CVE-2026-6331

What it is

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.

At a glance

Exploitability

Can be exploited locally on the machine without logging in. Limited direct impact.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-06-25 22:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-27 19:48 UTC Last updatedMost recent change to the record

Details

Published

2026-06-25 22:17 UTC

Last modified

2026-06-27 19:48 UTC

Exploit probability

0.2% · EPSS, next 30 days

Weakness

CWE-347

Record status

Analyzed

Affected

• Wolfssl < 5.9.2

Attack profile CVSS 4.0 · 2.1

Attack vector

Local

Complexity

High

Attack requirements

Present

Privileges needed

None

User interaction

None

Confidentiality

None

Integrity

Low

Availability

None