CVE-2021-22214 in Community Edition
Summary
by MITRE • 06/08/2021
When requests to the internal network for webhooks are enabled, a server-side request forgery vulnerability in GitLab CE/EE affecting all versions starting from 10.5 was possible to exploit for an unauthenticated attacker even on a GitLab instance where registration is limited
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Analysis
by VulDB Data Team • 06/12/2021
The vulnerability identified as CVE-2021-22214 represents a critical server-side request forgery flaw in GitLab Community Edition and Enterprise Edition products. This security weakness specifically impacts installations where internal network webhook requests are enabled, creating a pathway for unauthorized exploitation. The vulnerability exists in all GitLab versions beginning with 10.5, making it a long-standing issue that affects a substantial portion of deployed instances. The flaw is particularly concerning because it allows unauthenticated attackers to leverage this vulnerability even on GitLab instances where user registration is restricted, effectively bypassing access controls that should otherwise protect the system.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization within GitLab's webhook processing mechanisms. When webhook functionality is enabled for internal network communications, the application fails to properly validate or sanitize the URLs used for these requests. This allows an attacker to craft malicious webhook URLs that could potentially target internal systems, bypassing normal network segmentation and access controls. The vulnerability operates at the application layer where external requests are made to internal resources, creating a classic server-side request forgery scenario that maps to CWE-918. The flaw demonstrates poor separation of concerns in the application's architecture, where external input directly influences internal network operations without proper security boundaries.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it enables attackers to perform reconnaissance and potentially gain access to internal systems that should remain isolated from external networks. An attacker could exploit this vulnerability to probe internal network services, potentially identifying running applications, open ports, and system configurations that would normally be hidden from external view. This reconnaissance capability significantly increases the risk profile of affected GitLab installations, as it provides attackers with valuable information for further exploitation. The vulnerability affects the confidentiality and integrity of the system by allowing unauthorized access to internal resources that should remain protected, and it can also compromise the availability of internal services if the attacker uses the vulnerability to perform denial-of-service attacks against internal systems. This aligns with ATT&CK technique T1071.004 for Application Layer Protocol and T1046 for Network Service Scanning.
Organizations should implement immediate mitigations to address this vulnerability, including disabling webhook functionality for internal networks when such access is not required, implementing proper URL validation and sanitization measures, and restricting network access to internal systems through proper firewall rules and network segmentation. The most effective immediate solution involves configuring GitLab instances to disable internal webhook functionality or to ensure that webhook URLs are properly validated against a known whitelist of acceptable destinations. Additionally, organizations should consider implementing network-level protections such as firewalls that restrict outbound connections from GitLab servers to internal networks, preventing the exploitation of this vulnerability even if other mitigations fail. Regular security audits and monitoring of webhook usage should also be implemented to detect potential exploitation attempts. The vulnerability highlights the importance of following secure coding practices and implementing proper input validation as outlined in the OWASP Top Ten and NIST Cybersecurity Framework.