CVE-2026-8720: wc_Blake2bHmacFinal and wc_Blake2sHmacFinal discard the message when the key length exceeds the block size, pr

Routine

HIGH 7.5REMOTEUPGRADE

CVE-2026-8720 is a high-severity flaw (CVSS 7.5) affecting wolfssl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 A

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 95%)
CISA exploited list	No
Weakness	CWE-354
Published	2026-06-25
Last modified	2026-06-27

Publisher (CNA): wolfSSL Inc. · Vendor: wolfssl

Last updated 2026-06-27 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-25 22:17 UTCPublished CVE record published
2026-06-27 19:43 UTCUpdated Record last modified

wolfssl wolfssl UPGRADE

Affected: >= 5.9.0 and < 5.9.2

Fixed in: 5.9.2

Safe to downgrade to: a release before 5.9.0

1. Check installed version

apt-cache policy wolfssl || rpm -q wolfssl || wolfssl --version

2. UPGRADE to 5.9.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade wolfssl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade wolfssl

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 5.9.0 (Debian / Ubuntu)

apt-cache madison wolfssl sudo apt install wolfssl=<VERSION_BEFORE_5.9.0> sudo apt-mark hold wolfssl

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list wolfssl sudo dnf downgrade wolfssl-<VERSION_BEFORE_5.9.0> sudo dnf versionlock add wolfssl

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-8720?

wolfssl: upgrade to 5.9.2. Exact commands for each OS are on this page.

Is CVE-2026-8720 being exploited?

CVE-2026-8720 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-8720 affect?

CVE-2026-8720 affects wolfssl. Severity is high (CVSS 7.5). 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

How urgent is CVE-2026-8720?

Priority 32/100. High severity; Remotely exploitable, no login, no user action

Software pages

wolfSSL vulnerabilities

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References

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