Tampered Claude Code extension version 2.1.313 on Open VSX planted SSH backdoor

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Phorion researchers found that a tampered build of Anthropic's Claude Code extension for VS Code-compatible editors, version 2.1.313, was published on Open VSX and planted an SSH backdoor on developers' machines. Microsoft's Visual Studio Marketplace never carried the compromised extension. Users of Open VSX-based editors should check for this version; remediation steps need checking in the supplier advisory.

Digest of 2026-10-31

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