Key points
- A compromised Claude Code extension was live on Cursor's marketplace for approximately 11 hours.
- The malware attempted to collect system data and establish remote access on affected machines.
- Cursor removed the extension and took the entire marketplace offline to neutralize the threat.
Cursor reported that a tampered version of the Claude Code extension was available in its VS Code extension marketplace on Thursday, affecting up to 5,000 users.reported The company stated that Anthropic had no involvement in developing or distributing this specific compromised package.
Evidence: reported
Malicious Claude Code extension in Cursor's marketplace attempted remote access and data theftaifleet-decoder
What was released or claimed
The malicious extension attempted to harvest sensitive user data, including hostnames, usernames, operating system details, and public IP addresses. According to Cursor, the software also tried to set up remote access for attackers, though the company noted this likely failed on most machines because it requires administrative privileges.reported
Evidence: reported
Malicious Claude Code extension in Cursor's marketplace attempted remote access and data theftaifleet-decoder
Who it affects
Up to 5,000 users who installed the extension during the 11-hour window of availability were potentially affected.reported Cursor confirmed that no other extensions in the marketplace were impacted by this specific incident.
Evidence: reported
Malicious Claude Code extension in Cursor's marketplace attempted remote access and data theftaifleet-decoder
What is still unknown
It remains unclear how many of the 5,000 affected users actually had the remote access component succeed, given the requirement for admin privileges.reported The source material does not specify the exact identity of the attacker or the method used to compromise the extension before it went live.
Evidence: reported
Malicious Claude Code extension in Cursor's marketplace attempted remote access and data theftaifleet-decoder
What changes, what does not
Cursor pulled the specific extension and took the entire marketplace offline to ensure safety. After working with providers to neutralize the malware and confirming there was no further risk, the marketplace was reinstated. No other extensions were affected.
Methods and limits
This report relies on statements from Cursor regarding the scope and nature of the compromise. The company identified the specific data types targeted and the technical limitation (admin privileges) that likely prevented full remote access. The timeline of 11 hours and the user count of 5,000 are estimates provided by Cursor.reported No independent verification of the malware's code or the exact number of successful data exfiltrations is provided in the source material.
Evidence: reported
Malicious Claude Code extension in Cursor's marketplace attempted remote access and data theftaifleet-decoder
Why it matters
- Platform architects must verify that third-party extensions, even those with legitimate names, are signed and verified by their original developers.
- The incident highlights the risk of supply-chain attacks within IDE marketplaces, where a single compromised package can reach thousands of developers quickly.
- The requirement for admin privileges to establish remote access served as a partial mitigation, underscoring the importance of least-privilege configurations in development environments.
- Full marketplace takedowns are a valid but disruptive response to malware, indicating that platform operators may prioritize safety over availability when threats are detected.
Topics: Cursor, Anthropic, security, extensions, malware
Updated
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Your choice stays on this device. No public tally.Questions readers ask
Did Anthropic create the malicious extension?
No, Cursor stated that Anthropic had no involvement in developing the tampered extension found in its marketplace.
How long was the malicious extension available?
The tampered extension was live on the Cursor marketplace for about 11 hours before being discovered and removed.
Was any other extension affected by this incident?
No, Cursor confirmed that no other extensions in the marketplace were affected by this specific compromise.
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Reading receipt
- A compromised Claude Code extension was live on Cursor's marketplace for approximately 11 hours.
- The malware attempted to collect system data and establish remote access on affected machines.
- Cursor removed the extension and took the entire marketplace offline to neutralize the threat.