CVE-2020-10693: Hibernate Validator Auth Bypass Flaw

CVE-2020-10693 Overview

A flaw was found in Hibernate Validator version 6.1.2.Final where a bug in the message interpolation processor enables invalid EL (Expression Language) expressions to be evaluated as if they were valid. This vulnerability allows attackers to bypass input sanitation controls (escaping, stripping) that developers may have implemented when handling user-controlled data in error messages.

Critical Impact

Attackers can bypass input validation and sanitization controls in error messages, potentially leading to injection attacks or information disclosure in applications using Hibernate Validator.

Affected Products

• Red Hat Hibernate Validator (versions prior to fix)
• IBM WebSphere Application Server (Liberty)
• Red Hat JBoss Enterprise Application Platform 7.2.0 and 7.3.0
• Red Hat Enterprise Linux 6.0, 7.0, and 8.0
• Red Hat Satellite 6.8
• Red Hat Satellite Capsule 6.8
• Quarkus
• Oracle WebLogic Server 14.1.1.0.0

Discovery Timeline

• May 6, 2020 - CVE-2020-10693 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-10693

Vulnerability Analysis

This vulnerability exists in the message interpolation processor of Hibernate Validator. When validation errors occur, Hibernate Validator interpolates error messages which may include EL expressions. The flaw allows malformed or invalid EL expressions to be processed and evaluated as if they were valid expressions.

This behavior is particularly dangerous when applications incorporate user-controlled input into validation error messages. Developers often implement escaping or stripping controls to prevent EL injection attacks, but this bug allows attackers to craft specially-formed input that bypasses these protective measures.

Root Cause

The root cause lies in improper input validation (CWE-20) within the message interpolation processor. The processor fails to properly validate and reject invalid EL expressions before evaluation, allowing malformed expressions to slip through security controls that would normally block them.

When the validator processes constraint violation messages, it parses EL expressions within the message templates. The bug causes the parser to mishandle certain invalid expression formats, treating them as valid and proceeding with evaluation rather than rejecting them outright.

Attack Vector

The attack is network-based and can be executed remotely without authentication. An attacker can exploit this vulnerability by:

1. Identifying input fields validated by Hibernate Validator where error messages include user input
2. Crafting malformed EL expressions designed to bypass escaping/stripping controls
3. Submitting the crafted input to trigger validation errors
4. The malformed expressions are evaluated during message interpolation, bypassing security controls

The vulnerability does not require user interaction, and the attack complexity is low, making it accessible to a wide range of attackers targeting Java applications using Hibernate Validator for bean validation.

Detection Methods for CVE-2020-10693

Indicators of Compromise

• Unusual validation error messages containing unexpected EL expression syntax
• Application logs showing EL expression evaluation errors with malformed syntax
• Unexpected behavior in validation error handling workflows
• Evidence of attempted EL injection patterns in input fields

Detection Strategies

• Monitor application logs for validation-related errors with EL expression syntax anomalies
• Implement input logging on validation endpoints to detect injection attempts
• Deploy web application firewall rules to detect EL injection patterns
• Review application dependencies to identify vulnerable Hibernate Validator versions

Monitoring Recommendations

• Enable detailed logging for Hibernate Validator message interpolation activities
• Monitor for patterns indicative of EL injection attempts in user-submitted data
• Set up alerts for validation processing anomalies or unexpected expression evaluations
• Regularly audit application dependencies for known vulnerable versions

How to Mitigate CVE-2020-10693

Immediate Actions Required

• Upgrade Hibernate Validator to a patched version that addresses the EL expression bypass
• Review application code for instances where user input is included in validation error messages
• Implement additional server-side validation beyond Hibernate Validator for sensitive inputs
• Apply vendor-specific patches from Red Hat, IBM, or Oracle as applicable to your deployment

Patch Information

Vendors have released security updates addressing this vulnerability. Refer to the Oracle Security Alert for Oracle product patches. For Red Hat products, consult the Red Hat Bug Report for patch availability and remediation guidance. Organizations using IBM WebSphere Application Server Liberty should check IBM's security bulletins for applicable fixes.

Workarounds

• Avoid including user-controlled data directly in validation error messages
• Implement custom message interpolators that strictly validate EL expression syntax before evaluation
• Use parameterized messages instead of string concatenation for error message construction
• Apply input sanitization at multiple layers rather than relying solely on Hibernate Validator escaping