CVE-2025-52496 is a vulnerability identified in Mbed TLS, a widely used open-source cryptographic library, specifically affecting versions prior to 3.6.4. The root cause is a race condition in the detection of AESNI (Advanced Encryption Standard New Instructions) capabilities when certain compiler optimizations are applied. This race condition can cause the compiler to remove or modify security-critical code sections, classified under CWE-733, which relates to the removal or modification of security-critical code due to compiler optimizations. The vulnerability manifests in multithreaded programs using Mbed TLS, where the AES key material can be exposed due to improper synchronization during AESNI detection. Additionally, attackers may exploit this flaw to perform Galois/Counter Mode (GCM) forgery attacks, undermining message integrity. The CVSS v3.1 score is 7.8, indicating high severity, with an attack vector limited to local access (AV:L), high attack complexity (AC:H), no privileges required (PR:N), and no user interaction (UI:N). The scope is changed (S:C), meaning the vulnerability affects resources beyond the initially vulnerable component. Confidentiality and integrity impacts are high, while availability is unaffected. No public exploits have been reported yet, but the potential for key extraction and cryptographic forgery poses a serious threat to applications relying on Mbed TLS for secure communications. The vulnerability is particularly relevant for embedded systems, IoT devices, and other multithreaded environments where Mbed TLS is deployed. The lack of patch links suggests that users must monitor official Mbed TLS releases for the fixed version 3.6.4 or later.

For European organizations, the impact of CVE-2025-52496 can be significant, especially for those relying on Mbed TLS in embedded systems, IoT devices, or multithreaded applications that use AES-GCM encryption. Successful exploitation can lead to the extraction of AES keys, compromising the confidentiality of encrypted data, and enable GCM forgery, which undermines data integrity and authenticity. This can result in unauthorized data disclosure, manipulation of sensitive communications, and potential disruption of secure services. Critical sectors such as finance, healthcare, telecommunications, and industrial control systems may face elevated risks due to their reliance on secure cryptographic operations. The high attack complexity and requirement for local access limit remote exploitation but do not eliminate risk, particularly in environments where attackers may gain local foothold or insider access. The absence of known exploits in the wild currently reduces immediate threat levels but does not preclude future exploitation attempts. Organizations failing to update or mitigate this vulnerability may face regulatory and compliance issues under GDPR and other European data protection frameworks if data breaches occur.

1. Upgrade Mbed TLS to version 3.6.4 or later as soon as it becomes available to ensure the race condition and compiler optimization issues are resolved. 2. Review and adjust compiler optimization settings to prevent unsafe code removal or modification, particularly in builds involving AESNI detection and cryptographic routines. 3. Conduct thorough code audits and testing in multithreaded environments to detect potential race conditions or synchronization issues related to cryptographic operations. 4. Limit local access to systems running vulnerable Mbed TLS versions by enforcing strict access controls and monitoring for suspicious activity. 5. Implement runtime protections such as memory protection and process isolation to reduce the risk of key extraction. 6. Monitor vendor advisories and security bulletins for patches and updates related to this vulnerability. 7. For critical systems, consider additional cryptographic layers or hardware security modules (HSMs) to protect key material from software-level vulnerabilities. 8. Educate developers and system administrators about the risks of compiler optimizations affecting security-critical code and encourage secure coding practices.