Check Five Things Before You Install an Agent Plugin

The Decision Brief

If your team uses AI agents, someone will soon ask to install a plugin for one, and DeepSeek is about to make that easier. The company says its open-source Harness agent already has about 35,000 community plugins and is building an official store. Its own safety notice says the software has not undergone a security audit and tells users to review plugins before allowing them to run, without saying how.

We read Harness's install documentation and the disclosures on two 2026 campaigns against agent add-ons. In one, an MCP server answered three ordinary requests cleanly, then rewrote its instructions to send the agent after SSH keys and cloud credentials. In the other, researchers found that Claude Code, Gemini and ChatGPT surfaced malicious repositories without being shown a link. We did not test any plugin ourselves, and no source we found documents a malicious Harness plugin so far.

The full piece sets out a proposed five-point check, from what a plugin can reach once loaded to whether a change after approval would show, and a one-page approval record to keep for every request.

The evidence, the five checks and the approval record are below for PRO members. View PRO plans, $10 monthly or $99 annually.