HMAC zero-length tag forgery in EVP_DigestVerifyFinal, where a zero-length tag could be accepted as valid during HMAC verification. In the OpenSSL-compatibility HMAC verify path the supplied signature length was only checked as not exceeding the MAC length, so a zero-length or otherwise truncated tag could pass verification. The fix requires the supplied tag length to exactly equal the MAC length and rejects a zero-length MAC, so a forged short or empty tag is no longer accepted.
{
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/6xxx/CVE-2026-6331.json",
"cna_assigner": "wolfSSL",
"cwe_ids": [
"CWE-347"
]
}