CVE-2026-5501: Improper Certificate Signature Verification in X.509 Chain Validation Allows Forged Leaf Certificates
wolfSSLX509verifycert in the OpenSSL compatibility layer accepts a certificate chain in which the leaf's signature is not checked, if the attacker supplies an untrusted intermediate with Basic Constraints CA:FALSE that is legitimately signed by a trusted root. An attacker who obtains any leaf certificate from a trusted CA (e.g. a free DV cert from Let's Encrypt) can forge a certificate for any subject name with any public key and arbitrary signature bytes, and the function returns WOLFSSLSUCCESS / X509VOK. The native wolfSSL TLS handshake path (ProcessPeerCerts) is not susceptible and the issue is limited to applications using the OpenSSL compatibility API directly, which would include integrations of wolfSSL into nginx and haproxy.
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-5501?
CVE-2026-5501 is classified as a high severity vulnerability due to its potential to allow forged leaf certificates.
How do I fix CVE-2026-5501?
To fix CVE-2026-5501, update to the latest version of wolfSSL that addresses the improper certificate signature verification issue.
What systems are affected by CVE-2026-5501?
CVE-2026-5501 primarily affects wolfSSL implementations that utilize the OpenSSL compatibility layer.
What is the impact of CVE-2026-5501?
The impact of CVE-2026-5501 is that it allows attackers to exploit improper signature verification and potentially execute man-in-the-middle attacks.
How does CVE-2026-5501 occur?
CVE-2026-5501 occurs when wolfSSL_X509_verify_cert does not check the signature of a leaf certificate that depends on an untrusted intermediate certificate.