CVE-2025-11933 is a vulnerability identified in the wolfSSL library, specifically affecting version 5.8.2 and earlier. The issue stems from improper input validation (CWE-20) during the parsing of the TLS 1.3 ClientHello message, particularly the Client Key Share (CKS) extension. The TLS 1.3 protocol uses the CKS extension to negotiate cryptographic parameters for secure communication. The vulnerability occurs when the wolfSSL parser encounters duplicate CKS extensions within a single ClientHello message. Due to insufficient validation, this crafted message can trigger a denial-of-service condition by causing the wolfSSL process to crash or become unresponsive. The attack vector is network-based, requiring no authentication or user interaction, making it accessible to remote attackers. The vulnerability affects multiple platforms that use wolfSSL for TLS 1.3 communications, including embedded systems, IoT devices, and applications relying on wolfSSL for secure transport. Although no public exploits have been reported, the flaw presents a risk of service disruption, which could be leveraged in targeted denial-of-service attacks. The CVSS 4.0 base score of 2.3 reflects a low severity, primarily due to the limited impact on confidentiality and integrity, and the requirement for crafted network traffic without privilege escalation. No patches or fixes are currently linked, so mitigation may involve updating to a fixed version once available or applying network-level protections to detect and block malformed ClientHello messages with duplicate CKS extensions.

For European organizations, the primary impact of CVE-2025-11933 is the potential for denial-of-service attacks against services using vulnerable wolfSSL versions. This could disrupt secure communications, affecting availability of critical applications, especially those relying on TLS 1.3 for encrypted data exchange. Industries such as telecommunications, finance, healthcare, and critical infrastructure that utilize embedded devices or IoT systems with wolfSSL are at higher risk of service interruptions. Although the vulnerability does not compromise confidentiality or integrity, availability disruptions could lead to operational downtime, loss of customer trust, and regulatory scrutiny under frameworks like GDPR if service continuity is impacted. The low severity suggests limited risk of widespread exploitation, but targeted attacks against high-value or critical systems could cause localized outages. European organizations with extensive use of wolfSSL in network appliances, industrial control systems, or secure communication endpoints should assess their exposure and readiness to respond to potential DoS attempts.

To mitigate CVE-2025-11933, organizations should first inventory all systems and applications using wolfSSL version 5.8.2 or earlier. Immediate steps include: 1) Monitoring network traffic for anomalous TLS ClientHello messages containing duplicate CKS extensions using advanced intrusion detection/prevention systems (IDS/IPS) or custom TLS parsers. 2) Implementing rate limiting and connection throttling on TLS endpoints to reduce the impact of malformed handshake attempts. 3) Applying network segmentation to isolate vulnerable devices and limit exposure to untrusted networks. 4) Coordinating with wolfSSL vendors or maintainers to obtain patches or updated versions that address this vulnerability as soon as they become available. 5) Testing and deploying updated wolfSSL versions in development and staging environments before production rollout. 6) Educating security teams about this specific attack vector to improve incident detection and response. 7) Considering fallback TLS configurations or alternative libraries temporarily if patching is delayed. These targeted measures go beyond generic advice by focusing on detection of malformed ClientHello messages and proactive network controls tailored to the vulnerability’s characteristics.