What’s Vulnerable › Vulnerabilities

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

• 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-354

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.

Affected products

• wolfSSL: from 5.9.0 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/10447
• https://www.wolfssl.com/docs/security-vulnerabilities/

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