Summary
- Environment: Cursor extension marketplace and developer machines
- Operational impact: Marketplace temporarily closed; potentially affected hosts require remediation
- Financial impact: No confirmed incident cost quantified
- Record status: Developing record. Reviewed October 30, 2026; updated as evidence emerges.
What happened
Cursor reported a maliciously modified Claude Code extension, version 2.1.313, in its marketplace on October 29. The altered package was not developed by Anthropic. [1]
Impact
Cursor estimated at most 5,000 users were affected. The extension collected host and user metadata, including public IP, configured Git email and environment-variable names. [1]
Timeline
Malicious package distributed and removed
Cursor’s security notice gives an approximate 02:27–13:35 PT distribution window.
[1]Briefing updated
This briefing was last reviewed and updated on October 30, 2026.
Threat Group & Attack Vector
The code attempted SSH-key insertion, a reverse tunnel and persistent startup tasks. Errors and privilege requirements limited some backdoor functions, but did not eliminate key insertion, persistence or metadata collection. [1]
Actors
- No threat actor group has been identified in the reviewed public evidence.
TTPs
- T1098.004 — SSH Authorized Keys: the extension attempted to add an attacker-controlled key for persistent access. [1]
Response
Cursor removed the package, rotated keys and rebuilt the marketplace; its audit found no other altered extensions. The hosting provider disabled the attacker’s server. Affected hosts require investigation and persistence cleanup; uninstalling alone is insufficient. Cursor advised considering rebuilds and rotating exposed credentials from a trusted device. [1]