CVE-2021-21602 in Jenkins
Summary
by MITRE • 01/14/2021
Jenkins 2.274 and earlier, LTS 2.263.1 and earlier allows reading arbitrary files using the file browser for workspaces and archived artifacts by following symlinks.
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Analysis
by VulDB Data Team • 02/14/2021
This vulnerability exists in Jenkins versions up to 2.274 and LTS versions up to 2.263.1 where the file browser functionality for workspaces and archived artifacts fails to properly validate symbolic link paths. The flaw allows authenticated users to traverse filesystem boundaries and access arbitrary files on the Jenkins server through carefully crafted symlinked paths. This represents a classic path traversal vulnerability that leverages the insufficient input sanitization of symbolic link references within the file browsing interface. The vulnerability is categorized under CWE-22 Path Traversal and aligns with ATT&CK technique T1059.007 Command and Scripting Interpreter: PowerShell, as it enables unauthorized file access that could lead to further exploitation. The issue stems from the lack of proper path normalization and validation when resolving symbolic links in the workspace and archived artifacts browsing functionality. Attackers can exploit this by creating malicious symlinks that point to sensitive files such as configuration files, credential stores, or system binaries, effectively bypassing normal access controls. The impact extends beyond simple information disclosure as it can potentially lead to privilege escalation or lateral movement within the affected environment.
The operational impact of this vulnerability is significant for organizations relying on Jenkins for continuous integration and deployment workflows. Attackers with minimal privileges can access sensitive artifacts including build scripts, environment variables, and potentially even source code repositories that are stored within the Jenkins workspace. This vulnerability particularly affects environments where Jenkins serves as a central build and deployment system, as it could expose critical infrastructure components and secrets that are typically protected by proper access controls. The vulnerability can be exploited through the web interface without requiring special privileges beyond basic Jenkins user access, making it particularly dangerous in multi-tenant environments where different projects might share the same Jenkins instance. Organizations with tight security requirements and compliance mandates face increased risk as this vulnerability could potentially violate security policies around data protection and access control. The exploitability of this vulnerability is enhanced by the fact that it requires no special tools or techniques beyond standard Jenkins user interaction, making it accessible to attackers with basic knowledge of the system.
Mitigation strategies should focus on immediate patching of affected Jenkins versions to the latest releases that contain the necessary security fixes. Organizations should also implement additional access controls and privilege separation to minimize the impact of potential exploitation. The recommended approach includes disabling the file browser functionality for workspaces and archived artifacts if it is not essential for operations, or implementing proper symlink validation and path normalization at the application level. Security teams should conduct comprehensive audits of Jenkins configurations to identify and remove any unnecessary symbolic links that could be exploited. Network segmentation and firewall rules should be implemented to restrict direct access to Jenkins servers where possible. The implementation of automated monitoring and alerting for unusual file access patterns can help detect potential exploitation attempts. Organizations should also review their Jenkins security configurations and ensure that proper authentication and authorization controls are in place. Regular security assessments and penetration testing should be conducted to identify similar vulnerabilities in the Jenkins ecosystem and other CI/CD tools. The vulnerability highlights the importance of proper input validation and access control mechanisms in web applications, particularly those handling file system operations and user-provided paths.