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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;
}
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