This vulnerability involves an out‑of‑bounds read in the XMSS and XMSS^MT signature verification code of liboqs. If a caller supplies a signature buffer that is shorter than the expected size for the chosen parameter set, the function does not check the length and reads beyond the buffer. The leaked bytes are only used as input to an internal hash, so they cannot be retrieved by an attacker. The primary observable effect is a potential crash of the verifying process if the read crosses into unmapped memory, resulting in a denial‑of‑service condition.

The issue affects the open‑quantum‑safe liboqs library for any version earlier than 0.16.0. Applications that link against these older releases are susceptible.

The CVSS score of 5.3 indicates a moderate severity, and the vulnerability is not listed in the CISA KEV catalogue. Because the exploit requires an attacker to supply malformed signature data to the verification routine, the risk is primarily local or remote depending on whether the library is exposed through an application. There is no known exploitation that leads to information disclosure or code execution; the immediate risk is a disabling denial‑of‑service of the verifying process. Updating to 0.16.0 removes the flaw, and until then protective coding practices such as validating signature lengths can mitigate the risk.