# CVE-2026-6091 — wolfSSL

> As of 2026-06-25, CVE-2026-6091 is a Medium-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in wolfSSL, CVSS v4.0 6, EPSS 0.1% (8.4th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-6091, most recently “Multiple WolfSSL Critical Vulnerabilities: Certificate Bypass, RCE, and Post-Quantum Weakening”.

**Last updated:** 2026-06-25

## What is CVE-2026-6091?

Partial-chain certificate verification may accept chains that terminate at a peer-supplied, untrusted intermediate certificate rather than a trusted anchor. An attacker could present a chain that ends at an intermediate they control and have it accepted as valid. This affects the OpenSSL compatibility certificate-path-building path (wolfSSL_X509_verify_cert / X509_STORE, OPENSSL_EXTRA) when the X509_V_FLAG_PARTIAL_CHAIN verify flag is enabled.

The record classifies CVE-2026-6091 under weakness class [CWE-295](https://intel.threadlinqs.com/cwe/CWE-295). 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 107 days ago.

## Severity and exploitation probability

- **CVSS v4.0 base score:** 6 — Medium (derived from score) (`CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **EPSS (FIRST):** 0.1% probability of exploitation in the next 30 days, higher than 8.4% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 5.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-06-25

## Is CVE-2026-6091 being exploited?

Weaponised exploit code for CVE-2026-6091 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 18 in the Threadlinqs vulnerability feed.

- [trickest/cve](https://github.com/trickest/cve/blob/main/2026/CVE-2026-6091.md) (trickest)

## Affected products and versions

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

## How to fix CVE-2026-6091

No vendor patch reference has been recorded for CVE-2026-6091 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-2026-6091

1 tracked threat in the Threadlinqs corpus references CVE-2026-6091, either in the campaign’s CVE list or as an indicator on the campaign record.

- [Multiple WolfSSL Critical Vulnerabilities: Certificate Bypass, RCE, and Post-Quantum Weakening](https://intel.threadlinqs.com/threat/TL-2026-1008) — CRITICAL · 2026-06-30

## Sources

Enriched from CVE.org, FIRST EPSS, public proof-of-concept repositories. Last verified by Threadlinqs on 2026-10-10.

**Vendor advisory and patch**

- [github.com — patch](https://github.com/wolfSSL/wolfssl/pull/10170)

**Other references**

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

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-6091
Full detection coverage and IOCs for threats exploiting CVE-2026-6091 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp