CVE-2025-2256 in Community Edition
Summary
by MITRE • 09/12/2025
An issue has been discovered in GitLab CE/EE affecting all versions from 7.12 before 18.1.6, 18.2 before 18.2.6, and 18.3 before 18.3.2 that could have allowed unauthorized users to render the GitLab instance unresponsive to legitimate users by sending multiple concurrent large SAML responses.
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Analysis
by VulDB Data Team • 09/12/2025
This vulnerability in GitLab CE/EE represents a significant denial of service threat that exploits the SAML authentication processing mechanism. The flaw exists in versions prior to the specified patched releases, creating a window of exposure from version 7.12 through 18.3.1. The vulnerability stems from inadequate handling of SAML responses during authentication processes, where the system fails to properly manage resource allocation when processing large SAML assertions. This issue specifically affects the authentication flow where legitimate users attempting to access the GitLab instance may encounter service disruption when the system becomes overwhelmed by concurrent large SAML responses. The technical root cause involves insufficient input validation and resource management within the SAML response processing pipeline, which allows malicious actors to craft SAML responses that consume disproportionate system resources. This vulnerability maps to CWE-400 which addresses "Uncontrolled Resource Consumption" and aligns with ATT&CK technique T1499.004 for "Endpoint Denial of Service" within the context of authentication systems.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire GitLab instance availability. When unauthorized users send multiple concurrent large SAML responses, the system experiences resource exhaustion that affects legitimate user access and authentication attempts. The attack vector requires minimal technical sophistication while delivering substantial operational consequences, making it particularly dangerous in environments where GitLab serves as a critical authentication hub for development teams and enterprise users. The vulnerability affects all versions within the specified ranges, indicating a long-standing flaw in the authentication processing logic that was not properly addressed until the respective patch releases. System administrators may observe degraded performance, authentication failures, and potential complete service unavailability during active exploitation attempts.
Mitigation strategies for this vulnerability should focus on immediate patching of affected GitLab instances to versions 18.1.6, 18.2.6, or 18.3.2 respectively. Organizations should implement rate limiting and resource monitoring for SAML authentication endpoints to detect and prevent abuse patterns. Network-level controls can be deployed to restrict SAML response sizes and implement connection throttling mechanisms. Additionally, security teams should conduct thorough review of SAML configuration settings and ensure proper authentication flow monitoring. The patch releases include specific fixes for resource consumption handling during SAML response processing, addressing the core issue of insufficient input validation and memory management. Organizations should also consider implementing authentication auditing and anomaly detection systems that can identify unusual patterns in SAML response processing that may indicate exploitation attempts. Regular security assessments of authentication mechanisms and proper access controls should be maintained to prevent unauthorized access to systems that may leverage this vulnerability for further exploitation.