CVE-2025-52497 is a medium-severity vulnerability identified in Mbed TLS, a widely used open-source cryptographic library designed for embedded systems and IoT devices. The flaw is an off-by-one error (CWE-193) that leads to a one-byte heap-based buffer underflow during PEM (Privacy Enhanced Mail) parsing. Specifically, the vulnerability exists in the functions mbedtls_pem_read_buffer and two mbedtls_pk_parse functions when processing untrusted PEM input. This buffer underflow occurs because the code incorrectly handles the length of the input data, causing it to read or write one byte outside the allocated heap buffer boundaries. Although the CVSS score is 4.8 (medium), the impact is limited to a loss of availability and confidentiality with no integrity impact, and exploitation requires network access but with high attack complexity and no privileges or user interaction needed. The vulnerability does not currently have known exploits in the wild. The affected versions are all versions before 3.6.4, and no official patch links are provided yet. This vulnerability could potentially be leveraged by attackers to cause application crashes or leak sensitive information from memory buffers, depending on how the PEM parsing is used within the application context. Given that Mbed TLS is embedded in many IoT and embedded devices, the risk is primarily to systems that rely on this library for cryptographic operations, especially those that parse untrusted PEM files or certificates.

For European organizations, the impact of this vulnerability depends on the extent to which Mbed TLS is integrated into their infrastructure, particularly in embedded devices, IoT deployments, and network appliances. Organizations in sectors such as telecommunications, manufacturing (Industry 4.0), smart city infrastructure, and critical infrastructure operators may be at higher risk due to their reliance on embedded systems using Mbed TLS. Exploitation could lead to denial of service conditions or partial leakage of sensitive cryptographic material, potentially undermining confidentiality. While the vulnerability does not allow privilege escalation or code execution directly, disruption or information leakage could affect operational continuity and data privacy compliance under GDPR. The medium severity and lack of known exploits reduce immediate risk, but the widespread use of Mbed TLS in embedded environments means that unpatched devices could be targeted in the future. European organizations with large IoT deployments or embedded device fleets should be vigilant, as these devices often have longer patch cycles and may be harder to update promptly.

European organizations should take the following specific actions: 1) Inventory all devices and applications using Mbed TLS versions prior to 3.6.4, focusing on embedded and IoT devices that handle PEM files or certificates. 2) Apply updates to Mbed TLS to version 3.6.4 or later as soon as patches become available. If direct patching is not feasible, consider isolating affected devices from untrusted networks or restricting access to PEM input sources. 3) Implement strict input validation and sanitization for PEM files or certificate data before processing to reduce the risk of malformed input triggering the vulnerability. 4) Monitor network traffic and logs for unusual crashes or errors related to TLS operations that could indicate exploitation attempts. 5) Engage with device vendors and suppliers to confirm patch availability and deployment plans, especially for embedded devices with limited update capabilities. 6) Incorporate this vulnerability into risk assessments and incident response plans, emphasizing embedded device security and cryptographic library management.