7.5

CVE-2026-6331: HMAC zero-length tag forgery in EVP_DigestVerifyFinal

Analyzed
AliasesUBUNTU-CVE-2026-6331DEBIAN-CVE-2026-6331ALPINE-CVE-2026-6331
Published 25-06-2026Last modified 26-06-2026

Vulnerability summary

CVE-2026-6331 is a high (CVSS 7.5) vulnerability in wolfssl. EPSS estimates a 0.19% chance of exploitation in the next 30 days, higher than 8.7% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 2.1, local access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
7.5/10
010
High · v3.1 (NVD)
EPSS score
0.19%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Timeline

  1. 25-06-2026
    PublishedVulnerability first disclosed.
  2. 26-06-2026
    Last modifiedVulnerability information updated.

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.

CVSS metrics

7 scores · 5 sources · 2 versions

EPSS trend

Probability

0.19%

Chance of exploitation in the next 30 days

Percentile

9%

Versus all other CVEs

30-day change

No change 0.00 pp

From 0.19% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: local access, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Alpine1 product
  • wolfssl≥ 3.15.5, < 5.9.2-r0
Debian1 product
  • wolfssl< 5.5.4-2+deb12u3 | < 5.7.2-0.1+deb13u2
Ubuntu1 product
  • wolfsslAll versions (No fix recorded)
Wolfssl1 product
  • wolfssl≥ 3.15.5, ≤ 5.9.1 | ≥ 3.15.5, < 5.9.2

4 vendors · 4 products

References

6 links