CVE-2026-47751
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Arbitrary Code Execution in Claude Code Action via Malicious .mcp.json

Publication date: 2026-07-16

Last updated on: 2026-07-16

Assigner: GitHub, Inc.

Description
Claude Code Action is a general-purpose GitHub action that runs Claude Code on GitHub pull requests and issues. Prior to 1.0.74, because 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 via enableAllProjectMcpServers, an attacker who opened a pull request containing a malicious .mcp.json file could achieve arbitrary code execution on the GitHub Actions runner and exfiltrate secrets available to the workflow (such as API keys and tokens) when a privileged user or an automatic trigger invoked the Claude action on the pull request. This issue is fixed in version 1.0.74, which restores .claude/ and .mcp.json from the pull request base branch before the CLI runs.

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Meta Information

Published
2026-07-16
Last Modified
2026-07-16
Generated
2026-07-16
AI Q&A
2026-07-16
EPSS Evaluated
N/A
NVD
CVE-2026-47751
EUVD
EUVD-2026-44952

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
anthropic claude-code-action to 1.0.74 (exc)
github claude_code_action to 1.0.74 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-200 The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
CWE-78 The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.

Attack-Flow Graph

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Executive Summary

This vulnerability exists in the Claude Code Action GitHub workflow prior to version 1.0.74. It allows an attacker to execute arbitrary code on the GitHub Actions runner by submitting a malicious .mcp.json file in a pull request. The action automatically reads this file from the repository and enables all project MCP servers without restriction.

Detection Guidance

This vulnerability is specific to the GitHub Actions workflow environment and cannot be directly detected on a local network or system. The issue occurs when the claude-code-action runs in a GitHub Actions runner and processes untrusted pull request branches. To detect if your repository uses a vulnerable version of the action, check the workflow files for references to versions prior to 1.0.74. Look for lines like 'uses: anthropics/[email protected]' or earlier in your GitHub Actions YAML files.

Impact Analysis

If you use this GitHub action in your workflows, an attacker could gain control of your CI/CD pipeline by submitting a pull request with a malicious .mcp.json file. This could lead to theft of secrets like API keys or tokens that the workflow has access to.

Compliance Impact

This vulnerability could lead to unauthorized access and data exfiltration, violating compliance requirements for GDPR (data protection) and HIPAA (health information security). Unauthorized code execution in CI/CD pipelines may result in data breaches and non-compliance with security controls.

Mitigation Strategies

Update the Claude Code Action to version 1.0.74 or later to address the vulnerability. Ensure workflows no longer use untrusted .mcp.json files from pull request head branches.

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