CVE-2026-57289 Overview
CVE-2026-57289 affects the Jenkins Bitbucket Push and Pull Request Plugin version 3.3.8 and earlier. The plugin unconditionally disables SSL/TLS certificate and hostname validation when sending Bearer token authenticated requests to the configured Bitbucket Server endpoint. An attacker positioned to intercept network traffic between Jenkins and the Bitbucket Server can capture the Bearer token and reuse it to access protected repositories or trigger pipeline actions. The flaw is classified under CWE-295: Improper Certificate Validation.
Critical Impact
A network-positioned attacker can intercept Bearer tokens used by Jenkins to authenticate to Bitbucket Server, gaining unauthorized access to source code repositories and CI/CD operations.
Affected Products
- Jenkins Bitbucket Push and Pull Request Plugin 3.3.8 and earlier
- Jenkins controllers configured to integrate with Bitbucket Server via Bearer token authentication
- CI/CD pipelines depending on the affected plugin for webhook and repository operations
Discovery Timeline
- 2026-06-24 - Jenkins publishes Security Advisory SECURITY-3856
- 2026-06-24 - CVE-2026-57289 published to NVD
- 2026-06-25 - Last updated in NVD database
Technical Details for CVE-2026-57289
Vulnerability Analysis
The Bitbucket Push and Pull Request Plugin establishes HTTPS connections to a configured Bitbucket Server endpoint to read repository metadata, post status updates, and handle webhook payloads. When the plugin uses Bearer token authentication, it installs a permissive TrustManager and hostname verifier that accepts any presented certificate. This behavior is unconditional and applies to every Bearer-authenticated request, not just requests against self-signed test environments.
Because certificate and hostname validation are both disabled, the Transport Layer Security (TLS) handshake no longer authenticates the remote endpoint. An adversary with the ability to intercept traffic — through Address Resolution Protocol (ARP) poisoning, rogue Wi-Fi, compromised network infrastructure, or DNS manipulation — can present an arbitrary certificate and decrypt the session.
Root Cause
The root cause is improper certificate validation in the HTTP client used by the plugin for Bearer token flows. The code installs an X509TrustManager that bypasses chain validation and a hostname verifier that returns true for every host, eliminating both authentication checks that TLS provides.
Attack Vector
Exploitation requires a man-in-the-middle (MITM) position on the network path between the Jenkins controller and the Bitbucket Server. The attacker terminates the TLS session, captures the Authorization: Bearer <token> header, and then replays the token to act on behalf of the Jenkins integration. With the captured token, the attacker can read source code, alter pipeline triggers, or post malicious commit statuses. See the Jenkins Security Advisory SECURITY-3856 for vendor details.
Detection Methods for CVE-2026-57289
Indicators of Compromise
- Unexpected outbound TLS connections from the Jenkins controller terminating at hosts other than the configured Bitbucket Server
- Bitbucket Server audit logs showing API activity from the Jenkins service account at unusual times or from unexpected source addresses
- Certificate fingerprints presented to Jenkins that do not match the legitimate Bitbucket Server certificate
- New or modified webhook configurations, branch permissions, or build triggers not initiated by an administrator
Detection Strategies
- Inspect the Jenkins controller's egress traffic and compare observed TLS server certificates against the known Bitbucket Server certificate fingerprint
- Review Bitbucket Server access logs for Bearer token use from IP addresses that do not belong to the Jenkins controller
- Enumerate installed Jenkins plugins and flag any instance running Bitbucket Push and Pull Request Plugin 3.3.8 or earlier
Monitoring Recommendations
- Alert on ARP table changes, unexpected gateway advertisements, and DNS responses on the network segment hosting the Jenkins controller
- Forward Jenkins and Bitbucket Server logs to a centralized Security Information and Event Management (SIEM) platform and correlate authentication events with controller activity
- Track plugin inventory changes across Jenkins controllers so vulnerable versions are surfaced immediately after installation
How to Mitigate CVE-2026-57289
Immediate Actions Required
- Upgrade the Bitbucket Push and Pull Request Plugin to a fixed release as indicated in Jenkins Security Advisory SECURITY-3856
- Rotate any Bearer tokens used by the plugin to authenticate to Bitbucket Server, since previously issued tokens may have been captured
- Restrict the Bitbucket Server token's scope and lifetime to limit the value of any token that was exposed
Patch Information
Apply the plugin update referenced in the Jenkins Security Advisory SECURITY-3856. After updating, restart the Jenkins controller and verify the plugin version on the Manage Plugins page. Confirm that TLS connections to Bitbucket Server now validate the server certificate by intentionally pointing the integration at a host with an invalid certificate — the connection should fail.
Workarounds
- Place the Jenkins controller and Bitbucket Server on a segmented, trusted network so MITM positioning is not feasible until the patch is applied
- Switch the plugin's authentication method to a credential type not affected by the disabled validation if operationally acceptable
- Disable the affected plugin until upgrade is possible, and pause pipelines that rely on Bitbucket Server webhooks
Defenders can complement these steps with endpoint and identity telemetry from platforms such as Singularity Endpoint and Singularity Identity to identify credential reuse and anomalous service account behavior originating from CI/CD infrastructure.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
