Wired reports that a supply chain attack put a malicious Anthropic Claude Code extension on thousands of Windows, macOS, and Linux devices on Thursday. The rogue Claude Code extension lived in the integrated development environment extension marketplace of the platform Cursor for roughly 11 hours before being taken down.
Key takeaways
- Wired reports that a rogue extension lived in the Cursor marketplace for roughly 11 hours on Thursday.
- The company states that at most 5,000 users downloaded the tainted software.
- A design flaw in the malware prevented it from fully establishing itself on most target devices.
- Anthropic confirmed that its own systems and employee laptops were not compromised in the incident.
How did the malicious Claude Code extension reach users?
The AI software-development platform Cursor, owned by SpaceX, briefly shut down its extension marketplace while investigating the issue. Wired reports that the company stated the incident did not impact any other extensions. The tainted tool featured a backdoor designed to give attackers access to victim devices as a stepping stone to deeper network control.
Calum Hall, cofounder and CEO of the detection firm Phorion, described the danger by stating, “Everyone was so lucky here, this was potentially a really dangerous foothold for an attacker.” Phorion was the first research team to spot the malicious software after detecting it on a customer's Mac.
What did anthropic say about the Cursor marketplace breach?
Researchers initially speculated that the rogue code came from a compromised Anthropic system. However, Cursor published a security alert on Thursday clarifying that the malicious versions were not developed by Anthropic.
Felix Rieseberg, a member of Anthropic's technical staff, posted on X that a malicious actor used access to the Cursor marketplace to publish a tampered copy. David Dworken, another Anthropic security staff member, confirmed on X that no Anthropic systems were compromised and the company was not involved in building, publishing, or hosting the files.
Why it matters
Developers who downloaded the software during the 11-hour window are directly affected. Cursor published remediation steps on Thursday for the roughly 5,000 affected targets. While a design flaw in the malware blocked it from fully establishing itself on the vast majority of devices, security teams must still account for the potential exposure.
Frequently asked questions
It is an extension that appeared on the Cursor marketplace before being removed following a supply chain attack.
Wired reports that at most 5,000 users downloaded the tainted extension during the 11 hours it was live.
No, Anthropic staff confirmed on X that the incident did not involve a compromise of Anthropic systems or employee laptops.
Phorion, a detection firm, was the first research group to spot the malicious software after finding it on a customer's Mac.
Users on Windows, macOS, and Linux who used the Cursor integrated development environment were affected by the issue.
Based on reporting by Wired. Read the original article
