CVE-2023-27581 in github-slug-action
Summary
by MITRE • 03/13/2023
github-slug-action is a GitHub Action to expose slug value of GitHub environment variables inside of one's GitHub workflow. Starting in version 4.0.0` and prior to version 4.4.1, this action uses the `github.head_ref` parameter in an insecure way. This vulnerability can be triggered by any user on GitHub on any workflow using the action on pull requests. They just need to create a pull request with a branch name, which can contain the attack payload. This can be used to execute code on the GitHub runners and to exfiltrate any secrets one uses in the CI pipeline. A patched action is available in version 4.4.1. No workaround is available.
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Analysis
by VulDB Data Team • 03/14/2023
The github-slug-action vulnerability represents a critical security flaw in the GitHub Actions ecosystem that enables arbitrary code execution and secret exfiltration through insecure handling of pull request branch names. This vulnerability exists in versions 4.0.0 through 4.4.0 of the action, where the developers failed to properly sanitize the github.head_ref parameter that is used to determine the branch name for pull requests. The flaw allows any GitHub user to craft malicious branch names containing payload code that gets executed within the CI/CD pipeline environment. This represents a severe privilege escalation vulnerability since it enables attackers to execute arbitrary commands on GitHub runners with the same permissions as the workflow itself. The vulnerability is particularly dangerous because it requires no special privileges to exploit - any user can create a pull request with a malicious branch name and trigger the vulnerability. The technical implementation flaw falls under CWE-74, which describes improper neutralization of special elements used in data queries, specifically in how the action processes the head_ref parameter without adequate sanitization. This vulnerability directly maps to ATT&CK technique T1059.001 for command and scripting interpreter and T1537 for exfiltration through data staging. The impact extends beyond simple code execution to include complete compromise of CI/CD pipelines where attackers can access and exfiltrate secrets, environment variables, and other sensitive data that may be present in the runner environment. The vulnerability affects any workflow that utilizes the affected action on pull requests, making it broadly applicable across GitHub organizations that rely on automated workflows for code integration. The exploitation mechanism relies on the fact that GitHub Actions automatically populates github.head_ref with the source branch name of pull requests, and when this value is passed directly into shell commands or other execution contexts without proper validation, it creates a path for command injection attacks. The lack of available workarounds means organizations must upgrade to version 4.4.1 or later to remediate this vulnerability, as no other mitigation strategies exist for the specific flaw in the action's implementation. This vulnerability demonstrates the critical importance of input validation in CI/CD tooling and highlights how seemingly innocuous parameters can become attack vectors when not properly sanitized in automated environments. The remediation process requires updating the action reference in all affected workflows to use version 4.4.1 or higher, which contains the necessary patches to properly escape and validate the head_ref parameter before processing. Organizations should conduct immediate audits of their GitHub Actions workflows to identify all instances of the vulnerable action and ensure proper patching to prevent potential compromise of their automated build and deployment pipelines. The vulnerability also underscores the need for security reviews of third-party GitHub Actions, as this flaw was present in a widely-used action that many organizations incorporate into their development workflows without sufficient security assessment of the underlying implementation.