CVE-2026-6331: wolfSSL

High severity, CVSS 7.5. EPSS: 0.2% chance of exploitation in the next 30 days.

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.

Affected products

• wolfSSL wolfSSL: from 3.15.5, before 5.9.2 (fixed in 5.9.2)

Published 2026-06-25. Last modified 2026-06-27.