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CVE-2026-42797 exposes a flaw in Apache Syncope where an administrator with privileges to define Derived Schemas can inject a malicious JEXL (Java Expression Language) expression. Syncope uses JEXL to compute derived attribute values based on user data. Normally, these expressions are sandboxed, but this version range lacks sufficient restrictions. An attacker who already has “Derived Schemas” create/edit rights can craft a JEXL expression that, when evaluated during user read operations, accesses internal objects or methods. The expression can traverse object graphs to retrieve security-sensitive fields such as passwords, security answers, or token hashes—fields normally hidden from standard user views. When another administrator with “User read” permissions views a user, the malicious JEXL executes in the context of the read operation, returning extra data embedded in derived attributes. The issue stems from improper filtering of JEXL’s introspection capabilities, allowing calls like `user.getPassword()` or user.getSecurityQuestion().getAnswer(). This bypasses intended access controls because the derived attribute’s result is presented as legitimate schema output. Attackers need no additional privileges beyond what they already possess; the combination of two roles (Derived Schemas admin + User read) triggers the leak. The vulnerability affects all Syncope versions from 3.0 to 3.0.16, 4.0 to 4.0.5, and 4.1.0. Upgrading to 4.0.6 or 4.1.1 resolves it by limiting JEXL context to a whitelist of safe methods and rejecting dangerous property navigation.
DailyCVE Form:
Platform: Apache Syncope
Version: 3.0-3.0.16,4.0-4.0.5,4.1.0
Vulnerability: JEXL expression injection
Severity: Medium
date: 2026-05-25
Prediction: 2026-06-10
What Undercode Say:
Identify vulnerable endpoints via Syncope console
curl -u admin:password "https://syncope.example.com/syncope/rest/users?details=all" | jq '.result[].derivedSchema'
Check installed version
curl -s "https://syncope.example.com/syncope/rest/status/version" | grep -E "3.[0-9]+.[0-9]+|4.[0-1].[0-9]+"
Malicious JEXL test (requires Derived Schemas create)
curl -X POST -u admin:password "https://syncope.example.com/syncope/rest/schemas/derived" -H "Content-Type: application/json" -d '{"key":"evil","expression":"user.password","jexlEngine":"commons-jexl3"}'
Read user to trigger leak
curl -u admin:password "https://syncope.example.com/syncope/rest/users/username/admin?details=derived" | grep -A5 "evil"
Exploit:
- Create Derived Schema with expression: `user.securityQuestion.answer`
– Assign schema to user view - Read any user → answer field exposed
Protection:
- Upgrade to Syncope 4.0.6 or 4.1.1
- Restrict JEXL to whitelist: `org.apache.syncope.core.provisioning.api.jexl.JexlUtils.safeMethods`
– Remove Derived Schemas privilege from untrusted admins
Impact:
- Leak hashed passwords, security answers, OAuth tokens, and MFA secrets
- Lateral movement to admin accounts
- Compliance breach (GDPR, HIPAA) for sensitive user data exposure
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Sources:
Reported By: nvd.nist.gov
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