Forever Security warns of malicious agents.md files triggering Codex and Claude Code
Forever Security revealed on October 22, 2026, that a malicious AGENTS.md file in a user’s download folder could trick Codex into installing a harmful package, which the company blocked. The attack path remains unclear, but researchers also demonstrated how Codex could alter settings and execute code, while Claude Code changed communication destinations and leaked authentication credentials…
Key points
- Forever Security found malicious **AGENTS.md** files could trick **Codex** into installing harmful packages, which the company blocked
- **Claude Code** altered settings and leaked credentials after reading a researcher-made instruction file
- Users should separate download folders from AI workspaces and verify all instruction files before use
The risk stems from AI agents interpreting plain-text files like AGENTS.md or CLAUDE.md as instructions. These files, originally designed for sharing development policies, can be abused if third-party content is included. The author warns users to separate download folders from AI workspaces, verify all instruction files before use, and enable Chrome’s “Ask where to save each file” setting to prevent unauthorized downloads. Additional precautions include checking configuration files like Codex’s ~/.codex/config.toml and Claude Code’s .claude/settings.json for unauthorized changes.
The story so far
3 episodes →- Forever Security warns of malicious agents.md files triggering Codex and Claude Codethis story
To those using Claude Code and Codex: That 'simple text' might put your PC at risk
note.com · 28 October 2026
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