6:31 PM ET · Oct 30

Backdoored Claude Code extension sat in Cursor's marketplace for nearly 12 hours

A tampered build of Anthropic's Claude Code extension (versions 2.1.312 and 2.1.313) was available in Cursor's VS Code extension marketplace from about 2:27am to 1:35pm PT on Oct 29, reaching at most 5,000 users. The loader sent host details to an attacker server, added an SSH key labeled "svc-telemetry" to authorized_keys, installed persistence and tried to open a reverse SSH tunnel, though bugs mostly kept the tunnel from working without admin rights. Cursor pulled the build, shut down and rebuilt the marketplace, rotated keys and got the attacker's server taken offline. Anthropic says it didn't build or publish the package and that its own systems and official channels weren't compromised.

Source: Ars Technica

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We identified a security incident affecting a modified Claude Code VS Code extension accessed through our Cursor IDE extension marketplace, impacting at most 5,000 users. This malicious version of the extension was not developed by Anthropic. It does not impact other extensions
— Cursor (@cursor_ai) Oct 30, 2026

We’re working with Cursor on this incident, but it wasn’t a compromise of Anthropic’s systems or employee laptops. A malicious actor used access to Cursor’s marketplace to publish a tampered copy of the Claude Code extension, which we didn’t build or publish.
— Felix Rieseberg (@felixrieseberg) Oct 30, 2026

‼️ Anthropic's official Claude Code extension was distributed with an SSH backdoor via Cursor's marketplace. A trojanized update (v2.1.313) targeted up to 5,000 users, according to Cursor. How attackers pushed it under the legitimate extension's identity remains unclear.
— The Hacker News (@TheHackersNews) Oct 30, 2026

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Backdoored Claude Code extension sat in Cursor's marketplace for nearly 12 hours

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