CVE-2025-65502 is a security vulnerability identified in the Cesanta Mongoose networking library prior to version 7.2. The issue arises from a null pointer dereference in the add_ca_certs() function, which is invoked during TLS initialization. Specifically, when the function SSL_CTX_get_cert_store() returns a NULL pointer, the add_ca_certs() function does not properly check for this condition before dereferencing the pointer. This leads to a crash of the application or service using the library, resulting in a denial of service (DoS) condition. The vulnerability can be triggered remotely by an attacker who can initiate a TLS handshake with a vulnerable server or device, causing the TLS initialization process to fail and the application to terminate unexpectedly. No authentication or user interaction is required, making exploitation straightforward in environments where Cesanta Mongoose is used. While no public exploits have been reported yet, the flaw represents a significant risk to availability, especially in embedded systems, IoT devices, or network appliances that rely on this library for secure communications. The lack of a CVSS score indicates that the vulnerability is newly published, but its characteristics suggest a high impact on service continuity. The root cause is inadequate error handling for certificate store retrieval, highlighting the importance of defensive programming practices in security-critical code paths.

The primary impact of CVE-2025-65502 is denial of service due to application crashes during TLS initialization. For European organizations, this can disrupt critical services that depend on Cesanta Mongoose for secure communications, including IoT infrastructure, industrial control systems, and embedded devices in sectors such as manufacturing, energy, and telecommunications. Service outages could lead to operational downtime, loss of productivity, and potential safety risks in industrial environments. Additionally, repeated exploitation attempts could degrade network reliability and increase maintenance costs. Although the vulnerability does not directly compromise confidentiality or integrity, the availability impact alone can have severe consequences, especially for organizations with stringent uptime requirements or those operating critical infrastructure. The absence of known exploits currently limits immediate risk, but the ease of triggering the flaw remotely means attackers could weaponize it rapidly once exploit code becomes available. European entities with extensive IoT deployments or those integrating Cesanta Mongoose in their products are particularly vulnerable to this threat.

To mitigate CVE-2025-65502, organizations should promptly update Cesanta Mongoose to version 7.2 or later, where the null pointer dereference issue has been addressed. If immediate patching is not feasible, implement network-level controls to restrict access to services using the vulnerable library, such as firewall rules or segmentation to limit exposure to untrusted networks. Enhance monitoring to detect abnormal TLS handshake failures or application crashes indicative of exploitation attempts. Developers should audit and improve error handling around SSL_CTX_get_cert_store() calls to ensure null pointers are safely managed, preventing dereferences. For embedded and IoT devices, coordinate with vendors to obtain firmware updates incorporating the fix. Additionally, conduct thorough testing of TLS initialization routines under various certificate store conditions to identify and remediate similar weaknesses. Employ defense-in-depth strategies by combining patch management, network controls, and runtime monitoring to reduce the attack surface and improve incident response capabilities.