CVE-2018-19573 in Community Edition
Summary
by MITRE
GitLab CE/EE, versions 10.3 up to 11.x before 11.3.11, 11.4 before 11.4.8, and 11.5 before 11.5.1, are vulnerable to an XSS vulnerability in Markdown fields via Mermaid.
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Analysis
by VulDB Data Team • 06/23/2024
This vulnerability exists in GitLab Community Edition and Enterprise Edition versions within specific ranges, representing a cross-site scripting flaw that can be exploited through Markdown fields utilizing Mermaid diagram rendering capabilities. The issue affects versions from 10.3 up to 11.x before 11.3.11, 11.4 before 11.4.8, and 11.5 before 11.5.1, making it a significant security concern for organizations relying on GitLab for code repository management and collaboration. The vulnerability specifically manifests when users input malicious content into Markdown fields that support Mermaid diagram generation, creating an attack vector that could compromise user sessions and potentially lead to unauthorized access to sensitive repository data.
The technical flaw stems from insufficient input validation and sanitization within GitLab's Markdown processing pipeline, particularly when handling Mermaid diagram syntax. When users create or edit Markdown content containing Mermaid diagrams, the system fails to properly sanitize user-supplied input before rendering these diagrams, allowing malicious JavaScript code embedded within the Mermaid syntax to execute in the context of other users' browsers. This occurs because the Mermaid rendering engine does not adequately filter or escape special characters that could be interpreted as executable code, enabling attackers to inject malicious scripts that persist in the repository and execute whenever other users view the affected content. The vulnerability aligns with CWE-79 which specifically addresses Cross-Site Scripting flaws in web applications, and represents a classic case of insufficient output escaping in dynamic content generation.
The operational impact of this vulnerability extends beyond simple script execution, potentially enabling attackers to hijack user sessions, steal sensitive information, or perform unauthorized actions within the GitLab environment. An attacker could craft malicious Mermaid diagrams containing JavaScript payloads that would execute when other users view the repository content, leading to session hijacking, data exfiltration, or privilege escalation within the GitLab instance. The vulnerability affects all users who have access to repositories where such content can be submitted, making it particularly dangerous in collaborative environments where multiple developers contribute to shared projects. This XSS vulnerability could be exploited to gain persistent access to repositories, manipulate code reviews, or even escalate privileges to administrative levels within the GitLab instance, depending on the specific configuration and access controls in place.
Organizations should immediately apply the vendor patches released for versions 11.3.11, 11.4.8, and 11.5.1 to remediate this vulnerability, as these releases contain the necessary input sanitization and output escaping mechanisms to prevent malicious code execution. System administrators should also implement additional monitoring for suspicious Markdown content submissions and consider implementing Content Security Policy headers to limit the execution of inline scripts within GitLab environments. The mitigation strategy should include regular security assessments of user-generated content processing capabilities and enhanced input validation for all dynamic content rendering features. Organizations using older versions of GitLab should prioritize upgrading to supported releases that include proper sanitization of Mermaid and other diagram rendering features, as these vulnerabilities often serve as initial access points for more sophisticated attacks within development environments. This vulnerability demonstrates the importance of comprehensive input validation across all user-facing features, particularly those involving dynamic content generation and rendering capabilities that are common in modern collaborative development platforms.