CVE-2025-49087 is a medium-severity vulnerability identified in Mbed TLS versions 3.6.1 through 3.6.3, specifically affecting the block cipher padding removal process when using PKCS#7 padding mode. The vulnerability arises from a timing discrepancy during the removal of padding bytes after decryption. This timing difference creates a covert timing channel (classified under CWE-385), which can be exploited by an attacker to infer plaintext data. Essentially, by measuring the time taken to process different ciphertext inputs, an attacker can gradually recover sensitive plaintext information without requiring any authentication or user interaction. The vulnerability is network exploitable (AV:N) but requires high attack complexity (AC:H), meaning the attacker must have precise timing measurement capabilities and conditions to successfully exploit the flaw. The vulnerability does not impact integrity or availability but results in partial confidentiality loss. The scope is considered changed (S:C) because the vulnerability affects the confidentiality of data beyond the immediate component. No known exploits are currently reported in the wild, and no official patches have been linked yet, although it is expected that future Mbed TLS releases will address this issue.

For European organizations, this vulnerability poses a risk primarily to systems and applications that utilize Mbed TLS for cryptographic operations, especially those employing PKCS#7 padding in block cipher modes. Since Mbed TLS is widely used in embedded systems, IoT devices, and lightweight applications, sectors such as industrial control, telecommunications, healthcare devices, and smart infrastructure could be affected. The ability to recover plaintext through timing analysis could lead to leakage of sensitive data such as encryption keys, authentication tokens, or confidential communications. This is particularly concerning for organizations handling regulated data under GDPR, where confidentiality breaches can lead to significant legal and financial consequences. However, the high complexity of exploitation and absence of known active exploits reduce the immediate risk. Still, targeted attackers with advanced capabilities could leverage this vulnerability in espionage or data theft campaigns against critical European infrastructure or enterprises.

Organizations should prioritize upgrading Mbed TLS to version 3.6.4 or later once available, as this will likely contain the fix for the timing discrepancy in padding removal. In the interim, developers should consider disabling or avoiding the use of PKCS#7 padding mode in block cipher operations if feasible, or implement constant-time padding removal routines to eliminate timing side channels. Network defenses such as intrusion detection systems should be tuned to detect abnormal timing-based probing patterns, although this is challenging. Additionally, organizations should conduct code audits and penetration testing focusing on cryptographic implementations to identify and remediate similar timing side channels. For embedded and IoT devices where updates are difficult, compensating controls such as network segmentation, strict access controls, and monitoring for anomalous traffic should be enforced to reduce exposure. Finally, raising awareness among development teams about side-channel vulnerabilities and secure cryptographic coding practices is essential to prevent recurrence.