CVE-2025-46705 is a denial of service vulnerability identified in Entr'ouvert Lasso versions 2.5.1 and 2.8.2, related to a reachable assertion failure (CWE-617) in the g_assert_not_reached function. Lasso is a software product used for SAML (Security Assertion Markup Language) processing, commonly employed in federated identity and single sign-on (SSO) solutions. The vulnerability is triggered when the software processes a specially crafted SAML assertion response that violates expected conditions, causing the assertion to fail and the application to abort execution. This results in a denial of service condition, as the service handling authentication requests becomes unavailable. The vulnerability can be exploited remotely by an unauthenticated attacker who sends a malformed SAML response to a vulnerable Lasso instance. The CVSS v3.1 base score is 7.5, reflecting network attack vector, low attack complexity, no privileges or user interaction required, and a high impact on availability only. There is no impact on confidentiality or integrity. No public exploits or active exploitation have been reported to date. The vulnerability was reserved in May 2025 and published in November 2025. No patches or mitigations have been officially released at the time of this report, but the vendor is expected to address it. This vulnerability highlights the risks in SAML processing libraries where improper handling of unexpected input can lead to service disruption.

For European organizations, the primary impact of CVE-2025-46705 is the potential denial of service of authentication services relying on Entr'ouvert Lasso. This can disrupt user access to critical applications and services that depend on SAML-based single sign-on, affecting business continuity and operational efficiency. Sectors such as finance, healthcare, government, and telecommunications, which often use federated identity management, are particularly vulnerable. The unavailability of authentication services can lead to operational downtime, increased support costs, and potential regulatory compliance issues related to service availability. Although confidentiality and integrity are not directly impacted, the disruption of authentication services can indirectly affect security posture by forcing fallback to less secure authentication methods or manual processes. The lack of known exploits reduces immediate risk but does not eliminate the threat, especially given the ease of exploitation without authentication or user interaction. Organizations with internet-facing SAML endpoints or those that accept SAML responses from external identity providers are at higher risk.

Until an official patch is released by Entr'ouvert, European organizations should implement the following mitigations: 1) Deploy network-level filtering or web application firewall (WAF) rules to detect and block malformed or suspicious SAML assertion responses, focusing on anomalies in SAML XML structure or unexpected assertion content. 2) Restrict access to SAML endpoints to trusted identity providers and known IP ranges to reduce exposure to unauthenticated attackers. 3) Monitor authentication service logs for unusual or malformed SAML responses that could indicate exploitation attempts. 4) Implement redundancy and failover mechanisms for authentication services to minimize downtime in case of denial of service. 5) Engage with the vendor for timely updates and apply patches promptly once available. 6) Review and harden SAML processing configurations to enforce strict schema validation and reject unexpected inputs. 7) Conduct penetration testing and vulnerability assessments focusing on SAML endpoints to identify potential exploitation vectors. These steps go beyond generic advice by focusing on proactive filtering, access control, and monitoring specific to SAML assertion handling.