How severe is CVE-2026-6331?

CVE-2026-6331 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-6331 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (4th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-6331?

CVE-2026-6331 affects Wolfssl. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-6331?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-6331 have an EU (EUVD) identifier?

Yes. CVE-2026-6331 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-39565.

When was CVE-2026-6331 published?

CVE-2026-6331 was published on 2026-06-25 and last updated on 2026-06-27.

CVE-2026-6331

CVE-2026-6331 is a high-severity vulnerability in Wolfssl with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-347.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v4: 2.1
EPSS exploit prediction: 0% (4th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-39565
Weakness: CWE-347
Affected product: Wolfssl
Published: 2026-06-25
Last modified: 2026-06-27

Description

HMAC zero-length tag forgery in EVP_DigestVerifyFinal, where a zero-length tag could be accepted as valid during HMAC verification. In the OpenSSL-compatibility HMAC verify path the supplied signature length was only checked as not exceeding the MAC length, so a zero-length or otherwise truncated tag could pass verification. The fix requires the supplied tag length to exactly equal the MAC length and rejects a zero-length MAC, so a forged short or empty tag is no longer accepted.

Frequently asked questions

What is CVE-2026-6331?: HMAC zero-length tag forgery in EVP_DigestVerifyFinal, where a zero-length tag could be accepted as valid during HMAC verification. In the OpenSSL-compatibility HMAC verify path the supplied signature length was only checked as not exceeding the MAC length, so a zero-length or otherwise truncated tag could pass verification. The fix requires the supplied tag length to exactly equal the MAC length and rejects a zero-length MAC, so a forged short or empty tag is no longer accepted.
How severe is CVE-2026-6331?: CVE-2026-6331 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-6331 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (4th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-6331?: CVE-2026-6331 affects Wolfssl. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-6331?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-6331 have an EU (EUVD) identifier?: Yes. CVE-2026-6331 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-39565.
When was CVE-2026-6331 published?: CVE-2026-6331 was published on 2026-06-25 and last updated on 2026-06-27.

References

Affected products (1)

cpe:2.3:a:wolfssl:wolfssl:*:*:*:*:*:*:*:*

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