A concerning security weakness within GitLab's Continuous Integration and Continuous Deployment (CI/CD) pipeline infrastructure has been uncovered, highlighting a stealthy method for attackers to compromise pipeline execution environments. Security researcher 'sellathechemist' detailed their findings on Mastodon, demonstrating how pipeline tokens – crucial credentials granting access to repositories and deployment environments – can be exposed through GitLab's API without requiring elevated permissions.

The Core Vulnerability: Silent Token Exposure

The researcher demonstrated that an attacker, possessing only minimal access (e.g., Guest or Reporter role) to a project, can exploit the GitLab API to retrieve the job_token associated with a pipeline. Crucially, this action bypasses the typical permission checks (read_build/read_job) that would normally restrict access to such sensitive information:

GET /api/v4/projects/:id/jobs/:job_id

The API endpoint above returns detailed information about a specific job, including thetokenfield – the very pipeline job token. This occurs even if the user lacks the necessaryread_buildpermission, effectively leaking a high-privilege credential to lower-privileged or even unauthorized users.

Why This Matters: The Attack Implications

This exposure creates a severe attack vector:

  1. Pipeline Impersonation: An attacker capturing a job token can impersonate a legitimate CI/CD pipeline. This allows them to potentially execute malicious code within the trusted pipeline context, bypassing security controls designed to vet external contributions.
  2. Unauthorized Repository Access: Pipeline tokens often possess significant permissions, including read_repository and write_repository. Leaked tokens grant attackers the same level of access, enabling them to clone private repositories, inject malicious code, or exfiltrate sensitive intellectual property.
  3. Supply Chain Compromise: Malicious actors could manipulate the build process, injecting backdoors or vulnerable dependencies into artifacts deployed downstream, compromising the entire software supply chain originating from the affected project.

Researcher's Mitigation Advice and GitLab's Stance

'sellathechemist' strongly advises GitLab users to immediately revoke any pipeline tokens suspected of exposure and critically re-evaluate the permissions granted to these tokens. Restricting pipeline tokens to the absolute minimum necessary permissions is paramount.

As of the disclosure, GitLab has not publicly acknowledged this specific API behavior as a vulnerability or announced plans to modify the permission checks surrounding the /jobs/:job_id endpoint. This underscores the importance of proactive security measures by development and operations teams relying on GitLab CI/CD. The stealthy nature of this exposure – leaking credentials without triggering permission denials – makes it particularly dangerous and difficult to detect through standard auditing.

This discovery serves as a stark reminder of the complex attack surfaces inherent in CI/CD systems and the critical need for continuous scrutiny of the permissions granted to automated processes. Developers and platform engineers must assume a zero-trust posture towards pipeline tokens, rigorously limiting their scope and monitoring for anomalous usage, especially given the potential for silent credential leakage demonstrated here.

(Source: Mastodon post by @sellathechemist, July 19, 2024)