OCPBUGS-45290: Reject All CA-Signed Certs Using SHA1

Previously, only SHA1 leaf certs were rejected. However, in 4.16, any
SHA1 cert that is CA-signed (not self-signed) is unsupported. This led
to cases were routes with SHA1 intermediate CA certs were accepted, but
HAProxy rejects them. Self-signed SHA1 certificates (i.e. root CA)
remain supported since they are not subject to verification.

This update ensures all route certs, including the server, CA, and
destination CA certs, are inspected, and any SHA1 cert that is not
self-signed is rejected.

pkg/router/routeapihelpers/validation.go

@@ -205,6 +205,11 @@ func ExtendedValidateRoute(route *routev1.Route) field.ErrorList {
 			} else {
 				tlsConfig.CACertificate = string(data)
 			}
+			// HAProxy will fail to start if intermediate CA certs use unsupported signature algorithms.
+			// However, root CAs can still use unsupported algorithms since they are self-signed.
+			if err := validateCertSignatureAlgorithms(certs); err != nil {
+				result = append(result, field.Invalid(tlsFieldPath.Child("caCertificate"), "redacted ca certificate data", err.Error()))
+			}
 		}
 
 		verifyOptions = &x509.VerifyOptions{
@@ -254,7 +259,7 @@ func ExtendedValidateRoute(route *routev1.Route) field.ErrorList {
 	}
 
 	if len(tlsConfig.DestinationCACertificate) > 0 {
-		if _, err := cert.ParseCertsPEM([]byte(tlsConfig.DestinationCACertificate)); err != nil {
+		if certs, err := cert.ParseCertsPEM([]byte(tlsConfig.DestinationCACertificate)); err != nil {
 			errmsg := fmt.Sprintf("failed to parse destination CA certificate: %v", err)
 			result = append(result, field.Invalid(tlsFieldPath.Child("destinationCACertificate"), "redacted destination ca certificate data", errmsg))
 		} else {
@@ -263,6 +268,11 @@ func ExtendedValidateRoute(route *routev1.Route) field.ErrorList {
 			} else {
 				tlsConfig.DestinationCACertificate = string(data)
 			}
+			// Unsupported destinationCACertificates algorithms won't prevent HAProxy from starting.
+			// However, HAProxy will quietly refuse to use them at runtime. Rejecting here improves UX.
+			if err := validateCertSignatureAlgorithms(certs); err != nil {
+				result = append(result, field.Invalid(tlsFieldPath.Child("destinationCACertificate"), "redacted ca certificate data", err.Error()))
+			}
 		}
 	}
 
@@ -353,6 +363,35 @@ func validateInsecureEdgeTerminationPolicy(tls *routev1.TLSConfig, fldPath *fiel
 	return nil
 }
 
+// isSelfSignedCert determines if a provided certificate is self-signed.
+func isSelfSignedCert(cert *x509.Certificate) bool {
+	// Verify the certificate's signature using its own public key.
+	err := cert.CheckSignature(cert.SignatureAlgorithm, cert.RawTBSCertificate, cert.Signature)
+	return err == nil
+}
+
+// validateCertSignatureAlgorithms checks if the certificate list has any certs that use a
+// signature algorithm that the router no longer supports. If an unsupported cert is present, HAProxy
+// may refuse to start (server & CA certs) or may start but reject connections (destination CA certs).
+func validateCertSignatureAlgorithms(certs []*x509.Certificate) error {
+	for _, cert := range certs {
+		// Verify the signature algorithms only for certs signed by a CA.
+		// Self-signed certificates are not subject to validation, so their signature algorithm is not used.
+		// It's important that we do NOT reject self-signed certificates, as many root CAs still utilize SHA1.
+		if !isSelfSignedCert(cert) {
+			switch certs[0].SignatureAlgorithm {
+			case x509.SHA1WithRSA, x509.ECDSAWithSHA1:
+				return fmt.Errorf("router does not support CA-signed certs using SHA1")
+			case x509.MD5WithRSA:
+				return fmt.Errorf("router does not support CA-signed certs using MD5")
+			default:
+				// Acceptable algorithm
+			}
+		}
+	}
+	return nil
+}
+
 // validateCertificatePEM checks if a certificate PEM is valid and
 // optionally verifies the certificate using the options.
 func validateCertificatePEM(certPEM string, options *x509.VerifyOptions) ([]*x509.Certificate, error) {
@@ -366,13 +405,8 @@ func validateCertificatePEM(certPEM string, options *x509.VerifyOptions) ([]*x50
 	}
 
 	// Reject any unsupported cert algorithms as HaProxy will refuse to start with them.
-	switch certs[0].SignatureAlgorithm {
-	case x509.SHA1WithRSA, x509.ECDSAWithSHA1:
-		return certs, fmt.Errorf("router does not support certs using SHA1")
-	case x509.MD5WithRSA:
-		return certs, fmt.Errorf("router does not support certs using MD5")
-	default:
-		// Acceptable algorithm
+	if err := validateCertSignatureAlgorithms(certs); err != nil {
+		return certs, err
 	}
 
 	if options != nil {