CVE-2025-65498 is a vulnerability identified in version 4.3.5 of the OISM libcoap library, specifically within the coap_dtls_generate_cookie() function located in the src/coap_openssl.c source file. The issue is a NULL pointer dereference triggered during the DTLS handshake process. When a remote attacker sends a specially crafted DTLS handshake message, the function SSL_get_SSL_CTX() may return a NULL pointer. The libcoap code does not properly check for this NULL return value before dereferencing it, leading to a crash of the process handling the DTLS connection. This results in a denial of service (DoS) condition, as the affected service becomes unavailable or unstable. The vulnerability requires no privileges to exploit but does require user interaction in the form of the handshake attempt. The CVSS v3.1 base score is 4.3, reflecting a medium severity level primarily due to the impact on availability without affecting confidentiality or integrity. No patches or fixes have been released yet, and there are no known exploits in the wild. The vulnerability falls under CWE-476 (NULL Pointer Dereference), a common programming error that can lead to crashes and DoS. The affected component, libcoap, is widely used in constrained IoT environments for CoAP protocol communication secured by DTLS via OpenSSL. This makes embedded devices and IoT systems that rely on libcoap potentially vulnerable to remote DoS attacks that could disrupt communications or device availability.

The primary impact of CVE-2025-65498 is denial of service, which affects the availability of systems using libcoap 4.3.5 with OpenSSL DTLS support. For European organizations, this could disrupt IoT device communications, sensor networks, and other constrained environment applications that depend on CoAP over DTLS. Critical infrastructure sectors such as energy, manufacturing, healthcare, and smart city deployments that utilize libcoap-enabled devices may experience service outages or degraded performance. Although the vulnerability does not compromise confidentiality or integrity, the loss of availability can have cascading effects, including operational downtime, loss of telemetry data, and interruption of automated control systems. The lack of authentication requirements for exploitation increases the risk of opportunistic attacks from remote adversaries. However, the need for user interaction (a DTLS handshake attempt) somewhat limits automated mass exploitation. The absence of known exploits in the wild currently reduces immediate risk, but the vulnerability should be considered a moderate threat to IoT and embedded system reliability in Europe.

1. Monitor official libcoap repositories and security advisories for patches addressing CVE-2025-65498 and apply updates promptly once available. 2. Implement network-level filtering to restrict DTLS handshake attempts from untrusted or unknown sources, reducing exposure to crafted handshake messages. 3. Employ intrusion detection/prevention systems (IDS/IPS) capable of detecting anomalous DTLS handshake patterns indicative of exploitation attempts. 4. Where possible, isolate critical IoT devices using libcoap in segmented network zones with strict access controls to limit attack surface. 5. Conduct thorough testing of libcoap-based applications to identify and handle NULL pointer returns gracefully, potentially contributing patches upstream. 6. Maintain robust logging and monitoring of DTLS handshake failures to detect potential exploitation attempts early. 7. Consider fallback or alternative communication protocols temporarily if patching is delayed and risk is high. 8. Educate operational technology (OT) and IoT teams about this vulnerability to ensure rapid response and mitigation implementation.