CVE-2020-2136 in Git Plugin
Summary
by MITRE
Jenkins Git Plugin 4.2.0 and earlier does not escape the error message for the repository URL for Microsoft TFS field form validation, resulting in a stored cross-site scripting vulnerability.
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Analysis
by VulDB Data Team • 03/10/2020
The vulnerability identified as CVE-2020-2136 resides within the Jenkins Git Plugin version 4.2.0 and earlier, representing a critical security flaw that enables stored cross-site scripting attacks through improper input sanitization. This vulnerability specifically targets the Microsoft TFS field form validation mechanism where error messages containing repository URLs are not properly escaped before being rendered in web interfaces. The flaw creates an environment where malicious actors can inject malicious scripts into the system through carefully crafted repository URL inputs that trigger validation errors, thereby establishing a persistent XSS vector.
The technical implementation of this vulnerability stems from inadequate output encoding practices within the plugin's error handling routines. When Jenkins processes Microsoft TFS repository URLs and encounters validation failures, the system stores error messages containing the problematic URL input directly into its user interface without proper HTML entity encoding or sanitization. This allows attackers to inject malicious JavaScript code that executes within the context of other users' browsers when they view the error messages. The vulnerability operates under CWE-79 which classifies the weakness as "Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')", specifically manifesting as a stored XSS variant where malicious payloads are permanently stored within the application's data stores.
The operational impact of this vulnerability extends beyond simple script execution, as it provides attackers with potential access to sensitive user sessions and administrative privileges within the Jenkins environment. An attacker could craft repository URLs containing malicious payloads that, when validated and stored, would execute whenever legitimate users attempt to view the error messages or interact with the affected fields. This stored nature of the vulnerability means that the malicious code persists even after the initial injection, potentially compromising multiple users over time. The attack vector aligns with ATT&CK technique T1566.001 which describes "Phishing: Spearphishing Attachment" where malicious code is delivered through seemingly legitimate system error messages.
Mitigation strategies for CVE-2020-2136 require immediate patching of the Jenkins Git Plugin to version 4.2.1 or later, which implements proper input sanitization and output encoding for error messages containing repository URLs. Organizations should also implement comprehensive input validation at multiple layers including web application firewalls, regular security scanning of Jenkins instances, and implementation of Content Security Policies to limit script execution capabilities. Additionally, security teams should conduct thorough audits of all Jenkins plugins to identify similar output encoding vulnerabilities and establish mandatory security review processes for plugin updates and installations. Network segmentation and privilege separation should be maintained to limit potential lateral movement if exploitation occurs, while regular security training for administrators can help prevent social engineering attacks that might leverage this vulnerability.