
Trojanized Claude Code Extension: How a Single Cursor Marketplace Update Backdoored 5,000 Developer Machines
On October 29, 2026, a trojanized version of Anthropic's official Claude Code extension (version 2.1.313) was distributed through Cursor's IDE marketplace under the legitimate publisher identity anthropic.claude-code. Between approximately 2:27 a.m. and 1:35 p.m. PT, up to 5,000 developers auto-updated to the malicious build, which injected a 66-line JavaScript loader to plant an attacker-controlled SSH key labeled "svc-telemetry," establish a reverse tunnel to 134.209.82.225, install cross-platform persistence, and beacon host reconnaissance data—including environment variable names referencing cloud credentials—over unencrypted HTTP to port 8099. This incident reflects a sharp escalation in software supply-chain attacks targeting AI developer tooling. As agentic AI extensions gain privileged access to developer workstations and cloud credential stores, attackers are exploiting marketplace trust relationships and auto-update mechanisms to achieve persistent footholds at the earliest stage of the software development lifecycle, compressing the window between initial compromise and credential exposure.
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