# CVE-2026-6731: wolfSSL X.509 name constraint bypass in Subject Common Name

Source: https://junglewise.ai/threats/cve-2026-6731-wolfssl-x-509-name-constraint-bypass-in-subject-common-name  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-25. Updated: 2026-06-25  
License: CC BY 4.0 with a link back

CVE-2026-6731 · Severity: info · CVSS 6 · Published 2026-06-25

wolfSSL is a security library used to establish encrypted connections for applications and embedded devices. A vulnerability was found where the library fails to properly check certain security restrictions on digital certificates if they do not contain modern 'Subject Alternative Name' fields. This could allow a malicious or compromised certificate authority to issue certificates that bypass intended security boundaries, potentially leading to unauthorized connections being accepted as valid.

Technologies: [Wolfssl](https://junglewise.ai/threats/technologies/wolfssl). Vendors: [Wolfssl](https://junglewise.ai/threats/vendors/wolfssl).

## Quick answers

**Is CVE-2026-6731 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-6731 being exploited in the wild.

**How severe is CVE-2026-6731?** Informational severity, with a CVSS score of 6, published 25 June 2026.

**Which products and versions are affected?** Wolfssl 3.9.10 through 5.9.1.

**Is there a fix for CVE-2026-6731?** A patch was published on 2026-04-19: Fix merged into master branch Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-6731 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-6731?** Check whether you run Wolfssl at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability in wolfSSL's certificate validation logic (CWE-295) allows for a name constraint bypass. When an issuing Certificate Authority (CA) has DNS name constraints defined, wolfSSL only enforces these constraints against the Subject Alternative Name (SAN) extension. If a certificate lacks a SAN extension and instead uses the Subject Common Name (CN) for the DNS identity, the library fails to apply the issuing CA's name constraints to that CN. An attacker with a certificate issued by a constrained CA could use a Subject CN that violates those constraints to impersonate a domain. This issue is fixed in wolfSSL version 5.9.1.

## Affected products

- wolfSSL wolfSSL 3.9.10 through 5.9.1

## Timeline

- 2026-04-14: other: Fix submitted via GitHub pull request
- 2026-04-19: patched: Fix merged into master branch
- 2026-06-25: disclosed: CVE published to NVD

## References

- [https://github.com/wolfSSL/wolfssl](https://github.com/wolfSSL/wolfssl)
- [https://github.com/wolfSSL/wolfssl/pull/10223](https://github.com/wolfSSL/wolfssl/pull/10223)
- [https://www.wolfssl.com/docs/security-vulnerabilities/](https://www.wolfssl.com/docs/security-vulnerabilities/)

## Related threats

- [wolfSSL certificate validation bypass in ConfirmNameConstraints()](https://junglewise.ai/threats/cve-2026-95208-an-issue-in-the-confirmnameconstraints-function-wolfcrypt-src-asn)
- [wolfSSL revocation check bypass with OCSP and CRL](https://junglewise.ai/threats/cve-2026-94417-when-an-application-enables-both-ocsp-and-crl-revocation-checking)
- [wolfSSL TLS 1.2 ChangeCipherSpec message ordering bypass](https://junglewise.ai/threats/cve-2026-93304-a-d-tls-1-2-client-can-accept-a-changecipherspec-message-before)
- [wolfSSL MatchTrustedPeer public key validation bypass](https://junglewise.ai/threats/cve-2026-93302-matchtrustedpeer-ignores-the-public-key-used-leading-to-forged-ca)
- [wolfSSL TLS authentication bypass in Raw Public Key handling](https://junglewise.ai/threats/cve-2026-89136-when-using-rpk-raw-public-key-the-client-side-of-a-tls-1-2-1-3)