CVE-2025-46404: Entrouvert Lasso DOS Vulnerability

CVE-2025-46404 Overview

A denial of service vulnerability exists in the lasso_provider_verify_saml_signature functionality of Entr'ouvert Lasso 2.5.1. This vulnerability allows an attacker to send a specially crafted SAML response that triggers a null pointer dereference, causing the application to crash and become unavailable. The attack can be executed remotely over the network without requiring authentication or user interaction, making it particularly concerning for organizations relying on Lasso for SAML-based authentication.

Critical Impact

Attackers can disrupt authentication services by sending malformed SAML responses, potentially locking users out of federated identity systems and causing widespread service unavailability.

Affected Products

• Entr'ouvert Lasso 2.5.1
• Applications and services integrating the Lasso SAML library
• Identity providers and service providers using Lasso for SAML authentication

Discovery Timeline

• 2025-11-05 - CVE-2025-46404 published to NVD
• 2025-11-07 - Last updated in NVD database

Technical Details for CVE-2025-46404

Vulnerability Analysis

This vulnerability is classified as CWE-476 (NULL Pointer Dereference), occurring within the SAML signature verification routine. When processing SAML responses, the lasso_provider_verify_saml_signature function fails to properly validate input parameters before dereferencing pointers. An attacker can exploit this weakness by crafting a malicious SAML response with specific malformed elements that cause the function to attempt to access memory through a null pointer, resulting in an immediate application crash.

The attack requires no authentication and can be triggered remotely, making it accessible to any attacker who can send SAML responses to the affected service. While this vulnerability does not compromise confidentiality or integrity, the availability impact is severe as it can completely disrupt authentication services.

Root Cause

The root cause of this vulnerability lies in insufficient input validation within the lasso_provider_verify_saml_signature function. The code path that handles SAML signature verification does not adequately check for null or malformed elements before attempting to process them. When a specially crafted SAML response is received, the function proceeds to dereference a pointer that has not been properly initialized or has been set to null due to the malformed input structure.

Attack Vector

The vulnerability is exploited over the network by sending a malformed SAML response to a service utilizing the vulnerable Lasso library. The attacker does not need valid credentials or prior access to the target system. The attack flow involves:

1. Identifying a target service that uses Entr'ouvert Lasso for SAML authentication
2. Crafting a SAML response with malformed signature elements designed to trigger the null pointer condition
3. Sending the malicious SAML response to the target service's SAML endpoint
4. The lasso_provider_verify_saml_signature function processes the malformed input and crashes due to the null pointer dereference

The vulnerability manifests in the SAML signature verification routine when processing malformed responses. Technical details about the specific malformed SAML structure that triggers this condition can be found in the Talos Intelligence Vulnerability Report.

Detection Methods for CVE-2025-46404

Indicators of Compromise

• Unexpected crashes or restarts of services using the Lasso SAML library
• Application crash logs showing segmentation faults in lasso_provider_verify_saml_signature
• Abnormal SAML response patterns or malformed XML structures in authentication logs
• Service unavailability coinciding with SAML authentication attempts

Detection Strategies

• Monitor application logs for null pointer dereference exceptions in Lasso library functions
• Implement network monitoring to detect anomalous SAML response payloads with unusual or malformed structures
• Deploy intrusion detection rules to identify repeated SAML authentication failures followed by service crashes
• Use application performance monitoring to alert on unexpected service restarts

Monitoring Recommendations

• Enable verbose logging for SAML authentication processes to capture malformed request details
• Configure alerting for service availability degradation on authentication endpoints
• Implement rate limiting on SAML endpoints to slow potential exploitation attempts
• Monitor for patterns of malformed SAML responses from specific source IPs

How to Mitigate CVE-2025-46404

Immediate Actions Required

• Review your environment for applications using Entr'ouvert Lasso version 2.5.1
• Monitor the Talos Intelligence Vulnerability Report for patch availability
• Implement network-level filtering to validate SAML response structures before they reach the application
• Consider implementing additional authentication redundancy to maintain service availability

Patch Information

Organizations should monitor Entr'ouvert's official channels and the Talos Intelligence advisory for patch release information. Once a security update is available, apply it immediately to all affected systems. Ensure that all applications integrating the Lasso library are updated to the patched version.

Workarounds

• Deploy a web application firewall (WAF) with rules to validate SAML response structure and reject malformed requests
• Implement input validation at the application layer before passing SAML responses to the Lasso library
• Use network segmentation to limit exposure of SAML endpoints to trusted networks where possible
• Configure automatic service restart mechanisms to minimize downtime if exploitation occurs

# Example: Configure service monitoring and auto-restart
# systemd service configuration for automatic restart
[Service]
Restart=always
RestartSec=5
WatchdogSec=30