Securing CI/CD in an agentic world: Claude Code GitHub action case

This Microsoft Threat Intelligence blog post details a vulnerability discovered in Anthropic's Claude Code GitHub Action, where the Read tool could access sensitive /proc files (like /proc/self/environ) and expose workflow secrets, including the ANTHROPIC_API_KEY. The issue arose because the Read tool operated outside the Bubblewrap sandbox used for Bash, and a prompt injection could bypass safety filters and GitHub's secret scanner by laundering the key. Anthropic mitigated this in Claude Code 2.1.128 by blocking access to sensitive /proc files. The post provides actionable hardening guidance, including applying the "Agents Rule of Two" (never combine untrusted input, secret access, and external communication in one workflow), enforcing least privilege, hardening system prompts, and monitoring for suspicious activity. It also maps the attack to MITRE ATLAS techniques and emphasizes that AI workflows processing untrusted content must be treated as high-risk. 

https://www.microsoft.com/en-us/security/blog/2026/06/05/securing-ci-cd-in-agentic-world-claude-code-github-action-case

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