CVE-2025-49600: Medium severity Arm MbedTLS vulnerability

In MbedTLS 3.3.0 before 3.6.4, mbedtlslmsverify 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 mbedtlslmsverify 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 mbedtlslmsverify, the return values of the internal Merkle tree functions createmerkleleafvalue and createmerkleinternalvalue are not checked. These functions return an integer that indicates whether the call succeeded or not. If a failure occurs, the output buffer (Tccandidaterootnode) 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.