CVE-2026-87785: Apache Syncope Auth Bypass Vulnerability

CVE-2026-87785 Overview

CVE-2026-87785 is an authentication bypass by spoofing vulnerability in Apache Syncope, an open-source identity management system. The flaw exists in the internal JSON Web Token (JWT) authentication mechanism. When the configured JSON Web Key Set (JWKS) settings, including protocol and key material, are disclosed, an authenticated attacker can forge a JWT that impersonates another user. The attacker gains the privileges of the spoofed identity after presenting a valid but crafted token. The vulnerability is classified under [CWE-290: Authentication Bypass by Spoofing].

Critical Impact
An authenticated attacker who obtains JWKS configuration details can spoof arbitrary users, including administrators, leading to full compromise of Syncope-managed identities and downstream provisioned systems.

Affected Products

Apache Syncope 3.0.0-M0 through 3.0.16
Apache Syncope 4.0.0-M0 through 4.0.7
Apache Syncope 4.1.0-M0 through 4.1.2

Discovery Timeline

2026-09-14 - CVE-2026-87785 published to the National Vulnerability Database (NVD)
2026-09-14 - Apache Syncope project publishes advisory via the Apache Mailing List Thread and Openwall OSS-Security Discussion
2026-09-14 - Last updated in NVD database

Technical Details for CVE-2026-87785

Vulnerability Analysis

Apache Syncope uses internal JWTs to authenticate service-to-service and administrative requests. The tokens are signed and validated against a JWKS configuration that defines the signing protocol and key material. When those JWKS parameters are exposed, an attacker who has already authenticated with valid low-privilege credentials can generate a new JWT that asserts a different user identity. The Syncope authentication layer accepts the forged token because it validates against the same disclosed key, granting the attacker the privileges of the spoofed principal. The attack requires network reachability to the Syncope API and no user interaction.

Root Cause

The root cause is insufficient separation between JWKS configuration disclosure and JWT trust validation. Syncope trusts any token that verifies against the configured key without binding it to session context or the originally authenticated subject. Disclosure of the protocol and key removes the only barrier preventing token forgery.

Attack Vector

An attacker completes a legitimate authentication flow to obtain a valid JWT and observes or otherwise obtains the JWKS settings. The attacker then constructs a new JWT with modified claims that assert a target user, signs it with the disclosed key, and submits the token to a Syncope endpoint. Syncope validates the signature, accepts the impersonated identity, and grants the associated privileges.

No verified public exploit code is available for CVE-2026-87785. Refer to the Apache Mailing List Thread for technical detail from the maintainers.

Detection Methods for CVE-2026-87785

Indicators of Compromise

Successful authentications where the JWT sub claim does not match the user recorded in prior session or login events.
Sudden privilege escalations for accounts that did not receive role changes through normal provisioning workflows.
API requests using JWTs issued outside the expected token issuance windows or from unexpected source addresses.

Detection Strategies

Correlate Syncope audit logs with authentication logs to identify JWTs whose claimed subject differs from the authenticating principal.
Alert on administrative operations executed by accounts that have no historical baseline of administrative activity.
Inspect access logs for repeated requests to /syncope/rest/ endpoints using distinct JWTs from the same source in short intervals.

Monitoring Recommendations

Enable verbose audit logging on Apache Syncope core, console, and enduser modules and forward events to a central analytics platform.
Monitor egress and configuration endpoints that could disclose JWKS material, including reverse proxy and management interfaces.
Track privileged role assignments and out-of-band changes to Syncope user entitlements.

How to Mitigate CVE-2026-87785

Immediate Actions Required

Upgrade Apache Syncope to version 4.0.8 or 4.1.3, which contain the fix. Version 3.0.x has not received a fix in the referenced advisory, so plan migration.
Rotate all JWKS signing keys after the upgrade to invalidate any tokens forged with previously disclosed material.
Review Syncope audit logs for anomalous authentications and revoke sessions for any suspicious activity.

Patch Information

The Apache Syncope project has released fixed versions 4.0.8 and 4.1.3. Both releases address the JWT validation weakness that allows spoofing when JWKS parameters are known. Deployments on the 3.0.x branch must upgrade to a supported 4.x release to receive the fix. Full release details are available in the Apache Mailing List Thread.

Workarounds

Restrict network access to Syncope administrative and API endpoints so that only trusted management networks can reach them.
Protect JWKS configuration data from disclosure by restricting file system, configuration store, and admin console access.
Force reissuance of internal signing keys and shorten JWT lifetimes to reduce the window in which forged tokens are accepted.

bash

# Configuration example
# Upgrade Apache Syncope using Maven (adjust to your build system)
mvn versions:set -DnewVersion=4.1.3
mvn clean install

# After upgrade, rotate the JWKS signing key referenced in core.properties
# jwt.key=<new-strong-random-key>