Partial-chain certificate verification flaw in wolfSSL

Compliance Impact

This vulnerability allows acceptance of certificate chains that terminate at an untrusted intermediate certificate controlled by an attacker, rather than a trusted anchor. Such improper validation can lead to unauthorized access or interception of sensitive data.

Because standards and regulations like GDPR and HIPAA require strong protections for data confidentiality and integrity, this vulnerability could undermine compliance by enabling attackers to bypass certificate validation mechanisms, potentially exposing protected data.

The fix implemented ensures stricter validation of certificate chains, preventing acceptance of untrusted or incomplete chains, thereby helping maintain compliance with security requirements mandated by these regulations.

Useful 0 Not Useful 0

Executive Summary

This vulnerability involves partial-chain certificate verification in certain OpenSSL compatibility paths within wolfSSL. When the X509_V_FLAG_PARTIAL_CHAIN verify flag is enabled, the verification process may incorrectly accept certificate chains that end at an untrusted intermediate certificate supplied by a peer, instead of requiring the chain to terminate at a trusted root certificate authority. An attacker could exploit this by presenting a certificate chain that ends at an intermediate certificate they control, causing the system to accept it as valid.

Useful 0 Not Useful 0

Impact Analysis

The impact of this vulnerability is that an attacker could present a malicious certificate chain that appears valid due to the acceptance of an untrusted intermediate certificate. This could lead to man-in-the-middle attacks, unauthorized access, or impersonation of trusted entities, potentially compromising secure communications or authentication processes that rely on certificate validation.

Useful 0 Not Useful 0

Detection Guidance

Detection of this vulnerability involves verifying whether the wolfSSL library in use improperly accepts partial certificate chains that terminate at an untrusted intermediate certificate. Since the issue relates to the X509_V_FLAG_PARTIAL_CHAIN flag handling in certificate verification, detection requires checking certificate validation behavior.

One approach is to test certificate chain verification using wolfSSL tools or custom code that exercises the wolfSSL_X509_verify_cert function with the X509_V_FLAG_PARTIAL_CHAIN flag enabled. You can attempt to validate a certificate chain that ends at an attacker-controlled intermediate certificate and observe if it is incorrectly accepted.

Specific commands are not provided in the resources, but you may consider running wolfSSL test suites or custom scripts that replicate the partial chain verification scenario, or use debugging/logging to monitor certificate verification results in your environment.

Useful 0 Not Useful 0

Mitigation Strategies

To mitigate this vulnerability, update the wolfSSL library to a version that includes the fix from pull request #10170. This fix ensures that partial chain verification only succeeds if the terminal certificate is trusted by the original trust set, preventing acceptance of untrusted intermediate certificates.

If updating immediately is not possible, consider disabling the use of the X509_V_FLAG_PARTIAL_CHAIN flag in your certificate verification configuration to avoid relying on partial chain verification that may be vulnerable.

Additionally, review your certificate trust settings to ensure that only trusted anchors are accepted and monitor certificate validation logs for suspicious acceptance of untrusted intermediates.

Useful 0 Not Useful 0