CVE-2021-39907 in Community Edition
Summary
by MITRE • 11/05/2021
A potential DOS vulnerability was discovered in GitLab CE/EE starting with version 13.7. The stripping of EXIF data from certain images resulted in high CPU usage.
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Analysis
by VulDB Data Team • 11/09/2021
The vulnerability identified as CVE-2021-39907 represents a denial of service weakness in GitLab Community and Enterprise editions affecting versions 13.7 and later. This issue manifests through the processing of specific image files during the EXIF data stripping operation, where the system consumes excessive computational resources. The flaw exploits the image processing pipeline within GitLab's file handling mechanisms, particularly when dealing with images that contain malformed or specially crafted EXIF metadata structures.
Technical exploitation of this vulnerability occurs when GitLab attempts to sanitize image files by removing EXIF metadata, a common security practice to prevent potential malicious data injection. The implementation contains a processing loop or recursive function that becomes inefficient when encountering certain image formats or corrupted EXIF data structures. This results in the CPU utilization reaching near 100% for extended periods, effectively rendering the GitLab instance unresponsive to legitimate user requests. The vulnerability is categorized under CWE-400 as an excessive resource consumption issue, specifically manifesting as a denial of service condition.
The operational impact of CVE-2021-39907 extends beyond simple service disruption, as it can severely affect GitLab instance availability and user productivity. Organizations relying on GitLab for version control, CI/CD pipelines, and collaboration may experience complete service unavailability during the attack window. The vulnerability affects both GitLab CE and EE editions, making it a widespread concern across the user base. Attackers can exploit this weakness by uploading specifically crafted image files that trigger the resource-intensive processing loop, potentially causing cascading failures in systems where GitLab is integrated with other services or automated workflows.
Mitigation strategies for CVE-2021-39907 include immediate patching of GitLab installations to versions that address the specific processing inefficiency in EXIF data handling. System administrators should implement image file validation and filtering at the network perimeter or application level to prevent problematic files from reaching the GitLab processing pipeline. The implementation of resource limits and process monitoring can help detect and contain the vulnerability's effects before complete service exhaustion occurs. Organizations should also consider implementing rate limiting for file uploads and automated scanning of uploaded content for known problematic patterns. This vulnerability aligns with ATT&CK technique T1499.004 for network denial of service and demonstrates the importance of proper resource management in security-critical applications. The fix typically involves optimizing the EXIF data parsing algorithm to prevent infinite loops or excessive recursion when processing malformed image metadata, ensuring that the resource consumption remains within acceptable bounds regardless of input complexity.