CVE-2021-39868 in Community Edition
Summary
by MITRE • 10/04/2021
In all versions of GitLab CE/EE since version 8.12, an authenticated low-privileged malicious user may create a project with unlimited repository size by modifying values in a project export.
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Analysis
by VulDB Data Team • 10/08/2021
The vulnerability identified as CVE-2021-39868 represents a critical access control flaw within GitLab Community Edition and Enterprise Edition platforms. This issue affects all versions starting from 8.12, making it a long-standing weakness that has persisted across multiple releases. The vulnerability specifically targets the project export functionality, which is typically used for backing up or migrating repositories. The flaw allows an authenticated user with minimal privileges to manipulate the export process in a manner that bypasses normal repository size limitations. This represents a significant escalation of privileges as it enables low-privileged users to circumvent built-in resource management controls that are designed to prevent excessive storage consumption. The vulnerability falls under the category of improper access control as defined by CWE-285, where the system fails to properly enforce access restrictions on repository operations.
The technical exploitation of this vulnerability occurs through manipulation of project export parameters, specifically targeting the mechanisms that control repository size limits during export operations. When a malicious user creates a project and subsequently initiates an export process, they can modify internal values that govern the export behavior to effectively remove or bypass the repository size constraints. This manipulation exploits the lack of proper input validation and parameter sanitization within the export functionality. The flaw essentially allows the user to create a project that appears to be within normal size limits but actually contains unlimited data storage, effectively creating a backdoor for resource exhaustion attacks. The vulnerability demonstrates poor input validation practices and inadequate parameter checking, which are core elements of CWE-20 and CWE-77.
The operational impact of this vulnerability extends far beyond simple privilege escalation, as it creates potential for significant resource exhaustion and system instability. An attacker with low-privileged access can leverage this flaw to consume excessive storage space on the GitLab server, potentially leading to denial of service conditions for other legitimate users. The unlimited repository size capability could be used to fill storage volumes, causing cascading failures in the GitLab infrastructure and affecting other projects hosted on the same platform. This vulnerability undermines the fundamental security model of GitLab's resource management and could enable attackers to disrupt service availability or compromise the integrity of the entire GitLab instance. The impact is particularly severe in multi-tenant environments where multiple projects share the same storage infrastructure. According to ATT&CK framework, this vulnerability maps to T1078.004 (Valid Accounts) and T1499.004 (Resource Hijacking) as it enables unauthorized resource consumption through legitimate access channels.
Mitigation strategies for CVE-2021-39868 should focus on immediate patching of affected GitLab installations to the latest secure versions that address the export parameter validation issues. Organizations should implement strict monitoring of project export activities and establish automated alerts for unusual export behavior that might indicate exploitation attempts. Network segmentation and access controls should be reinforced to limit the scope of potential damage from compromised low-privileged accounts. Regular security audits should verify that repository size limits are properly enforced and that no unauthorized modifications to export parameters have occurred. System administrators should also consider implementing additional storage quotas and monitoring mechanisms that can detect and prevent excessive usage patterns. The vulnerability highlights the importance of proper parameter validation and input sanitization in web applications, reinforcing the need for comprehensive security testing including penetration testing and code review processes to identify similar issues in other components of the GitLab platform.