mbed TLS up to 3.6.3 mbedtls_lms_verify missing cryptographic step

Summaryinfo

A vulnerability marked as problematic has been reported in mbed TLS up to 3.6.3. The affected element is the function mbedtls_lms_verify. The manipulation leads to missing cryptographic step. This vulnerability is traded as CVE-2025-49600. It is possible to launch the attack on the physical device. There is no exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in mbed TLS up to 3.6.3 and classified as problematic. This issue affects the function mbedtls_lms_verify. The manipulation with an unknown input leads to a missing cryptographic step vulnerability. Using CWE to declare the problem leads to CWE-325. The product does not implement a required step in a cryptographic algorithm, resulting in weaker encryption than advertised by the algorithm. Impacted is integrity. The summary by CVE is:

In MbedTLS 3.3.0 before 3.6.4, mbedtls_lms_verify may accept invalid signatures if hash computation fails and internal errors go unchecked, enabling LMS (Leighton-Micali Signature) forgery in a fault scenario. Specifically, unchecked return values in mbedtls_lms_verify allow an attacker (who can induce a hardware hash accelerator fault) to bypass LMS signature verification by reusing stale stack data, resulting in acceptance of an invalid signature. In mbedtls_lms_verify, the return values of the internal Merkle tree functions create_merkle_leaf_value and create_merkle_internal_value are not checked. These functions return an integer that indicates whether the call succeeded or not. If a failure occurs, the output buffer (Tc_candidate_root_node) may remain uninitialized, and the result of the signature verification is unpredictable. When the software implementation of SHA-256 is used, these functions will not fail. However, with hardware-accelerated hashing, an attacker could use fault injection against the accelerator to bypass verification.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2025-49600 since 06/06/2025. The exploitation is known to be difficult. An attack has to be approached locally. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1600 for this issue.

Upgrading to version 3.6.4 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2025-20080). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Name

• mbed TLS

Version

• 3.6.0
• 3.6.1
• 3.6.2
• 3.6.3

CPE 2.3info

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CPE 2.2info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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