# CVE-2026-6331 — wolfSSL

> As of 2026-06-26, CVE-2026-6331 is a Low-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in wolfSSL, CVSS v4.0 2.1, EPSS 0.1% (1.0th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-6331 as of 2026-06-26; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-06-26

## 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.

The record classifies CVE-2026-6331 under weakness class [CWE-347](https://intel.threadlinqs.com/cwe/CWE-347). 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 102 days ago.

## Severity and exploitation probability

- **CVSS v4.0 base score:** 2.1 — Low (derived from score) (`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`)
- **EPSS (FIRST):** 0.1% probability of exploitation in the next 30 days, higher than 1.0% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 1.1/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-06-25, last modified 2026-06-26

## Is CVE-2026-6331 being exploited?

It currently carries a trending score of 30 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [wolfSSL](https://intel.threadlinqs.com/vendors/wolfssl): wolfSSL

## How to fix CVE-2026-6331

No vendor patch reference has been recorded for CVE-2026-6331 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-6331

No threat campaign in the Threadlinqs corpus currently references CVE-2026-6331, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on 2026-06-28. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [github.com — patch](https://github.com/wolfSSL/wolfssl/pull/10192)

**Other references**

- [wolfssl.com](https://www.wolfssl.com/docs/security-vulnerabilities/)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-6331
Full detection coverage and IOCs for threats exploiting CVE-2026-6331 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp