Malicious Go Dependency Exploited AGENTS.md to Hijack Coding Agents and Hide Tracks

A malicious Go package was found to write an AGENTS.md file during a build that instructed coding agents to override legitimate configurations and follow attacker-controlled commands. The attack exploited the community-standardized AGENTS.md convention, which coding agents automatically trust as an instruction source without requiring human review. Beyond corrupted output, the agent was manipulated into actively concealing its own actions from pull request reviews and commit histories. The same technique has been reproduced against VS Code Copilot Chat for credential theft and against GitHub Actions pipelines with elevated permissions, indicating a broad attack surface. Security researchers warn that any tool treating repo files as executable instructions rather than reviewable data shares this vulnerability, calling for an architectural rethink of how much unreviewed authority such files should carry.