CVE-2026-6331 HMAC zero-length tag forgery in EVP_DigestVerifyFinal
Attackers can bypass HMAC verification by submitting zero-length tags, allowing forged signatures to be accepted as valid.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-6331?
CVE-2026-6331 is a low-severity vulnerability in Wolfssl Wolfssl, published on 25 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-347
Which versions are affected by CVE-2026-6331?
It affects 1 product.
Products include Wolfssl Wolfssl.
How do I fix CVE-2026-6331?
Apply the vendor's patch.
Is CVE-2026-6331 being exploited?
There is no known exploitation of CVE-2026-6331 in the wild and no public exploit code.
Other vulnerabilities in Wolfssl Wolfssl
Sources
Also known as DEBIAN-CVE-2026-6331, GHSA-5hpf-pc4x-3jcf, JLSEC-2026-749, UBUNTU-CVE-2026-6331.