CVE-2025-11933 is a vulnerability classified under CWE-20 (Improper Input Validation) affecting the wolfSSL library, specifically versions 5.8.2 and earlier. The issue arises in the TLS 1.3 ClientHello message parsing logic, where the CKS (Client Key Share) extension is improperly validated. The vulnerability allows a remote unauthenticated attacker to send a ClientHello message containing duplicate CKS extensions. This malformed input can cause the wolfSSL library to mishandle the message, leading to a denial-of-service (DoS) condition by crashing or hanging the TLS service. The flaw affects multiple platforms since wolfSSL is a widely used lightweight SSL/TLS library embedded in various devices and applications, including IoT devices, industrial control systems, and network appliances. The CVSS 4.0 score is 2.3, reflecting low severity due to the limited impact (availability only), no confidentiality or integrity compromise, and the requirement for some privileges (low privileges) to exploit. No user interaction is needed, and the attack vector is network-based. Currently, no public exploits or patches are available, but the vulnerability is publicly disclosed and should be addressed promptly. The root cause is insufficient validation of the number of CKS extensions in the ClientHello message, violating protocol expectations and causing the TLS handshake to fail or the service to crash.

The primary impact of CVE-2025-11933 is a denial-of-service condition affecting availability of services using vulnerable wolfSSL versions. For European organizations, this could disrupt critical communications secured by TLS, especially in sectors relying on embedded devices and IoT systems where wolfSSL is prevalent. Industrial control systems, telecommunications infrastructure, and network appliances could experience service outages or degraded performance. Although the vulnerability does not expose sensitive data or allow unauthorized access, the resulting downtime could lead to operational disruptions, financial losses, and reputational damage. Organizations with large-scale deployments of wolfSSL in critical environments are at higher risk. The low CVSS score indicates limited severity, but the ease of triggering DoS remotely without authentication means attackers could exploit this vulnerability to cause targeted disruptions. In Europe, where digital infrastructure and IoT adoption are significant, the impact could be notable if unpatched systems are widespread.

1. Monitor wolfSSL vendor advisories closely and apply security patches or updated versions as soon as they become available to address CVE-2025-11933. 2. In the absence of an immediate patch, implement network-level filtering or intrusion prevention rules to detect and block TLS ClientHello messages containing duplicate CKS extensions. This can be done by enhancing TLS inspection capabilities on firewalls or dedicated security appliances. 3. Conduct an inventory of all devices and applications using wolfSSL, especially embedded and IoT devices, to identify vulnerable versions. 4. Where possible, isolate critical systems using vulnerable wolfSSL versions from untrusted networks to reduce exposure. 5. Employ rate limiting and anomaly detection on TLS handshake traffic to mitigate potential DoS attempts exploiting this vulnerability. 6. Engage with device and application vendors to confirm wolfSSL versions in use and request updates if necessary. 7. Incorporate wolfSSL version checks into vulnerability management and patching workflows to ensure timely remediation. 8. Educate network security teams about this specific TLS extension parsing vulnerability to improve detection and response capabilities.