PatchSiren cyber security CVE debrief
CVE-2026-47751 anthropics CVE debrief
CVE-2026-47751 is a vulnerability in Claude Code Action, a GitHub action that runs Claude Code on GitHub pull requests and issues. Prior to version 1.0.74, the action checked out attacker-controlled pull request head branches, read .mcp.json from the working directory via default setting sources, and unconditionally enabled all project MCP servers. This allowed an attacker who opened a pull request containing a malicious .mcp.json file to achieve arbitrary code execution on the GitHub Actions runner and exfiltrate secrets available to the workflow. The issue was fixed in version 1.0.74, which restores .claude/ and .mcp.json from the pull request base branch before the CLI runs. Users of Claude Code Action, especially those who use the action in privileged workflows or with sensitive data, should be aware of this vulnerability and take steps to protect themselves.
- Vendor
- anthropics
- Product
- claude-code-action
- CVSS
- MEDIUM 5.3
- CISA KEV
- Not listed in stored evidence
- Original CVE published
- 2026-07-16
- Original CVE updated
- 2026-07-16
- Advisory published
- 2026-07-16
- Advisory updated
- 2026-07-16
Who should care
Users of Claude Code Action, especially those who use the action in privileged workflows or with sensitive data, should be aware of this vulnerability and take steps to protect themselves. This includes updating to version 1.0.74 or later, reviewing and restricting access to workflows that use Claude Code Action, monitoring workflows for suspicious activity, and using secure practices when working with sensitive data in workflows.
Technical summary
The vulnerability in Claude Code Action allowed an attacker to execute arbitrary code on the GitHub Actions runner by including a malicious .mcp.json file in a pull request. This was possible because the action checked out attacker-controlled pull request head branches and enabled all project MCP servers by default. The issue was fixed in version 1.0.74, which restores .claude/ and .mcp.json from the pull request base branch before the CLI runs. The vulnerability has a CVSS score of 5.3 and a severity of MEDIUM.
Defensive priority
Medium
Recommended defensive actions
- Update Claude Code Action to version 1.0.74 or later
- Review and restrict access to workflows that use Claude Code Action
- Monitor workflows for suspicious activity
- Use secure practices when working with sensitive data in workflows
- Review compensating controls for exposed systems while remediation is scheduled and verified
- Check relevant monitoring, detection, and logs for exposed assets that need extra review
- Track exceptions, retest remediated assets, and close the item only after evidence is documented
Evidence notes
The CVE record was published on 2026-07-16T17:16:57.357Z and has not been modified since then. The NVD entry is currently Awaiting Analysis. There is limited information available about the vulnerability, and defenders should verify the affected scope and severity with the vendor. The vulnerability is in Claude Code Action, a GitHub action that runs Claude Code on GitHub pull requests and issues. Prior to version 1.0.74, the action checked out attacker-controlled pull request head branches, read .mcp.json from the working directory via default setting sources, and unconditionally enabled all project MCP servers.
Official resources
AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-16T17:16:57.357Z and has not been modified since then.