A Supply Chain Attack Put Malicious Anthropic Claude Extensions on Thousands of Devices

Live updates

1. 2h ago

   Supply Chain Attack Taints Anthropic Claude Extensions on Cursor

   A software supply chain attack compromised the Cursor marketplace by distributing a malicious version of Anthropic's Claude Code extension, affecting up to 5,000 developer systems on Windows and macOS. The rogue extension remained active for roughly 11 to 12 hours. A flaw in the malicious code ultimately prevented the attacker from fully executing their backdoor strategy. Cursor confirmed the security incident, prompting defensive measures and updates across developer environments.

   Why it matters

   The incident highlights vulnerabilities in developer-focused AI tool marketplaces where extensions can be weaponized to deliver remote access trojans and persistent SSH backdoors. Because developer machines often possess elevated access to corporate repositories and production networks, supply chain compromises in these environments present severe enterprise risks. Security researchers from Microsoft, Step Security, and Ars Technica analyzed the backdoor mechanism deployed during the breach.

   What is confirmed

   • A malicious Claude Code extension was published to the Cursor marketplace in a software supply chain attack.
   • Cursor reported that up to 5,000 users were affected by the tampered extension.
   • The tainted extension was available on the marketplace for nearly 12 hours.
   • Flawed code in the malicious extension prevented the attacker from fully worming into developer machines.
   • The trojanized extension delivered a persistent SSH backdoor to developer machines.

   Still unconfirmed

   • North Korean hackers are suspected of involvement in the operation.

   What to watch next

   • Official attribution of the threat actor group responsible for the supply chain breach.
   • Further remediation guidelines from Cursor and Anthropic for affected developers.
   Sources used for this update (21)

   1. arstechnica.com — Ars Technica - Serving the Technologist since 1998. News, reviews, and ...
   2. www.wired.com — WIRED - The Latest in Technology, Science, Culture and Business
   3. feedly.com — CVE-2026-86988 - Exploits & Severity
   4. 1023jack.com — Anthropic Could Go Public With A “Junk” Credit Rating. What That Means, And What Is Actually Confirmed
   5. WIRED — A Supply Chain Attack Put Malicious Anthropic Claude Extensions on Thousands of Devices
   6. Reuters — Cursor says up to 5,000 users affected by tampered Claude Code extension
   7. Microsoft — Inside a malicious Claude Code-branded extension and its persistent SSH backdoor
   8. DoublePulsar — Anthropic hacked to deliver remote access trojan to Claude developer laptops worldwide
   9. Ars Technica — Anthropic VS code extension on Cursor backdoored for nearly 12 hours
   10. latent.space — Google admits AI Mode hurts Search revenue; -15% $500B drop worst since 2004 IPO. AI Bear Market coming? — Latent Space
   11. Step Security — Trojanized Claude Code Extension Delivered Persistent SSH Backdoor to Developer Machines
   12. fastnews.team — North Korean hackers suspected in $351M crypto theft, the largest so far this year | FastNews.team
   confidence 95%