Poisoned Claude Code VS Code Extension Planted SSH Backdoor, Affecting Up to 5,000 Users

The official Claude Code VS Code extension fell victim to a supply chain attack: version 2.1.313, self-identified as anthropic.claude-code on the Open VSX registry, was found to contain malicious code. Cursor officially confirmed that the trojanized version appeared in its extension marketplace between 09:27–20:35 UTC on October 29, potentially affecting up to 5000 users across platforms including macOS ARM64. What makes this incident notable is that the poisoned package was not a counterfeit plugin but a tampered version of the official extension itself, exposing trust risks in the extension distribution chain.

Confirmed

• Cursor's official notice: the malicious anthropic.claude-code v2.1.313 was listed on its marketplace from 09:27–20:35 UTC on October 29, with an estimated impact of up to 5000 users
• The malicious version was discovered by security firm Phorion; 66 lines of malicious loader code were inserted in extension.js ahead of the legitimate code
• Once activated, the malicious code adds the attacker's public key to users' SSH configuration, attempts to enable the local SSH service, and establishes a reverse connection
• Phorion's analysis indicates the backdoor has cross-platform persistence capabilities, covering macOS, Linux, and Windows
• Cursor took down its entire extension marketplace that afternoon and coordinated remediation with relevant parties

Why It Matters

• The poisoned package carried the official identifier rather than being an obvious counterfeit, making it nearly impossible for ordinary users to detect—highlighting supply chain trust issues in extension registries and IDE plugin marketplaces
• The backdoor targets SSH configuration and persistence mechanisms, so its potential impact extends well beyond a single IDE environment; affected users should check their SSH configuration for unknown public keys

2026-10-30 ~ 2026-10-30 · 8 related posts

• Official Claude Code VS Code Extension Trojanized: v2.1.313 Plants SSH Backdoor — jd_pressman · 2026-10-30
• Cursor pulls plugin marketplace after malicious Claude Code extension hits up to 5,000 users — EricBuess · 2026-10-30
• [source] Cursor confirms trojanized Claude Code v2.1.313 extension hit up to 5,000 users with SSH backdoor — cyb3rops · 2026-10-30
• Claude Code VS Code Extension Had a Trojan Today, Claims Researcher, Zero Coverage — evilsocket · 2026-10-30
• Claude Code OpenVSX extension backdoored, tied to Anthropic employee's publisher account — banteg · 2026-10-30

3 near-duplicate retellings: DanielLockyer · jedisct1 · banteg