Anyone who can file an issue on your GitHub repo can now leak your CI/CD secrets. No code, no exploits, no malware. Just text in a GitHub issue body, with one HTML comment your maintainers can't see but your AI agent can.
Microsoft Threat Intelligence published the writeup this morning. The bug is in Claude Code's GitHub Action, specifically the Read tool. Anthropic patched it on May 5 in Claude Code 2.1.128, six days from disclosure to fix. That's fast and good. But the patch isn't the lesson. The lesson is what shipped in the first place, and what it tells you about every other agent stack in production right now.
What the bug actually is
Claude Code in GitHub Actions can be triggered by GitHub events. Issues, PRs, comments. The agent reads that content and decides what to do. It has tools: Bash, Read, WebFetch, GitHub APIs.
Anthropic sandboxed Bash carefully. Bubblewrap-style isolation. Environment scrubbing for subprocess paths when untrusted users could influence the workflow. The right instinct: if an attacker can steer the agent, don't let the agent's subprocess inherit your secrets.
