CVE-2021-22220 in GitLab
Summary
by MITRE • 06/09/2021
An issue has been discovered in GitLab affecting all versions starting with 13.10. GitLab was vulnerable to a stored XSS in blob viewer of notebooks.
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Analysis
by VulDB Data Team • 06/11/2021
The vulnerability identified as CVE-2021-22220 represents a critical stored cross-site scripting flaw within GitLab's notebook blob viewer functionality. This security weakness affects all GitLab versions from 13.10 onwards, creating a persistent threat vector that can compromise user sessions and execute malicious code within the context of the victim's browser. The vulnerability specifically resides in how GitLab processes and renders notebook content, particularly when displaying blob data through the notebook viewer interface.
The technical implementation of this flaw stems from insufficient input validation and output encoding within GitLab's notebook rendering engine. When users create or modify notebooks containing malicious script payloads within blob data, the system fails to properly sanitize these inputs before rendering them in the browser. This allows attackers to inject malicious javascript code that persists in the notebook's blob viewer, executing whenever authorized users access the affected content. The vulnerability operates as a stored XSS because the malicious payload is saved server-side and executed against subsequent users who view the compromised notebook.
From an operational perspective, this vulnerability presents significant risks to GitLab organizations as it enables attackers to perform session hijacking, steal sensitive data, and potentially escalate privileges within the GitLab environment. The impact extends beyond individual user compromise to affect entire development teams who may unknowingly access compromised notebooks. Attackers can leverage this vulnerability to execute commands on behalf of authenticated users, potentially leading to unauthorized code commits, repository modifications, or access to confidential project information. The stored nature of the vulnerability means that the malicious code remains active until manually removed from the notebook content.
The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and maps to ATT&CK technique T1566.001 for initial access through malicious content. Organizations should immediately apply the patched versions released by GitLab to address this vulnerability. Mitigation strategies include implementing strict input validation for notebook content, enabling content security policies, and conducting regular security audits of notebook repositories. Additionally, administrators should consider implementing web application firewalls and monitoring for suspicious notebook content modifications to detect potential exploitation attempts. The vulnerability underscores the importance of proper input sanitization and output encoding in web applications, particularly in collaborative environments where users can create and modify content that others will view.