How severe is GHSA-8q5r-mmjf-575q?

No CVSS score has been assigned to GHSA-8q5r-mmjf-575q yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-8q5r-mmjf-575q?

GHSA-8q5r-mmjf-575q affects the following packages: anthropics/claude-code-action (GitHub Actions). Ecosystems affected: GitHub Actions.

How do I fix GHSA-8q5r-mmjf-575q?

Update anthropics/claude-code-action to 1.0.74 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8q5r-mmjf-575q is resolved across your whole dependency graph.

How do I detect GHSA-8q5r-mmjf-575q in my GitHub Actions dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for anthropics/claude-code-action, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-8q5r-mmjf-575q if there is no patch (or I can't update yet)?

Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Is GHSA-8q5r-mmjf-575q actively exploited in the wild?

No public exploit code has been indexed for GHSA-8q5r-mmjf-575q yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-8q5r-mmjf-575q?

GHSA-8q5r-mmjf-575q has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 55th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-8q5r-mmjf-575q?

GHSA-8q5r-mmjf-575q is classified as OS Command Injection (CWE-78), Information Exposure (CWE-200). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was GHSA-8q5r-mmjf-575q published, and has it been updated?

GHSA-8q5r-mmjf-575q was published on June 10, 2026 and was last updated on September 15, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 GitHub Actions

Not in CISA KEV

Claude Code Action: Malicious MCP Server Configuration in PRs Enables Remote Code Execution and Secret ExfiltrationGHSA-8q5r-mmjf-575q

Fix: anthropics/claude-code-action#1066

GHSA-8q5r-mmjf-575q is a OS Command Injection vulnerability in anthropics/claude-code-action. A fix is available for anthropics/claude-code-action — see the affected versions and patch details below.

Also known asCVE-2026-47751

Published

Jun 10, 2026

Updated

Sep 15, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-8q5r-mmjf-575q.

EPSS Exploitation Probability

via FIRST.org ↗

0.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs55th percentile — riskier than 55% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

📦anthropics/claude-code-action

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects GitHub Actions packages — download data is not available via public APIs for these ecosystems.

Description

Due to the combination of checking out PR head branches (attacker-controlled), reading .mcp.json from the working directory via default setting sources, and unconditionally enabling all project MCP servers via enableAllProjectMcpServers, it was possible for an attacker who opened a PR containing a malicious .mcp.json 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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦GitHub Actions	`anthropics/claude-code-action`	all versions	1.0.74

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for anthropics/claude-code-action, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update anthropics/claude-code-action to 1.0.74 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8q5r-mmjf-575q is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Frequently Asked Questions

Due to the combination of checking out PR head branches (attacker-controlled), reading `.mcp.json` from the working directory via default setting sources, and unconditionally enabling all project MCP servers via `enableAllProjectMcpServers`, it was possible for an attacker who opened a PR containing a malicious `.mcp.json` 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 ope

O3 Security · Impact-Aware SCA

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