CVE-2026-57304: Jenkins Assembla Auth Bypass Vulnerability

CVE-2026-57304 Overview

CVE-2026-57304 is a missing permission check in the Jenkins Assembla Plugin version 1.4 and earlier. The flaw allows authenticated attackers with Overall/Read permission to instruct the Jenkins controller to initiate connections to an attacker-specified URL using attacker-supplied credentials. The vulnerability maps to CWE-862: Missing Authorization and was disclosed in the Jenkins Security Advisory 2026-06-24. Exploitation enables credential probing, internal service enumeration, and limited server-side request forgery (SSRF) behavior against the Jenkins controller's network position.

Critical Impact
Authenticated users with minimal Overall/Read permission can pivot the Jenkins controller to connect to arbitrary URLs with attacker-supplied credentials, enabling credential validation attacks and internal network probing.

Affected Products

Jenkins Assembla Plugin 1.4
Jenkins Assembla Plugin versions prior to 1.4
Jenkins controllers with the Assembla Plugin installed and enabled

Discovery Timeline

2026-06-24 - Jenkins publishes security advisory SECURITY-3692
2026-06-24 - CVE-2026-57304 published to NVD
2026-06-25 - Last updated in NVD database

Technical Details for CVE-2026-57304

Vulnerability Analysis

The Jenkins Assembla Plugin exposes an HTTP endpoint that establishes outbound connections to a user-supplied URL using a user-supplied username and password. The endpoint does not verify that the calling user holds the appropriate administrative permission before performing this action. Any authenticated user with Overall/Read, which is the default permission required to view the Jenkins UI, can invoke the endpoint.

The vulnerability has two practical exploitation paths. First, an attacker can point the Jenkins controller at an internal URL the attacker cannot otherwise reach, observing response codes and timing to enumerate internal services. Second, the attacker can supply captured credentials to validate them against arbitrary services without triggering authentication logs on the originating host. The plugin functions as a credential oracle and an SSRF primitive bounded by the controller's network reachability.

Root Cause

The root cause is a missing permission check on a plugin form-validation or connection-test method. Jenkins plugin endpoints that perform privileged operations are expected to gate access with a checkPermission call against Jenkins.ADMINISTER or an equivalent scoped permission. The Assembla Plugin omits this check, defaulting access to the broad Overall/Read scope.

Attack Vector

Exploitation requires network access to the Jenkins web interface and a valid account with Overall/Read. The attacker issues an HTTP request to the vulnerable plugin endpoint, supplying a target URL and credential pair. The Jenkins controller performs the outbound connection from its own network context and returns connection status to the attacker.

No verified public proof-of-concept is currently available. Refer to the Jenkins Security Advisory 2026-06-24 for vendor-confirmed technical details.

Detection Methods for CVE-2026-57304

Indicators of Compromise

Outbound HTTP or HTTPS connections originating from the Jenkins controller to unexpected external or internal hosts.
Access log entries showing requests to Assembla Plugin form-validation endpoints by non-administrative user accounts.
Repeated connection attempts from the Jenkins controller to internal IP ranges that do not correspond to known build infrastructure.

Detection Strategies

Audit Jenkins access logs for requests to /descriptorByName/ paths associated with the Assembla Plugin, correlated with the requesting user's permission level.
Monitor outbound network flows from the Jenkins controller and alert on connections to hosts not present in an approved build-system allowlist.
Review the installed plugin inventory for assembla version 1.4 or earlier across all Jenkins instances.

Monitoring Recommendations

Forward Jenkins access.log and audit.log to a centralized logging platform with retention sufficient for incident review.
Establish a network egress baseline for Jenkins controllers and alert on deviations such as connections to non-Assembla hosts.
Track Jenkins user activity using the Audit Trail Plugin to attribute plugin endpoint invocations to specific accounts.

How to Mitigate CVE-2026-57304

Immediate Actions Required

Identify all Jenkins instances running the Assembla Plugin and inventory their versions.
Restrict the Overall/Read permission to trusted users until a patched version is deployed.
Disable or uninstall the Assembla Plugin if Assembla integration is not actively used.
Rotate any credentials that may have been supplied to the plugin during testing or exploitation windows.

Patch Information

At the time of disclosure, no fixed version was announced in the Jenkins Security Advisory 2026-06-24. Administrators should monitor the advisory page for an updated release of the Assembla Plugin and apply it when published.

Workarounds

Remove the Assembla Plugin from Jenkins controllers where the integration is not required.
Apply network egress controls on Jenkins controllers to restrict outbound connections to an explicit allowlist.
Enforce matrix-based or project-based authorization and limit Overall/Read to a narrow set of authenticated users.

bash

# List installed Jenkins plugins and check Assembla version via Jenkins CLI
java -jar jenkins-cli.jar -s https://jenkins.example.com/ \
  -auth admin:API_TOKEN \
  list-plugins | grep -i assembla

# Uninstall the plugin if Assembla integration is not required
java -jar jenkins-cli.jar -s https://jenkins.example.com/ \
  -auth admin:API_TOKEN \
  disable-plugin assembla -restart