CVE-2025-40758: Mendix SAML Auth Bypass Vulnerability

CVE-2025-40758 Overview

A critical authentication bypass vulnerability has been identified in the Mendix SAML module that affects multiple Mendix platform versions. The vulnerability stems from insufficient enforcement of signature validation and binding checks within the SAML authentication process. This weakness could allow unauthenticated remote attackers to hijack user accounts in specific Single Sign-On (SSO) configurations, potentially leading to complete account takeover without requiring any user interaction.

Critical Impact

Unauthenticated remote attackers can exploit improper SAML signature validation to hijack user accounts in affected SSO configurations, enabling unauthorized access to protected applications and resources.

Affected Products

• Mendix SAML (Mendix 10.12 compatible) - All versions < V4.0.3
• Mendix SAML (Mendix 10.21 compatible) - All versions < V4.1.2
• Mendix SAML (Mendix 9.24 compatible) - All versions < V3.6.21

Discovery Timeline

• 2025-08-14 - CVE-2025-40758 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-40758

Vulnerability Analysis

This vulnerability is classified under CWE-347 (Improper Verification of Cryptographic Signature), which occurs when software fails to properly verify that data has been signed by a specific entity. In the context of SAML authentication, signature validation is a critical security control that ensures SAML assertions originate from a trusted Identity Provider (IdP) and have not been tampered with during transit.

The Mendix SAML module's insufficient enforcement of signature validation and binding checks creates an exploitable condition where attackers can craft malicious SAML responses or assertions that bypass authentication controls. This type of vulnerability is particularly severe in enterprise SSO environments where SAML serves as the trust boundary between identity providers and service providers.

The network-based attack vector means that exploitation can occur remotely without requiring local access to the target system. While the attack complexity is high due to the specific SSO configurations required, successful exploitation requires no privileges or user interaction, making it a significant concern for organizations using affected Mendix SAML configurations.

Root Cause

The root cause of CVE-2025-40758 lies in the improper verification of cryptographic signatures within the Mendix SAML module. Specifically, the affected versions do not adequately enforce:

1. Signature Validation: The module fails to properly validate that SAML assertions are cryptographically signed by the expected Identity Provider, allowing forged or unsigned assertions to be accepted.

2. Binding Checks: Insufficient verification of SAML protocol bindings allows attackers to manipulate the authentication flow, potentially injecting malicious assertions through unexpected channels.

These implementation gaps violate the core security principles of SAML authentication, where signature verification ensures message integrity and authenticity.

Attack Vector

An attacker can exploit this vulnerability by intercepting or crafting SAML responses that bypass the signature validation mechanisms. The attack flow typically involves:

1. Reconnaissance: Identifying target applications using vulnerable Mendix SAML module versions in specific SSO configurations
2. SAML Response Manipulation: Crafting malicious SAML assertions with modified identity claims or forged signatures
3. Account Hijacking: Submitting the malicious SAML response to the Service Provider, which accepts the invalid assertion due to insufficient validation
4. Unauthorized Access: Gaining access to victim accounts without valid credentials

The vulnerability affects SAML-based authentication flows where the Mendix application acts as a Service Provider. Attackers with network access to the authentication endpoints can potentially impersonate any user within the SSO trust domain.

For detailed technical information about the vulnerability mechanism, refer to the Siemens Security Advisory SSA-395458.

Detection Methods for CVE-2025-40758

Indicators of Compromise

• Unusual SAML authentication events with malformed or unsigned assertions in application logs
• Authentication successes from unexpected IP addresses or geographic locations without corresponding legitimate IdP activity
• Multiple account access patterns indicating session hijacking or unauthorized lateral movement
• SAML response timestamps that fall outside expected validity windows

Detection Strategies

• Implement SAML assertion logging to capture and analyze all authentication requests for anomalous signature validation failures
• Deploy network monitoring to detect unusual traffic patterns to SAML endpoints, including malformed SAML payloads
• Configure alerting for successful authentications that lack corresponding IdP-side audit trail entries
• Monitor for multiple concurrent sessions or rapid session creation across different user accounts

Monitoring Recommendations

• Enable verbose logging for the Mendix SAML module to capture signature validation events and binding checks
• Implement correlation rules in SIEM platforms to identify authentication anomalies between IdP and SP logs
• Establish baseline behavior for SAML authentication patterns and alert on statistical deviations
• Configure real-time alerts for authentication events involving privileged or sensitive user accounts

How to Mitigate CVE-2025-40758

Immediate Actions Required

• Upgrade Mendix SAML module to patched versions immediately: V4.0.3+ for Mendix 10.12, V4.1.2+ for Mendix 10.21, or V3.6.21+ for Mendix 9.24
• Audit all SSO configurations to identify potentially affected deployments and prioritize remediation
• Review authentication logs for signs of exploitation or unauthorized access attempts
• Implement network-level access controls to restrict access to SAML endpoints from trusted networks only

Patch Information

Siemens has released security updates for the Mendix SAML module addressing this vulnerability. Organizations should upgrade to the following minimum versions:

For complete patch details and download information, refer to the Siemens Security Advisory SSA-395458.

Workarounds

• If immediate patching is not possible, consider temporarily disabling SAML-based SSO and reverting to alternative authentication mechanisms
• Implement additional authentication factors (MFA) to reduce the impact of potential account compromise
• Deploy web application firewall (WAF) rules to inspect and validate SAML traffic for malformed or suspicious assertions
• Restrict SAML authentication to known, trusted network segments while awaiting patch deployment

# Verify current Mendix SAML module version
# Check your project's dependencies/modules for the installed version
# Example: Navigate to your Mendix project directory and review module metadata

# Recommended: Update to patched versions via Mendix Marketplace
# Mendix 10.12: Update to Mendix SAML module V4.0.3 or later
# Mendix 10.21: Update to Mendix SAML module V4.1.2 or later
# Mendix 9.24: Update to Mendix SAML module V3.6.21 or later