Vulnerability · Published Jun 25, 2026 · Assigned by wolfSSL
CVE-2026-6331HMAC zero-length tag forgery in EVP_DigestVerifyFinal
Low 2.1
In plain English
A low-severity security flaw in wolfSSL from wolfSSL. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.24 | wolfssl | 5.9.2-r0 | ALPINE-CVE-2026-6331 |
| Debian:12 | wolfssl | 5.5.4-2+deb12u3 | DEBIAN-CVE-2026-6331 |
| Debian:13 | wolfssl | 5.7.2-0.1+deb13u2 | DEBIAN-CVE-2026-6331 |
| Ubuntu:22.04:LTS | wolfssl | no fix listed | UBUNTU-CVE-2026-6331 |
| Ubuntu:24.04:LTS | wolfssl | no fix listed | UBUNTU-CVE-2026-6331 |
| Ubuntu:25.10 | wolfssl | no fix listed | UBUNTU-CVE-2026-6331 |
| Ubuntu:26.04:LTS | wolfssl | no fix listed | UBUNTU-CVE-2026-6331 |
| Ubuntu:26.10 | wolfssl | no fix listed | UBUNTU-CVE-2026-6331 |
Affected products (as reported)
Weakness: CWE-347 · Vector: CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N