CVE-2020-5415 in Concourse
Summary
by MITRE
Concourse, versions prior to 6.3.1 and 6.4.1, in installations which use the GitLab auth connector, is vulnerable to identity spoofing by way of configuring a GitLab account with the same full name as another user who is granted access to a Concourse team. GitLab groups do not have this vulnerability, so GitLab users may be moved into groups which are then configured in the Concourse team.
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Analysis
by VulDB Data Team • 11/08/2020
The vulnerability identified as CVE-2020-5415 affects Concourse CI/CD platform versions prior to 6.3.1 and 6.4.1 when utilizing the GitLab authentication connector. This represents a critical identity spoofing vulnerability that undermines the integrity of user authentication mechanisms within the platform. The flaw specifically manifests when administrators configure Concourse teams to grant access to users authenticated through GitLab, creating a scenario where malicious actors can exploit the authentication flow to impersonate legitimate users.
The technical root cause of this vulnerability stems from how Concourse processes user identification when using GitLab authentication. The system relies on the full name field from GitLab user profiles to establish user identity within Concourse teams. When two users possess identical full names in GitLab, the authentication system cannot properly distinguish between them during the team access assignment process. This creates a race condition where the system may incorrectly map a user account to the wrong individual, effectively allowing unauthorized access through identity spoofing attacks.
This vulnerability directly maps to CWE-287 which addresses improper authentication issues, and aligns with ATT&CK technique T1078.004 for valid accounts, as it exploits legitimate authentication mechanisms to gain unauthorized access. The operational impact of this vulnerability extends beyond simple unauthorized access, as it can enable attackers to execute malicious pipeline operations, modify sensitive configuration settings, or manipulate build artifacts within Concourse teams that they should not have access to. The risk is particularly elevated in environments where Concourse is used for production deployments and security-sensitive operations.
Organizations utilizing Concourse with GitLab authentication should immediately implement mitigations including upgrading to versions 6.3.1 or 6.4.1 where this vulnerability has been patched. Alternative approaches include configuring Concourse to use GitLab groups rather than individual user accounts for team membership, as group-based authentication is not vulnerable to this particular flaw. Additionally, administrators should implement additional verification measures such as requiring unique email addresses for GitLab accounts or implementing custom attribute mapping that excludes the full name field from authentication decisions. The vulnerability demonstrates the importance of proper identity management in CI/CD platforms and highlights the need for robust authentication validation mechanisms to prevent such spoofing attacks in automated deployment environments.