CVE-2026-84668: Jenkins SAML Plugin Auth Bypass Vulnerability

CVE-2026-84668 Overview

CVE-2026-84668 affects the Jenkins SAML Plugin version 4.618.v441a_27fa_46d2 and earlier. The vulnerability allows an authenticated attacker to overwrite the Security Assertion Markup Language (SAML) identity provider metadata file through Stapler data binding. An attacker with low-privilege access can replace the metadata file with attacker-controlled content. This substitution enables authentication as any user, including administrators, resulting in full compromise of the Jenkins instance.

Critical Impact
Attackers with low-privileged Jenkins accounts can replace SAML identity provider metadata and authenticate as arbitrary users, including administrators.

Affected Products

Jenkins SAML Plugin version 4.618.v441a_27fa_46d2 and earlier
Jenkins controllers configured with SAML-based single sign-on
Downstream Jenkins deployments relying on the affected plugin for identity federation

Discovery Timeline

2026-09-02 - Jenkins Security Advisory published as SECURITY-4065
2026-09-02 - CVE-2026-84668 published to NVD
2026-09-02 - Last updated in NVD database

Technical Details for CVE-2026-84668

Vulnerability Analysis

The Jenkins SAML Plugin manages identity provider (IdP) metadata used to validate SAML assertions during single sign-on. The plugin exposes configuration properties that Stapler, the Jenkins web framework, binds directly from HTTP request parameters. This binding path reaches the file that stores the on-disk IdP metadata without adequate authorization enforcement. An authenticated attacker sends a crafted request that writes arbitrary content to the metadata file. Because Jenkins trusts this file as the authoritative IdP definition, subsequent SAML assertions signed by an attacker-controlled key are accepted as valid. The flaw is classified under [CWE-284: Improper Access Control].

Root Cause

The root cause is missing permission checks on a Stapler-exposed setter that persists SAML IdP metadata. Stapler automatically maps request parameters to Java setter methods, and the plugin does not gate this path with an administrative permission check. Any authenticated user reaching the endpoint can overwrite the metadata file.

Attack Vector

The attack requires network access to the Jenkins web interface and a valid low-privileged account. The attacker submits a crafted HTTP request that triggers Stapler data binding on the vulnerable property, writing attacker-controlled XML into the IdP metadata file. The attacker then initiates a SAML login and presents an assertion signed by their own key, which the plugin now trusts. The plugin authenticates the session as the impersonated principal, including administrator accounts. See the Jenkins Security Advisory 2026-09-02 for technical details.

No verified proof-of-concept code is publicly available at time of writing.

Detection Methods for CVE-2026-84668

Indicators of Compromise

Unexpected modifications to the SAML IdP metadata file on the Jenkins controller filesystem
Successful SAML authentications for administrative accounts from unusual source IP addresses or user agents
New or unrecognized signing certificates or entity IDs present in the plugin configuration
Jenkins audit log entries showing configuration changes to the SAML plugin from non-administrator users

Detection Strategies

Monitor file integrity on the Jenkins home directory, specifically the SAML plugin metadata file, and alert on writes outside change windows
Correlate HTTP access logs for POST requests targeting SAML plugin configuration endpoints originating from non-administrative sessions
Baseline expected SAML IdP entity IDs and certificate fingerprints, then alert on deviations observed in authentication events

Monitoring Recommendations

Ingest Jenkins system, audit, and access logs into a centralized SIEM with retention sufficient to reconstruct authentication chains
Track privilege escalations and first-time administrator logins across all Jenkins controllers
Alert on successful logins that occur within a short window after configuration changes to authentication plugins

How to Mitigate CVE-2026-84668

Immediate Actions Required

Upgrade the Jenkins SAML Plugin to the fixed version released in Jenkins Security Advisory 2026-09-02
Audit the SAML IdP metadata file for unauthorized modifications and restore from a known-good backup if tampering is suspected
Rotate administrator credentials and review recent SAML authentication events for signs of impersonation
Restrict Jenkins account creation and enforce least privilege for all authenticated users

Patch Information

Jenkins has released a fixed version of the SAML Plugin. Refer to the Jenkins Security Advisory 2026-09-02 for exact fixed version numbers and upgrade instructions. Apply the update through the Jenkins Update Center or by replacing the plugin .hpi artifact on the controller.

Workarounds

Temporarily disable the SAML Plugin and fall back to a hardened authentication realm until the patched version is deployed
Restrict network access to the Jenkins web interface to trusted administrative networks using a reverse proxy or firewall
Disable self-service account signup and remove unnecessary authenticated user accounts to reduce the pool of potential attackers

bash

# Verify installed Jenkins SAML Plugin version via the Jenkins CLI
java -jar jenkins-cli.jar -s https://jenkins.example.com/ list-plugins | grep saml