The vulnerability arises in liboqs when it verifies LMS or HSS signatures that are truncated or otherwise malformed. Internally, the function that initializes signature validation performs length checks that do not guarantee the requested fields of the signature remain within the supplied buffer, enabling an over‑read of up to 32 bytes in certain verification paths. A second over‑read of up to eight bytes occurs in the public‑key validation routine in version 0.16.0. Although the read data is not exported outside the library, the corrupted memory access can trigger a crash in the verifier, leading to a denial of service. No data is disclosed, and no attacker-controlled signature is accepted as valid.

The affected component is the open‑quantum‑safe liboqs library, for releases from 0.11.0 through 0.16.0 (inclusive). These builds enable OQS_ENABLE_SIG_STFL_LMS and may be used in applications that rely on LMS or HSS‑LMS signature verification. Users of liboqs 0.16.0 are also vulnerable to a separate over‑read during public key sanity checks. Applications that embed liboqs should review the version they are using and the configuration flags that enable LMS/HSS support.

The CVSS score of 5.3 indicates a medium severity vulnerability. The EPSS score is not available, but because the flaw requires a crafted input to trigger the over‑read, the likelihood of exploitation depends on the exposure of the verification routine to untrusted data. The vulnerability is not currently listed in CISA's KEV catalog. An attacker who can interact with a service that performs LMS/HSS verification could send a malicious truncated signature to cause a crash and deny service. The vulnerability does not provide a path to information disclosure or to forging valid signatures.