CVE-2025-65493 is a vulnerability identified in libcoap version 4.3.5, a widely used open-source implementation of the Constrained Application Protocol (CoAP), which is designed for simple devices in constrained environments such as IoT. The flaw exists in the src/coap_openssl.c file, where a NULL pointer dereference occurs due to improper handling of the BIO_get_data() function within DTLS/TLS connection processing. Specifically, when a remote attacker sends a crafted DTLS or TLS connection request, BIO_get_data() may return NULL, and the code does not properly check for this condition before dereferencing the pointer. This leads to a NULL pointer dereference, causing the application to crash and resulting in a denial of service (DoS). The vulnerability can be triggered remotely without requiring any authentication or user interaction, making it relatively easy to exploit. The CVSS v3.1 base score of 7.5 indicates a high severity, primarily due to the impact on availability (denial of service), with an attack vector of network, low attack complexity, and no privileges or user interaction needed. Although no known exploits have been reported in the wild yet, the vulnerability poses a significant risk to systems relying on libcoap for secure communication over DTLS/TLS, especially in IoT and embedded device contexts. The underlying weakness is classified under CWE-476 (NULL Pointer Dereference), a common programming error that can lead to application crashes and service interruptions. Since libcoap is often embedded in constrained devices and gateways, exploitation could disrupt critical communications or services dependent on these protocols.

For European organizations, the primary impact of CVE-2025-65493 is the potential for denial of service attacks against devices and services using libcoap 4.3.5 for DTLS/TLS-secured CoAP communications. This can affect IoT deployments, smart city infrastructure, industrial control systems, and other constrained environments where libcoap is integrated. Disruptions could lead to temporary loss of device availability, impacting operational continuity and potentially safety-critical functions. Given the increasing adoption of IoT and constrained protocols in sectors such as energy, transportation, healthcare, and manufacturing across Europe, the vulnerability could have widespread operational consequences. The lack of required authentication or user interaction lowers the barrier for attackers, increasing the risk of automated or large-scale DoS campaigns. Although confidentiality and integrity are not directly impacted, the availability degradation could indirectly affect business processes and critical infrastructure services. Organizations relying on libcoap in their network stacks or embedded devices should consider this vulnerability a significant risk to service reliability.

To mitigate CVE-2025-65493, European organizations should first identify all systems and devices using libcoap version 4.3.5 or earlier. Since no patch links are currently provided, organizations should monitor the libcoap project for official updates addressing this NULL pointer dereference. In the interim, developers and integrators should review and modify the src/coap_openssl.c code to add robust NULL checks after BIO_get_data() calls to prevent dereferencing NULL pointers. Network-level mitigations include deploying rate limiting and anomaly detection to identify and block suspicious DTLS/TLS connection attempts that could trigger the vulnerability. Segmentation of IoT and constrained device networks can limit exposure. Additionally, organizations should implement comprehensive monitoring to detect service crashes or unusual device behavior indicative of exploitation attempts. For critical environments, consider fallback or redundancy mechanisms to maintain availability during potential attacks. Engaging with device vendors to ensure timely firmware or software updates is also essential. Finally, applying defense-in-depth strategies such as secure coding reviews and fuzz testing for similar vulnerabilities in protocol implementations can reduce future risks.