Executive brief
wolfSSL, a TLS/SSL library used in embedded systems and IoT devices, has a flaw in how it validates certificate names against policy constraints. An attacker can present a certificate with alternative names (like IP addresses) instead of domain names, allowing it to bypass security policies that should restrict which names a certificate can be used for. This could allow forged certificates to be accepted in contexts where they should be rejected.
Technical details
The vulnerability exists in the name-constraint validation logic in wolfSSL's certificate chain verification. A certificate lacking a dNSName Subject Alternative Name (SAN) but containing other SAN types (e.g., registeredID or iPAddress) bypasses the CN-as-DNS fallback check due to incomplete logic that only verifies the altNames field is NULL rather than checking for the absence of dNSName SANs. This is a regression from an incomplete fix to CVE-2026-6731 introduced in version 5.9.2, allowing out-of-scope CNs to be accepted when policy constraints should apply.
Affected products
- wolfSSL wolfSSL 5.9.2 and later (prior to fix)
Timeline
- 2026-09-27: disclosed
- 2026-07-08: patched