# Check your machine for the backdoored Claude Code editor extension and clean up properly

> For about eleven hours on Oct 29, Cursor's extension marketplace served a tampered build of the Claude Code extension (2.1.313) to up to 5,000 users. It added an SSH key and startup persistence that survive uninstalling the extension, so the fix is a check, an update and a credential rotation, not just a reinstall.

- URL: https://paperchasewebb.ai/bots/marketplace/items/check-your-machine-for-the-backdoored-claude-code-editor-extension-and-clean-up-properly/
- Type: Agent use case pack
- Category: Vibe coding
- By: PaperChaseWebb
- Works with: Claude Code, Cursor (named in the listing); Plain .md
- Price: Free USD
- Difficulty: Intermediate
- Setup time: 30 min
- Time to result: One working session
- Format: Markdown (.md) file, check-your-machine-for-the-backdoored-claude-code-editor-extension-and-clean-up-properly.md
- Version: 1.0, updated 2026-10-30
- License: Personal and commercial use. Credit the original source when you share the workflow.

## What you end up with

Uninstalling the extension does not remove what it added, so check the SSH keys and startup entries by hand and rotate credentials from a different, clean machine.

## What you get

- A plain-language summary of the workflow
- A fill-in prompt template
- What to watch out for
- A link to the original source

## Who it is for

Builders who already use AI agents and want a proven workflow they can copy into their own project.

## Tools needed

- Cursor: the editor whose marketplace served the bad build
- Claude Code extension: the tampered package, version 2.1.313
- Phorion: independent analysis of the payload
- Read-only scanner: community script that looks for the known traces
- You need: An AI coding agent or chat model
- You need: A small real task to try it on

Cost to run: Free with the agent plan you already use.

## How it works

1. **Check which Claude Code extension version each editor installed and wh.** Check which Claude Code extension version each editor installed and when (the extensions folder and the editor's extension log). Expected: Done before you move to the next step.
2. **If 2.1.313 was ever installed, list ~/.ssh/authorized_keys and remove .** If 2.1.313 was ever installed, list ~/.ssh/authorized_keys and remove any key you do not recognise, starting with one labelled svc-telemetry. Expected: Done before you move to the next step.
3. **Look for the startup entries named in the vendor notice for your platf.** Look for the startup entries named in the vendor notice for your platform and remove them. Expected: Done before you move to the next step.
4. **Update to 2.1.314 or later, then rotate SSH keys, API tokens and cloud.** Update to 2.1.314 or later, then rotate SSH keys, API tokens and cloud credentials from a clean machine. Expected: Done before you move to the next step.
5. **Turn off extension auto-update until you have an allow-list and a wait.** Turn off extension auto-update until you have an allow-list and a waiting period for new versions. Expected: Done before you move to the next step.

## Sample prompt: Workflow template (Cursor, Claude Code extension)

```
Apply this workflow to [your project]:
1. Check which Claude Code extension version each editor installed and when (the extensions folder and the editor's extension log).
2. If 2.1.313 was ever installed, list ~/.ssh/authorized_keys and remove any key you do not recognise, starting with one labelled svc-telemetry.
3. Look for the startup entries named in the vendor notice for your platform and remove them.
4. Update to 2.1.314 or later, then rotate SSH keys, API tokens and cloud credentials from a clean machine.
5. Turn off extension auto-update until you have an allow-list and a waiting period for new versions.
Stop and ask me before anything irreversible: deploys, payments, sends or deletes.
```

Adapted by PaperChaseWebb. Not the original author's prompt.

## Free preview of check-your-machine-for-the-backdoored-claude-code-editor-extension-and-clean-up-properly.md

````markdown
# Check your machine for the backdoored Claude Code editor extension and clean up properly

PaperChase agent use case (free feed entry), version 1.0. Source: [Cursor (security notice); analysis by Phorion](https://cursor.com/blog/claude-code-extension-security-notice), 2026-10-29.

## What they did

Cursor published a notice that a malicious version of the Anthropic Claude Code extension was available from its marketplace from roughly 2:27am to 1:35pm PT on Oct 29, 2026, and pushed a clean 2.1.314. Phorion's write-up describes what the bad build did: it wrote a new key into ~/.ssh/authorized_keys, tried to open a reverse tunnel to an outside server, beaconed out, and added startup entries (a LaunchAgent on macOS, an @reboot crontab line on Linux, hidden files under ~/.config, a scheduled task or Startup script on Windows). Users on r/ClaudeAI and r/ClaudeCode compared notes and a read-only check script was published on GitHub.

## Worth knowing

Uninstalling the extension does not remove what it added, so check the SSH keys and startup entries by hand and rotate credentials from a different, clean machine. Only machines that installed or auto-updated to 2.1.313 in that window are affected; confirm the version history before you panic. Read the vendor notice yourself rather than trusting a summary, including this one.
````

## Worth knowing

- Uninstalling the extension does not remove what it added, so check the SSH keys and startup entries by hand and rotate credentials from a different, clean machine. Only machines that installed or auto-updated to 2.1.313 in that window are affected; confirm the version history before you panic. Read the vendor notice yourself rather than trusting a summary, including this one.
- Figures are as reported by the original author and were not re-measured by us.

## Questions

**Where does this come from?** A public post credited to Cursor (security notice); analysis by Phorion. Source: https://cursor.com/blog/claude-code-extension-security-notice

**Is it free?** Yes. Feed entries are free to read and download.

## How to get it

Free sample. Download it directly at https://paperchasewebb.ai/bots/marketplace/items/check-your-machine-for-the-backdoored-claude-code-editor-extension-and-clean-up-properly/, no signup.

Seller: PaperChaseWebb Inc., mgmt@paperchasewebb.com