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Forever Security traces Codex malware attempt to planted AGENTS.md

October 26, 2026 at 02:09 EDT

Security
AI Agents

Forever Security says it traced a blocked attempt to install the malicious npm package function-color on a customer's machine to an AGENTS.md file in the user's Downloads folder. In controlled tests, Codex followed the planted instructions in more than 90% of attempts; researchers also demonstrated a separate credential-routing attack against Claude Code.

OCT 22 · AGENT SECURITY

A downloaded instruction file steered Codex

A planted AGENTS.md in Downloads guided a coding agent toward a malware install. In controlled tests, Codex followed the attack path in more than 90% of attempts.

Reported success in controlled tests

Each segment represents 10 percentage points; Codex is shown at the 90% lower bound.

Codex · 90%+

Claude Code · ~50%

The tests used different attack paths; the rates are not a direct product comparison.

How the attack path works

Web page

Saves an instruction file

→

Downloads folder

Agent starts in that directory

→

Agent instructions

Change configuration and attempt install

What the tests establish

The original file's arrival path was unknown. Most test runs used a harmless calculator stand-in; the real malicious package was run once in an isolated virtual machine.

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