CVE-2026-57304: Jenkins Assembla Plugin Missing Permission Check

Technical summary

CVE-2026-57304 is a missing permission check (CWE-862) in Jenkins Assembla Plugin affecting versions 1.4 and earlier. The plugin does not adequately enforce authorization when processing requests to establish connections to external Assembla endpoints. An authenticated attacker holding only Overall/Read permission—a low privilege level in Jenkins—can bypass normal administrative controls and issue connection requests with arbitrary URLs and embedded credentials. The vulnerability is network-accessible and requires only valid Jenkins authentication; no additional interaction or elevated privileges are needed to trigger the flaw.

Business impact

This vulnerability reduces Jenkins' ability to enforce proper separation of duties. Attackers with read-only access gain the ability to create unauthorized connections to third-party systems, bypassing credential management and approval workflows. In environments where Jenkins integrates with version control, artifact repositories, or issue tracking systems, this could enable exfiltration of project metadata, secrets stored in jobs, or manipulation of build artifacts. The risk is amplified if the same credentials are reused across multiple systems.

Affected systems

Jenkins Assembla Plugin versions 1.4 and earlier are affected. This impacts Jenkins instances that have the Assembla Plugin installed and have users with Overall/Read permission (a standard permission level for developers and CI/CD operators). Jenkins on any platform (Linux, Windows, Docker, cloud-hosted) is affected if the vulnerable plugin is active.

Exploitability

Exploitation requires valid Jenkins credentials at the Overall/Read permission level, which is commonly granted to developers. No special authentication bypass is needed; the vulnerability lies in insufficient authorization checks on a standard operation. The attack surface is limited to authenticated users, but the permission threshold is low. Real-world exploitation risk is elevated in multi-tenant or open Jenkins environments where read access is broadly granted.

Remediation

Update Jenkins Assembla Plugin to a version greater than 1.4. Review vendor advisories for patch availability and version recommendations. If an immediate patch is unavailable, restrict Overall/Read permission to trusted users only and disable the Assembla Plugin if not actively in use. Monitor plugin configuration for unexpected external connection attempts.

Patch guidance

Consult the Jenkins Security Advisory and the Assembla Plugin project repository for the latest patched version. Verify against the vendor advisory to confirm the minimum safe version number. Apply patches via the Jenkins plugin manager or manual installation. Test in a non-production environment before rolling out to production instances to ensure no breaking changes to existing Assembla integrations.

Detection guidance

Monitor Jenkins audit logs for connection creation or modification events initiated by users with read-only privileges. Alert on any unexpected outbound connections from Jenkins to unfamiliar external URLs. Review Assembla Plugin configuration via the Jenkins UI for connections with unexpected hostnames or credentials. SIEM integration with Jenkins logs can help identify lateral reconnaissance patterns following a successful exploitation.

Why prioritize this

Although the CVSS score is moderate (5.4), the low permission barrier and straightforward exploitation path warrant timely attention. The ability for read-only users to bypass administrative controls and interact with external systems violates least-privilege principles and could accelerate compromise chains in a broader attack scenario. Organizations with large or untrusted Jenkins user bases should prioritize this higher.

Risk score, explained

The CVSS 3.1 score of 5.4 reflects a medium-severity issue requiring low attack complexity and no user interaction, with limited impact (read and write access to a single external resource). However, the score does not fully capture the policy violation and trust-boundary breakdown; risk should be elevated in environments where Jenkins is a critical deployment or integration hub.

Frequently asked questions