CVE-2026-8720 HMAC-BLAKE2 final discards message when key length exceeds block size

Medium 5.9 Published 25 Jun 2026 Updated 26 Jun 2026

wolfSSL HMAC-BLAKE2 implementation ignores message data when keys exceed block size, allowing attackers to bypass integrity checks.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Local or same network only
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-8720?

CVE-2026-8720 is a medium-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

wc_Blake2bHmacFinal and wc_Blake2sHmacFinal discard the message when the key length exceeds the block size, producing a MAC that is independent of the input. When the supplied key is longer than the BLAKE2 block size the key-hashing branch reinitialized the running hash state, discarding the accumulated message data, so the resulting MAC depended only on the key and not on the message being authenticated. This bug is specific to the HMAC-BLAKE2 APIs that were added in wolfSSL version 5.9.0.

Weakness: CWE-354

Which versions are affected by CVE-2026-8720?

It affects 1 product.

Products include Wolfssl Wolfssl.

How do I fix CVE-2026-8720?

No fix has been published for CVE-2026-8720 yet. Limit exposure of the affected software until one is available.

Is CVE-2026-8720 being exploited?

There is no known exploitation of CVE-2026-8720 in the wild and no public exploit code.

All Wolfssl Wolfssl vulnerabilities

Sources

Also known as DEBIAN-CVE-2026-8720, GHSA-34qm-63x6-fcm3, UBUNTU-CVE-2026-8720.