CVE-2026-6731Network attack vector

Certificate acceptance via unconstrained Subject Common Name

Published Jun 25, 2026 · Updated Jun 25, 2026

Improper certificate validation in wolfSSL 3.9.10 through 5.9.1 allows remote attackers to bypass issuing-CA DNS name constraints. When a certificate lacks a SAN, certificate-chain validation fails to apply an issuing CA's DNS nameConstraints to the Subject Common Name used as a DNS name. Exploitation requires a constrained issuing CA and a presented certificate whose Common Name falls outside the permitted DNS namespace, causing unauthorized certificate acceptance.

CVSS severity6.0
Medium
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in wolfSSL 3.9.10 through 5.9.1 allows remote attackers to bypass issuing-CA DNS name constraints. When a certificate lacks a SAN, certificate-chain validation fails to apply an issuing CA's DNS nameConstraints to the Subject Common Name used as a DNS name. Exploitation requires a constrained issuing CA and a presented certificate whose Common Name falls outside the permitted DNS namespace, causing unauthorized certificate acceptance.

The record

CVE
CVE-2026-6731
Published
Jun 25, 2026
Updated
Jun 25, 2026
Vendor
wolfSSL
Product
wolfSSL
Classifications
CWE-295, T1553
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Jun 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=3.9.10 <=5.9.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesUnavailable in this record.

What is affected?

wolfSSL · wolfSSLversion=3.9.10 <=5.9.1

Published CVSS scores

6.0wolfSSL Inc.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
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1553Subvert Trust Controls

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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