible setting, closing this issue. It may be worth considering whether this permission should be enabled by default or documented in the Cowork setup guide, since file_upload is non-functional without it.