A real attack attempt used a malicious AGENTS.md file placed in a developer’s Downloads folder and disguised as normal engineering notes. When an AI coding assistant opened the folder, the file instructed the agent to install malware; related compromised GitHub repositories used hidden AI-assistant hooks to trigger malicious code when opened.
In one documented case, a malicious AGENTS.md file was placed in a developer's Downloads folder and disguised as routine engineering notes. When an AI coding assistant opened that folder, it followed the embedded instructions and attempted to install function-color, a known-malicious npm package. In isolated testing, the same payload caused the Codex agent to add an unauthorized MCP server to its machine-wide configuration and run malware in more than 90% of attempts.
A related campaign, identified by JFrog, involved 42 hijacked GitHub repositories across 11 owners. These repositories contained hidden hooks in configuration files used by popular AI coding tools, including Claude, Gemini, Cursor, and Visual Studio Code. Opening an affected repository in a supported development tool could trigger a hidden .github/init.js payload, a file large enough to evade standard GitHub code search.
The attack relied on a core behavior of AI coding agents: they are built to read and act on instruction files found in the folders or repositories they open. By disguising malicious commands as ordinary engineering notes or standard project setup files, attackers exploited the trust developers place in both their tooling and their own familiar working directories. The hidden hooks were also placed in files developers rarely inspect manually, such as .claude/settings.json or .vscode/tasks.json, making the compromise easy to overlook during normal review.
These behaviors map to MITRE ATT&CK technique T1204.002 (user execution of malicious file) and T1656 (impersonation), both relevant to how trust in routine-looking files and tooling was exploited.
Mirage safely runs attacks like this one against your own team, so you find out what happens before a real adversary does.
It refers to a real case where a malicious AGENTS.md file was placed in a Downloads folder disguised as routine engineering notes, instructing an AI coding agent to install a known-malicious npm package.
JFrog found 42 hijacked GitHub repositories across 11 owners containing hidden hooks in files like .claude/settings.json and .cursor/mcp.json that could trigger a malicious .github/init.js script when opened in a supported AI coding tool.
Coding agents are designed to follow instruction files found in folders or repositories they open, which attackers exploit by disguising malicious commands as ordinary project setup notes.
The campaign reportedly includes a wiper component that activates when the stolen GitHub token is revoked, according to the key findings.
A project note can give your coding assistant orders. One AGENTS.md in Downloads looked like engineering notes, but told Codex to install the malicious function-color package. In testing, it also added an MCP server to machine-wide settings. Same trick on GitHub: 42 hijacked repos hid hooks in Claude, Gemini, Cursor, and VS Code settings. Opening one could run a hidden .github/init.js payload. Before opening a public repo in an AI coding tool, review its hidden config and task files.
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