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-rw-r--r--libsylph/ssl_hostname_validation.c163
1 files changed, 163 insertions, 0 deletions
diff --git a/libsylph/ssl_hostname_validation.c b/libsylph/ssl_hostname_validation.c
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+/*
+ * Helper functions to perform basic hostname validation using OpenSSL.
+ *
+ * Copyright (C) 2012, iSEC Partners.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ + use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+ * of the Software, and to permit persons to whom the Software is furnished to do
+ + so, subject to the following conditions:
+ +
+ + The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ * Author: Alban Diquet
+ *
+ * https://github.com/iSECPartners/ssl-conservatory
+ *
+ * Modified naming convention to match LibSylph.
+ *
+ */
+
+
+#include <strings.h>
+#include <openssl/x509v3.h>
+#include <openssl/ssl.h>
+
+#include "ssl_hostname_validation.h"
+
+
+#define HOSTNAME_MAX_SIZE 255
+
+/**
+* Tries to find a match for hostname in the certificate's Common Name field.
+*
+* Returns MatchFound if a match was found.
+* Returns MatchNotFound if no matches were found.
+* Returns MalformedCertificate if the Common Name had a NUL character embedded in it.
+* Returns Error if the Common Name could not be extracted.
+*/
+static SSLHostnameValidationResult matches_common_name(const char *hostname, const X509 *server_cert) {
+ int common_name_loc = -1;
+ X509_NAME_ENTRY *common_name_entry = NULL;
+ ASN1_STRING *common_name_asn1 = NULL;
+ char *common_name_str = NULL;
+
+ // Find the position of the CN field in the Subject field of the certificate
+ common_name_loc = X509_NAME_get_index_by_NID(X509_get_subject_name((X509 *) server_cert), NID_commonName, -1);
+ if (common_name_loc < 0) {
+ return SSL_HOSTNAME_ERROR;
+ }
+
+ // Extract the CN field
+ common_name_entry = X509_NAME_get_entry(X509_get_subject_name((X509 *) server_cert), common_name_loc);
+ if (common_name_entry == NULL) {
+ return SSL_HOSTNAME_ERROR;
+ }
+
+ // Convert the CN field to a C string
+ common_name_asn1 = X509_NAME_ENTRY_get_data(common_name_entry);
+ if (common_name_asn1 == NULL) {
+ return SSL_HOSTNAME_ERROR;
+ }
+ common_name_str = (char *) ASN1_STRING_data(common_name_asn1);
+
+ // Make sure there isn't an embedded NUL character in the CN
+ if (ASN1_STRING_length(common_name_asn1) != strlen(common_name_str)) {
+ return SSL_HOSTNAME_MALFORMED_CERTIFICATE;
+ }
+
+ // Compare expected hostname with the CN
+ if (strcasecmp(hostname, common_name_str) == 0) {
+ return SSL_HOSTNAME_MATCH_FOUND;
+ }
+ else {
+ return SSL_HOSTNAME_MATCH_NOT_FOUND;
+ }
+}
+
+
+/**
+* Tries to find a match for hostname in the certificate's Subject Alternative Name extension.
+*
+* Returns MatchFound if a match was found.
+* Returns MatchNotFound if no matches were found.
+* Returns MalformedCertificate if any of the hostnames had a NUL character embedded in it.
+* Returns NoSANPresent if the SAN extension was not present in the certificate.
+*/
+static SSLHostnameValidationResult matches_subject_alternative_name(const char *hostname, const X509 *server_cert) {
+ SSLHostnameValidationResult result = SSL_HOSTNAME_MATCH_NOT_FOUND;
+ int i;
+ int san_names_nb = -1;
+ STACK_OF(GENERAL_NAME) *san_names = NULL;
+
+ // Try to extract the names within the SAN extension from the certificate
+ san_names = X509_get_ext_d2i((X509 *) server_cert, NID_subject_alt_name, NULL, NULL);
+ if (san_names == NULL) {
+ return SSL_HOSTNAME_NO_SAN_PRESENT;
+ }
+ san_names_nb = sk_GENERAL_NAME_num(san_names);
+
+ // Check each name within the extension
+ for (i=0; i<san_names_nb; i++) {
+ const GENERAL_NAME *current_name = sk_GENERAL_NAME_value(san_names, i);
+
+ if (current_name->type == GEN_DNS) {
+ // Current name is a DNS name, let's check it
+ char *dns_name = (char *) ASN1_STRING_data(current_name->d.dNSName);
+
+ // Make sure there isn't an embedded NUL character in the DNS name
+ if (ASN1_STRING_length(current_name->d.dNSName) != strlen(dns_name)) {
+ result = SSL_HOSTNAME_MALFORMED_CERTIFICATE;
+ break;
+ }
+ else { // Compare expected hostname with the DNS name
+ if (strcasecmp(hostname, dns_name) == 0) {
+ result = SSL_HOSTNAME_MATCH_FOUND;
+ break;
+ }
+ }
+ }
+ }
+ sk_GENERAL_NAME_pop_free(san_names, GENERAL_NAME_free);
+
+ return result;
+}
+
+
+/**
+* Validates the server's identity by looking for the expected hostname in the
+* server's certificate. As described in RFC 6125, it first tries to find a match
+* in the Subject Alternative Name extension. If the extension is not present in
+* the certificate, it checks the Common Name instead.
+*
+* Returns MatchFound if a match was found.
+* Returns MatchNotFound if no matches were found.
+* Returns MalformedCertificate if any of the hostnames had a NUL character embedded in it.
+* Returns Error if there was an error.
+*/
+SSLHostnameValidationResult ssl_validate_hostname(const char *hostname, const X509 *server_cert) {
+ SSLHostnameValidationResult result;
+
+ if((hostname == NULL) || (server_cert == NULL))
+ return SSL_HOSTNAME_ERROR;
+
+ // First try the Subject Alternative Names extension
+ result = matches_subject_alternative_name(hostname, server_cert);
+ if (result == SSL_HOSTNAME_NO_SAN_PRESENT) {
+ // Extension was not found: try the Common Name
+ result = matches_common_name(hostname, server_cert);
+ }
+
+ return result;
+}