CVE-2026-42797 Overview
CVE-2026-42797 is an information disclosure vulnerability in Apache Syncope, an open-source identity management system. The flaw resides in the Derived Schemas feature, where administrators with sufficient entitlements can craft malicious Java Expression Language (JEXL) expressions. These expressions allow any administrator with User read entitlements to access User-related security-sensitive information that should remain protected. The issue affects Apache Syncope versions 3.0 through 3.0.16, 4.0 through 4.0.5, and 4.1.0. The vulnerability is categorized under [CWE-202]: Exposure of Sensitive Information Through Data Queries.
Critical Impact
Authenticated administrators can abuse JEXL expressions in Derived Schemas to disclose User-related sensitive data, breaking confidentiality controls in identity management deployments.
Affected Products
- Apache Syncope 3.0 through 3.0.16
- Apache Syncope 4.0 through 4.0.5
- Apache Syncope 4.1.0
Discovery Timeline
- 2026-05-25 - CVE-2026-42797 published to NVD
- 2026-05-26 - Last updated in NVD database
Technical Details for CVE-2026-42797
Vulnerability Analysis
Apache Syncope uses Derived Schemas to compute attribute values from other attributes using JEXL expressions. The vulnerability stems from insufficient restrictions on what these JEXL expressions are permitted to evaluate. An administrator who holds entitlements to define Derived Schemas can craft an expression that reaches into User objects and returns security-sensitive data. When another administrator with User read entitlements subsequently reads a User, the malicious JEXL expression executes and surfaces protected information that the reading administrator would not normally be authorized to view. The flaw functions as a privilege boundary violation between administrator roles within Syncope's role-based access control model.
Root Cause
The root cause is overly permissive JEXL expression definitions in Derived Schemas. Syncope did not adequately constrain which object properties and methods a Derived Schema expression could access. JEXL is a powerful expression language, and without explicit allow-listing of safe references, expressions can dereference sensitive fields on the User object graph. The fix in versions 4.0.6 and 4.1.1 further restricts the JEXL expression definition surface available to Derived Schema authors.
Attack Vector
Exploitation requires two authenticated administrators with distinct entitlements. First, an administrator with entitlements over Derived Schemas defines a malicious JEXL expression referencing sensitive User attributes. Second, any administrator with User read entitlements triggers evaluation of the derived attribute during a normal read operation. The result returns sensitive data to the reading administrator. The attack is network-reachable through the standard Syncope administrative API and does not require user interaction beyond the privileged actions described.
No public proof-of-concept code has been released. See the Apache Mailing List Thread and OpenWall OSS Security Discussion for technical details.
Detection Methods for CVE-2026-42797
Indicators of Compromise
- Newly created or modified Derived Schema definitions containing JEXL expressions that reference User security attributes such as password hashes, security questions, or token fields.
- Unexpected administrator activity around the /derivedSchemas REST endpoint, particularly creation or update operations.
- Audit log entries showing Derived Schema changes followed by User read operations from administrator accounts with limited entitlements.
Detection Strategies
- Inventory all existing Derived Schemas and review their JEXL expressions for references to sensitive User fields or method calls that traverse the object graph.
- Correlate Syncope audit logs to identify administrators who both modified Derived Schemas and performed User read operations in close temporal proximity.
- Alert on administrative API calls that create or update Derived Schemas, especially from accounts that do not routinely manage schemas.
Monitoring Recommendations
- Enable verbose audit logging for entitlement-bearing administrator actions, including Derived Schema CRUD operations and User reads.
- Forward Syncope audit logs to a centralized SIEM or data lake for correlation and long-term retention.
- Review administrator entitlement assignments quarterly to ensure separation of duties between schema authors and User readers.
How to Mitigate CVE-2026-42797
Immediate Actions Required
- Upgrade Apache Syncope to version 4.0.6 or 4.1.1, which restrict the JEXL expression definition surface.
- Audit all existing Derived Schema definitions and remove any expression that references sensitive User attributes.
- Reduce the number of administrators holding Derived Schema management entitlements to the minimum required.
Patch Information
The Apache Syncope project released versions 4.0.6 and 4.1.1 to fix CVE-2026-42797 by further restricting allowable JEXL expression definitions in Derived Schemas. Users on the 3.0.x branch should monitor the Apache Syncope announcements for backported guidance. Refer to the Apache Mailing List Thread for the official advisory.
Workarounds
- Restrict Derived Schema management entitlements to a small, trusted set of administrators until upgrades are complete.
- Implement four-eyes review for any new or modified Derived Schema definitions through change-management processes.
- Temporarily disable Derived Schemas that are not business-critical to reduce the attack surface.
# Example: upgrade Apache Syncope using Maven coordinates
# Update pom.xml dependency versions, then rebuild and redeploy
mvn versions:set-property -Dproperty=syncope.version -DnewVersion=4.1.1
mvn clean install
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
