Researchers show AI coding agents can be hijacked via malicious agents.md files
Researchers at Forever Security discovered a security vulnerability where AI coding agents can be manipulated by malicious instruction files. They found a rogue AGENTS.md file in a customer's Downloads folder that tricked an agent into installing a malicious npm package named 'function-color.' The study demonstrates that because agents automatically load instructions from their working…
Key points
- Malicious AGENTS.md files in Downloads folders can trick AI agents into running unauthorized commands.
- Tests showed a 90% success rate for hijacking OpenAI Codex and 50% for leaking Claude Code tokens.
- Researchers advise users to avoid running AI coding agents from the ~/Downloads directory to prevent this risk.
The team reproduced the attack against OpenAI Codex, achieving a 90% success rate with a harmless payload. They also tested a related technique against Claude Code, using a malicious CLAUDE.md file to redirect API traffic and leak OAuth tokens, which succeeded in roughly 50% of tests. The vulnerability exploits standard browser behavior, where Chrome, Edge, and Firefox save downloads to the ~/Downloads folder by default without prompting the user for a location.
Forever Security notes that many users run agents from their Downloads folders, with Claude Code alone launching over 1,300 sessions from that location. The researchers emphasize that this is not a bug in the AI models but a result of intended behavior. They advise users to avoid using ~/Downloads as a working directory, keep agent scopes narrow, and review unfamiliar instruction files before execution.
AI coding agents hijacked using AGENTS.md file in Downloads folder
bleepingcomputer.com · 25 October 2026
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