CVE-2026-57305: Jenkins Assembla Plugin CSRF Vulnerability Analysis

Technical summary

CVE-2026-57305 is a CSRF vulnerability (CWE-352) in the Jenkins Assembla Plugin affecting version 1.4 and earlier. The vulnerability stems from insufficient protection against cross-site request forgery in the plugin's connection handling. An authenticated attacker can craft a malicious request that, when clicked by a Jenkins administrator, causes the plugin to establish a connection to an attacker-specified URL using attacker-provided username and password credentials. The attack requires an authenticated user (PR:L) and no user interaction from the victim beyond visiting a malicious page, though the impact is limited to partial confidentiality and integrity compromise without affecting availability.

Business impact

If exploited, this vulnerability could allow attackers to redirect Jenkins Assembla Plugin connections to malicious servers, potentially compromising credentials, intercepting sensitive data, or poisoning CI/CD pipeline integrations. Organizations relying on this plugin for build automation or deployment workflows may face unauthorized access to connected systems, data breaches, or pipeline integrity violations. The risk is heightened in multi-tenant Jenkins environments where administrative accounts have broad permissions.

Affected systems

The vulnerability affects Jenkins Assembla Plugin version 1.4 and all earlier versions. Jenkins instances with this plugin installed and configured are at risk, particularly those exposed to authenticated users with access to plugin configuration pages. The vulnerability does not affect other Jenkins plugins or the core Jenkins platform itself.

Exploitability

Exploitation requires an authenticated attacker with Jenkins access and the ability to trick an administrator into clicking a malicious link or visiting a malicious page. The attack vector is network-based with low complexity, making it practical for insiders or attackers who have gained initial Jenkins access. However, the requirement for prior authentication and admin interaction limits the severity and scope of real-world exploitation.

Remediation

Organizations should upgrade the Jenkins Assembla Plugin to a version newer than 1.4 that includes CSRF protections. If an upgrade is not immediately available, restrict access to the plugin's configuration pages to trusted administrators only, and implement network segmentation to limit outbound connections from Jenkins to known, trusted endpoints. Consider disabling the plugin if it is not actively used.

Patch guidance

Check the Jenkins plugin marketplace and the Assembla Plugin project repository for a patched version addressing CVE-2026-57305. Apply patches as soon as they become available. Verify the patch version against official Jenkins and plugin vendor advisories before deployment. Test patches in a non-production environment first to ensure compatibility with your Jenkins configuration and other installed plugins.

Detection guidance

Monitor Jenkins logs for unusual outbound connections initiated by the Assembla Plugin, especially to unfamiliar or non-whitelisted domains. Review Jenkins audit logs for unexpected changes to plugin configuration settings, particularly modifications to connection URLs or credentials. Network-based detection should flag outbound connections from Jenkins to suspicious external endpoints. Consider implementing web application firewalls to detect CSRF attack patterns targeting Jenkins administrative interfaces.

Why prioritize this

While the CVSS score of 5.4 (MEDIUM) reflects limited scope and the requirement for prior authentication, the plugin's role in connecting Jenkins to external systems elevates practical risk. Any compromise of plugin credentials or connections could cascade into broader CI/CD pipeline compromise. Organizations using this plugin should prioritize patching before the next maintenance window, especially if the plugin is actively used for production deployments.

Risk score, explained

The CVSS 3.1 score of 5.4 reflects a network-based attack with low complexity, low privilege requirements, and no special user interaction needed from the perspective of the attacker controlling the malicious request. However, practical exploitation still requires an authenticated user and some social engineering. The score correctly assigns low impact to confidentiality and integrity (partial information disclosure and configuration tampering) while noting no availability impact. The MEDIUM severity appropriately captures that while the vulnerability is real and exploitable, its scope is limited by authentication requirements and the specific plugin context.

Frequently asked questions