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. 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 (trickest)
Affected products and versions
- 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 — CRITICAL · 2026-06-30
Sources
Enriched from CVE.org, FIRST EPSS, public proof-of-concept repositories. Last verified by Threadlinqs on .