CVE-2025-4947: QUIC certificate check skip with wolfSSL

How it was found

Summary:

When using WolfSSL as the TLS backend, there is an issue where the CN or SAN in the certificate is not verified when connecting to an IP address over HTTP/3.

wolfSSL_X509_check_host is only called when peer->sni is not NULL. However, when an IP address is specified, peer->sni is NULL, so the verification does not occur.

Curl_vquic_tls_verify_peer()

#elif defined(USE_WOLFSSL)
  (void)data;
  if(conn_config->verifyhost) {
    if(peer->sni) {
      WOLFSSL_X509* cert = wolfSSL_get_peer_certificate(ctx->wssl.ssl);
      if(wolfSSL_X509_check_host(cert, peer->sni, strlen(peer->sni), 0, NULL)
            == WOLFSSL_FAILURE) {
        result = CURLE_PEER_FAILED_VERIFICATION;
      }
      wolfSSL_X509_free(cert);
    }

  }
#endif

Affected version

curl -V
WARNING: this libcurl is Debug-enabled, do not use in production

curl 8.13.0 (x86_64-pc-linux-gnu) libcurl/8.13.0 wolfSSL/5.8.0 zlib/1.3.1 libidn2/2.3.8 libpsl/0.21.2 ngtcp2/1.13.0-DEV nghttp3/1.1
Release-Date: 2025-04-02
Protocols: dict file ftp ftps gopher gophers http https imap imaps ipfs ipns mqtt pop3 pop3s rtsp smtp smtps telnet tftp ws wss
Features: alt-svc AsynchDNS Debug HSTS HTTP3 HTTPS-proxy IDN IPv6 Largefile libz PSL SSL threadsafe TrackMemory UnixSockets

Steps To Reproduce:

I will explain using a connection to google.com as an example.

1. Prepare curl with WolfSSL backend.
2. To resolve the domain name google.com and obtain its IP address for testing purposes(142.251.222.14).
3. curl --http3 https://142.251.222.14

When an IP address is specified, it should result in an error during CN/SAN verification, but no error occurs. An error occurs when using HTTP/1.1.

An error occurs when the TLS backend is OpenSSL.

Impact

CWE-297: Improper Validation of Certificate with Host Mismatch