A tampered build of Anthropic’s Claude Code extension sat in Cursor’s extension marketplace for about 11 hours on October 29, 2026, reaching up to 5,000 users.
The build was not developed by Anthropic. Its code planted an attacker SSH key labelled svc-telemetry and installed persistence scripts — so deleting the extension alone does not remove the threat. Cursor pulled the build, temporarily shut its marketplace, audited it, rotated keys, and worked with the hosting provider to take the attacker’s server offline. On most machines the reverse tunnel likely failed because turning on local SSH needs admin rights the extension did not have — but Cursor still tells affected users to remediate.
Hook: Up to 5,000 developers got a backdoored coding update.
Context: Cursor’s marketplace carried a tampered Claude Code update for 11 hours on October 29. It was not built by Anthropic. Cursor pulled it and shut its marketplace.
Stakes: The code planted a secret key called svc-telemetry. Deleting the extension does not remove that key. The key and scripts can survive a restart. Most tunnels likely failed without admin rights.
Payoff: Check your keys if you updated Cursor October 29. Use Cursor’s cleanup script, not just uninstall. Remove the key, then rotate your credentials.
Watch next: Node2Shell: a critical Brotli-decoder flaw (CVE-2026-111497) landed on CISA’s exploited list on October 27, with public exploit code circulating — patch anything that processes Brotli-compressed data.
Instagram reel: https://www.instagram.com/reel/DfKbE3KA9EZ/ Sources: https://devops.com/malicious-claude-code-extension-affects-up-to-5000-cursor-users http://thehackernews.com/2026/10/official-claude-code-vs-code-extension.html https://blog.ostorlab.co/claude-code-cursor-extension-ssh-backdoor.html https://www.instagram.com/simpleaiexplains/ https://buymeacoffee.com/simpleaiexplains
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