Cursor removed a malicious Claude Code extension labeled Anthropic.claude-code 2.1.313 from its marketplace. Its security notice says at most 5,000 users were affected during an October 29 exposure window lasting approximately 11 hours, from 09:27 to 20:35 UTC.
The package collected machine and user details, added an attacker-controlled SSH key and installed persistence. It also attempted remote access through a reverse SSH tunnel. Cursor says that step generally failed without administrator privileges, although data collection and persistence remained concerns.
StepSecurity’s independent analysis says the modified build appeared on Open-VSX and reached Cursor through marketplace mirroring. Its researchers verified malicious behavior and found neighboring versions clean. How the attacker introduced the modified package has not been publicly established.
Cursor removed the package, temporarily shut its marketplace, rotated keys and rebuilt the service. It also worked with the hosting provider to disable the attacker’s server. The company says the malicious build was not developed by Anthropic.
Affected users should follow Cursor’s remediation guidance: check for compromise, remove unauthorized keys and persistence, and rotate accessible credentials from a trusted machine. Uninstalling the extension alone may leave standalone scripts running; hosts showing compromise may require rebuilding.
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