A critical denial of service vulnerability in Entr'ouvert Lasso 2.5.1 allows unauthenticated remote attackers to disrupt service availability.

This vulnerability is caused by a NULL pointer dereference within the lasso_provider_verify_saml_signature function. An unauthenticated attacker can trigger this condition by submitting a specially crafted, malformed SAML response to the application.

The exploitation of this vulnerability results in a denial of service, which can render critical authentication services unavailable to legitimate users. Given the CVSS score of 7.5, this high-severity flaw poses a significant risk to operational continuity, potentially leading to widespread system downtime for applications relying on Lasso for SAML identity management.

Immediate Action: Contact the vendor or monitor official channels for the release of a security patch addressing this NULL pointer dereference.

Proactive Monitoring: Inspect server and application logs for repeated, malformed SAML requests or unexpected service crashes associated with the lasso_provider_verify_saml_signature function.

Compensating Controls: Deploy a Web Application Firewall (WAF) with rules configured to validate and filter incoming SAML assertions, blocking malformed XML structures before they reach the backend processing logic.

Public Exploit Available: No

This vulnerability presents a clear risk to service availability and should be prioritized for remediation. Organizations currently running Entr'ouvert Lasso 2.5.1 should immediately restrict access to SAML endpoints if possible and maintain a high state of readiness to apply security updates as soon as they are made available by the vendor.