Fehlerhafte Zertifikatsignaturprüfung bei X.509-Kettenvalidierung ermöglicht gefälschte Blattzertifikate

The impact of CVE-2026-5501 is significant. An attacker who can obtain a legitimate leaf certificate from a trusted Certificate Authority (CA), such as a free DV certificate from Let's Encrypt, can forge a certificate for any subject name and with any public key. This is achieved by supplying a legitimately signed, but untrusted, intermediate certificate with CA:FALSE in its Basic Constraints extension. The wolfSSLX509verify_cert function will incorrectly return success, allowing the forged certificate to be accepted. This enables man-in-the-middle (MITM) attacks, allowing an attacker to intercept and decrypt sensitive communications. The ability to forge certificates effectively compromises the entire trust chain, enabling unauthorized access to systems and data. This vulnerability is particularly concerning because it leverages existing trust relationships, making detection more difficult.

Systems utilizing wolfSSL versions 0.0.0 through 5.9.0 are at risk, particularly those relying on the OpenSSL compatibility layer for certificate validation. This includes applications and services that handle sensitive data over TLS, such as web servers, API gateways, and VPN servers. Shared hosting environments using vulnerable wolfSSL versions are also at increased risk due to the potential for cross-tenant attacks.

• nginx: Examine Nginx error logs for unusual certificate validation failures or errors related to certificate chain construction. Use nginx -t to validate configuration after any changes.

grep -i "certificate validation failed" /var/log/nginx/error.log

• generic web: Monitor web server access logs for connections using certificates with unexpected or suspicious subject names. Use curl to test certificate validation.

curl -v https://your-website.com --dump-header - | grep Subject:

• database (mysql, redis, mongodb, postgresql): While the vulnerability is in wolfSSL, if your database uses wolfSSL for TLS, monitor database connection logs for unusual certificate fingerprints or validation errors. This is less direct but can indicate a compromised connection. • linux / server: Monitor system logs for unusual TLS connection attempts or errors related to certificate validation. Use journalctl to filter for relevant events.

journalctl -u nginx -g "certificate validation failed"

1. 2026-04-10Disclosure

   disclosure

2. 2026-04-10Patch

   patch

1. Reserviert2026-04-03
2. Veröffentlicht2026-04-10
3. Geändert2026-04-22
4. EPSS aktualisiert2026-04-17

The primary mitigation for CVE-2026-5501 is to upgrade to wolfSSL version 5.11.0 or later, which contains the fix. If upgrading immediately is not possible, consider implementing temporary workarounds. While a direct workaround isn't available within wolfSSL itself, stricter certificate validation policies can be enforced at the application level. This might involve verifying the certificate chain's validity against a known list of trusted CAs or implementing stricter checks on certificate extensions. For environments using Nginx, review and potentially tighten TLS configuration settings to minimize the impact of potentially forged certificates. After upgrading, confirm the fix by attempting to present a forged certificate to the application and verifying that the verification process fails.