HIGHVulnerability
Verified
Global
NVD HIGH: CVE-2026-6331 — HMAC zero-length tag forgery in EVP_DigestVerifyFinal, where a zero-length tag c...
·Source: NIST NVD
Updated:
Executive Summary
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
Analysis
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. CVSS Score: 7.5. Published: 2026-06-25T22:17:03.010.