CVE-2018-20500 in Community Edition
Summary
by MITRE
An insecure permissions issue was discovered in GitLab Community and Enterprise Edition 9.4 and later but before 11.4.13, 11.5.x before 11.5.6, and 11.6.x before 11.6.1. The runner registration token in the CI/CD settings could not be reset. This was a security risk if one of the maintainers leaves the group and they know the token.
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Analysis
by VulDB Data Team • 09/21/2023
The vulnerability identified as CVE-2018-20500 represents a critical access control flaw in GitLab's continuous integration and deployment infrastructure. This issue affected multiple versions of GitLab Community and Enterprise Edition, specifically targeting the CI/CD settings where runner registration tokens are managed. The flaw stems from inadequate permission controls that prevent administrators from properly resetting these tokens when team members leave projects or organizations. The vulnerability is classified under CWE-284 which deals with improper access control, specifically in the context of insufficient privileges for administrative functions within software systems.
The technical implementation of this vulnerability allows for persistent unauthorized access through the exploitation of a missing reset functionality for CI/CD runner tokens. When maintainers or team members with access to CI/CD settings leave a project, they retain knowledge of the registration tokens that grant access to the GitLab runners. This creates a persistent security risk where former employees or compromised accounts can continue to access and potentially abuse the CI/CD infrastructure. The vulnerability exists because the system does not enforce proper token rotation mechanisms that should occur when user access rights change, particularly when individuals lose their legitimate access to projects.
The operational impact of this vulnerability extends beyond simple access control breaches to encompass potential supply chain attacks and code execution compromises. Attackers who obtain runner registration tokens can potentially execute malicious code on the CI/CD runners, which may lead to data exfiltration, infrastructure compromise, or further lateral movement within the organization's development environment. This risk is particularly severe in enterprise environments where CI/CD pipelines often have access to production systems, databases, and sensitive infrastructure components. The vulnerability aligns with ATT&CK technique T1078 which covers valid accounts and privilege escalation through legitimate system access.
Organizations should immediately implement the mitigations provided in the patched versions of GitLab, specifically upgrading to versions 11.4.13, 11.5.6, or 11.6.1. The recommended approach involves establishing proper token lifecycle management procedures including regular token rotation, implementing automated access revocation when users leave projects, and ensuring that CI/CD runner tokens are not shared across multiple projects unnecessarily. Security teams should also implement monitoring for unauthorized access attempts to CI/CD settings and establish audit trails for token modifications. Additionally, organizations should review their overall CI/CD security posture, including implementing least privilege principles for runner access and ensuring that sensitive tokens are properly secured in configuration management systems. The vulnerability demonstrates the importance of proper access control implementation in DevOps environments where automation and continuous deployment systems must maintain strict security boundaries to prevent unauthorized access to critical infrastructure components.