Summary
A certificate validation flaw in wolfSSL can incorrectly reject otherwise valid certificates that do not contain a Subject Alternative Name (SAN) extension. An attacker who supplies a crafted Certificate Authority certificate may trigger excessive validation failures and cause a denial of service for affected wolfSSL-based TLS clients.
A certificate validation flaw in wolfSSL can incorrectly reject otherwise valid certificates that do not contain a Subject Alternative Name (SAN) extension. An attacker who supplies a crafted Certificate Authority certificate may trigger excessive validation failures and cause a denial of service for affected wolfSSL-based TLS clients.
Affected context
The issue occurs in wolfSSL's ConfirmNameConstraints() processing within the ASN.1 certificate handling code. It is relevant to wolfSSL-based TLS clients that process attacker-controlled or untrusted Certificate Authority certificates and apply name-constraint validation to certificates without a SAN extension. The described affected releases are wolfSSL 5.9.1 and 5.9.2.
The issue occurs in wolfSSL's ConfirmNameConstraints() processing within the ASN.1 certificate handling code. It is relevant to wolfSSL-based TLS clients that process attacker-controlled or untrusted Certificate Authority certificates and apply name-constraint validation to certificates without a SAN extension. The described affected releases are wolfSSL 5.9.1 and 5.9.2.
Exploit preconditions
- Attack surface: TLS certificate processing in a wolfSSL-based client
- Required access: Ability to present or influence a crafted Certificate Authority certificate during certificate validation
- Trigger point: Name-constraint checking in
ConfirmNameConstraints() - Why exploitation is possible: Certificate validation logic can mishandle certificates lacking SAN information, causing valid certificates to be rejected and TLS operations to fail
- Attack surface: TLS certificate processing in a wolfSSL-based client
- Required access: Ability to present or influence a crafted Certificate Authority certificate during certificate validation
- Trigger point: Name-constraint checking in
ConfirmNameConstraints() - Why exploitation is possible: Certificate validation logic can mishandle certificates lacking SAN information, causing valid certificates to be rejected and TLS operations to fail
Why this happens
The underlying bug is an incorrect certificate-validation assumption in name-constraint processing. The validation path does not correctly handle the relationship between name constraints and certificates that lack a Subject Alternative Name extension, resulting in an invalid rejection decision. This maps to CWE-295: Improper Certificate Validation, where certificate attributes or validation rules are interpreted incorrectly.
The underlying bug is an incorrect certificate-validation assumption in name-constraint processing. The validation path does not correctly handle the relationship between name constraints and certificates that lack a Subject Alternative Name extension, resulting in an invalid rejection decision. This maps to CWE-295: Improper Certificate Validation, where certificate attributes or validation rules are interpreted incorrectly.
Potential impact
- TLS clients may reject otherwise valid certificates
- Applications may experience connection failures or service disruption
- Automated certificate-based workflows could become unavailable
- Attackers may cause denial of service by supplying specially crafted certificate chains
- TLS clients may reject otherwise valid certificates
- Applications may experience connection failures or service disruption
- Automated certificate-based workflows could become unavailable
- Attackers may cause denial of service by supplying specially crafted certificate chains
General mitigation guidance
Mitigation generally focuses on correcting certificate-validation behavior and reducing the effect of malformed or unexpected certificate inputs.
Common defensive patterns include:
- Applying a maintained wolfSSL release that contains the relevant validation correction
- Handling absent SAN extensions according to the applicable certificate-validation policy
- Separating certificate parsing errors from application availability decisions where practical
- Restricting accepted trust anchors and certificate-chain sources
- Using bounded, fail-safe validation paths that avoid resource exhaustion or repeated connection failures
- Monitoring certificate failures and applying least privilege to affected client processes
Mitigation generally focuses on correcting certificate-validation behavior and reducing the effect of malformed or unexpected certificate inputs.
Common defensive patterns include:
- Applying a maintained wolfSSL release that contains the relevant validation correction
- Handling absent SAN extensions according to the applicable certificate-validation policy
- Separating certificate parsing errors from application availability decisions where practical
- Restricting accepted trust anchors and certificate-chain sources
- Using bounded, fail-safe validation paths that avoid resource exhaustion or repeated connection failures
- Monitoring certificate failures and applying least privilege to affected client processes
How teams detect issues like this
Organizations can look for this issue through:
- Static and semantic analysis of X.509 name-constraint handling
- Code review checks for assumptions that every certificate contains SAN data
- Regression tests covering valid certificates with absent SAN extensions
- Fuzzing certificate chains and ASN.1 structures supplied to TLS clients
- Runtime monitoring for repeated certificate-validation failures from the same source
- Policy enforcement requiring tested certificate profiles and controlled trust-anchor distribution
Organizations can look for this issue through:
- Static and semantic analysis of X.509 name-constraint handling
- Code review checks for assumptions that every certificate contains SAN data
- Regression tests covering valid certificates with absent SAN extensions
- Fuzzing certificate chains and ASN.1 structures supplied to TLS clients
- Runtime monitoring for repeated certificate-validation failures from the same source
- Policy enforcement requiring tested certificate profiles and controlled trust-anchor distribution
Sources
| Source | Link |
|---|---|
| wolfssl. | wolfssl.com |
| gist. | gist.github.com/ |
