CVE-2026-5501— Improper Certificate Signature Verification in X.509 Chain Validation Allows Forged Leaf Certificates

Improper Certificate Signature Verification in X.509 Chain Validation Allows Forged Leaf Certificates

wolfSSL_X509_verify_cert 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 `WOLFSSL_SUCCESS` / `X509_V_OK`. 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.

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证书验证不恰当

wolfSSL 安全漏洞

wolfSSL（CyaSSL）是美国wolfSSL公司的一个针对嵌入式系统开发人员使用的小的、可移植的嵌入式SSL编程库。 wolfSSL存在安全漏洞，该漏洞源于OpenSSL兼容层中的wolfSSL_X509_verify_cert函数在攻击者提供由受信任根合法签名但Basic Constraints为CA:FALSE的不可信中间证书时，不会检查叶子证书的签名，可能导致攻击者伪造任意主题名称和公钥的证书。

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