CVE-2026-8720CWE-354

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

Medium · published June 25, 2026

CVSS v4.0
5.9
EPSS
0%
Percentile
4.6
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
5.9 · MEDIUM
Vector
CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
EPSS
0.00158 · 4.6th percentile
Weakness
CWE-354 · Improper Validation of Integrity Check Value
Published
2026-06-25T21:18Z
EPSS history
Timeline
  • 25 JUN 21:18Z
    HMAC-BLAKE2 final discards message when key length exceeds block size
    cvelistv5