What’s Vulnerable › Vulnerabilities

CVE-2026-6331: HMAC zero-length tag forgery in EVP_DigestVerifyFinal

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-25 · updated 2026-06-27
• Weakness: CWE-347

Description

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: from 3.15.5 before 5.9.2 — fixed in 5.9.2

How to fix

Upgrade to a fixed version: wolfSSL 5.9.2. Check the vendor advisory for mitigations.

References

• https://github.com/wolfSSL/wolfssl/pull/10192
• https://www.wolfssl.com/docs/security-vulnerabilities/

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