Supply chain attack backdoors Anthropic's Claude extension on Cursor

· Tech

A supply-chain attack planted malicious code in Anthropic's Claude extension distributed through Cursor, leaving it backdoored for nearly 12 hours. WIRED reported the tainted extension reached thousands of devices, and that flawed code in it prevented the attacker from fully worming into some 5,000 developer machines. It is still unknown how attackers gained access to Anthropic's verified Cursor account. The incident highlights the exposure created by developer tool marketplaces, where a verified publisher account becomes a direct route into the machines of the engineers building software on top of AI coding tools.

Why it matters：AI coding tools sit directly inside developer machines, so a compromise of a verified publisher account shows how quickly a marketplace trust model can become an enterprise-wide security problem.

Key points

  • The extension was backdoored for nearly 12 hours.
  • Tainted code reached thousands of devices, with flawed attacker code limiting the spread to about 5,000 developer machines.
  • How attackers accessed Anthropic's verified Cursor account remains unknown.

Sources (original reporting)

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