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Findings

CVE-2026-47751

Claude Code Action: Malicious MCP Server Configuration in PRs Enables Remote Code Execution and Secret Exfiltration

Published Jun 10, 2026 · corrected/updated Sep 15, 2026 · evidence confidence high

Due to the combination of checking out PR head branches (attacker-controlled), reading from the working directory via default setting sources, and unconditionally enabling all project MCP servers via , it was possible for an attacker who opened a PR containing a malicious file to achieve arbitrary code execution on the GitHub Actions runner. This could lead to exfiltration of secrets available to the workflow (such as API keys and tokens) when a privileged user triggered the Claude action on the PR. Exploiting this required the ability to open a pull request against a repository using the claude-code-action and a privileged user or automatic trigger to invoke the action on that PR. Users pinned to a vulnerable version of claude-code-action are advised to update to the latest version. Users referencing anthropics/claude-code-action@v1, anthropics/claude-code-action@beta, anthropics/claude-code-action@main, or other non-pinned tags will have received this fix already Claude Code thanks hackerone.com/reptou for reporting this issue.

Grounded briefings

Catalog interpretations for three audiences. Each brief cites ingested metadata and the original advisories below. They are not independent research and they do not invent exploit steps.

Executive

CVE-2026-47751 is a unknown public vulnerability record for this product. It is not currently listed in the CISA Known Exploited catalog. Check the linked vendor or CERT advisories for patch status. This summary is a catalog interpretation of the ingested metadata and cites the original advisories below.

System administrator

Identify whether this product is in your estate, then compare installed versions with the affected ranges. Affected packages or ranges on record: anthropics/claude-code-action (0 → 1.0.74). Check the linked vendor or CERT advisories for patch status. Prefer the vendor or distribution advisory linked in Sources before changing production systems. This is a catalog interpretation, not a runbook.

Security analyst

Signals on file: no CVSS/EPSS yet. It is not currently listed in the CISA Known Exploited catalog. Weakness classes: CWE-200, CWE-78. Sources contributing to this record: cve_org, github, osv. Public exploit references, when present, are outbound links only and are not proof of active exploitation. This is a catalog interpretation of stored metadata.

Exploitation and remediation

  • Exploitation evidence

    Not listed as known exploited in CISA KEV. Not in CISA KEV or VulnCheck KEV.

  • Patch and remediation

    No required-action text is stored yet. Use the vendor or CERT links in Sources for patch availability.

  • Safe detection guidance

    Compare installed versions with the affected ranges below and verify the advisory from the original publisher. This site stores metadata and outbound links only; it does not ship exploit code or proof-of-concept payloads.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Jun 10, 2026 · GitHub Advisory Database

    Detected

    Due to the combination of checking out PR head branches (attacker-controlled), reading from the working directory via default setting sources, and unconditionally enabling all project MCP servers via , it was possible for an attacker who opened a PR containing a malicious file to achieve arbitrary code execution on the GitHub Actions runner. This could lead to exfiltration of secrets available to

  2. Sep 15, 2026 · GitHub Advisory Database

    Fix available

    anthropics/claude-code-action fixed in 1.0.74

  3. Sep 15, 2026 · GitHub Advisory Database

    Fix available

    anthropics/claude-code-action fixed in 1.0.74

  4. Sep 15, 2026 · GitHub Advisory Database

    Updated

    Due to the combination of checking out PR head branches (attacker-controlled), reading from the working directory via default setting sources, and unconditionally enabling all project MCP servers via , it was possible for an attacker who opened a PR containing a malicious file to achieve arbitrary code execution on the GitHub Actions runner. This could lead to exfiltration of secrets available to

Affected

  • GitHub Actions anthropics/claude-code-action0 → 1.0.74

Sources

References