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.
Weakness
The product does not implement a required step in a cryptographic algorithm, resulting in weaker encryption than advertised by the algorithm.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Mbed_tls | Arm | 3.3.0 (including) | 3.6.4 (excluding) |
| Mbedtls | Ubuntu | devel | * |
| Mbedtls | Ubuntu | oracular | * |
| Mbedtls | Ubuntu | plucky | * |
| Mbedtls | Ubuntu | questing | * |
| Mbedtls | Ubuntu | upstream | * |