CVE-2026-8720
Received Received - Intake
HMAC-BLAKE2 Key-Length Handling Flaw in wolfSSL

Publication date: 2026-06-25

Last updated on: 2026-06-25

Assigner: wolfSSL Inc.

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.
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Meta Information
Published
2026-06-25
Last Modified
2026-06-25
Generated
2026-06-26
AI Q&A
2026-06-26
EPSS Evaluated
N/A
NVD
CVE-2026-8720
EUVD
EUVD-2026-39579
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
wolfssl wolfssl From 5.9.0 (inc)
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-354 The product does not validate or incorrectly validates the integrity check values or "checksums" of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission.
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Executive Summary

This vulnerability occurs in the wc_Blake2bHmacFinal and wc_Blake2sHmacFinal functions of wolfSSL's HMAC-BLAKE2 APIs introduced in version 5.9.0. When the key length exceeds the BLAKE2 block size, these functions discard the message data during processing, causing the resulting Message Authentication Code (MAC) to depend only on the key and not on the actual message being authenticated.

Impact Analysis

Because the MAC produced is independent of the input message when the key is too long, an attacker could exploit this to bypass message authentication. This undermines the integrity guarantees of the HMAC, potentially allowing unauthorized modification or spoofing of messages without detection.

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