1 /* Obtained from: https://github.com/iSECPartners/ssl-conservatory */ 2 3 /* 4 Copyright (C) 2012, iSEC Partners. 5 6 Permission is hereby granted, free of charge, to any person obtaining a copy of 7 this software and associated documentation files (the "Software"), to deal in 8 the Software without restriction, including without limitation the rights to 9 use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies 10 of the Software, and to permit persons to whom the Software is furnished to do 11 so, subject to the following conditions: 12 13 The above copyright notice and this permission notice shall be included in all 14 copies or substantial portions of the Software. 15 16 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 17 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 18 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 19 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 20 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 21 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 22 SOFTWARE. 23 */ 24 25 /* 26 * Helper functions to perform basic hostname validation using OpenSSL. 27 * 28 * Please read "everything-you-wanted-to-know-about-openssl.pdf" before 29 * attempting to use this code. This whitepaper describes how the code works, 30 * how it should be used, and what its limitations are. 31 * 32 * Author: Alban Diquet 33 * License: See LICENSE 34 * 35 */ 36 37 // Get rid of OSX 10.7 and greater deprecation warnings. 38 #if defined(__APPLE__) && defined(__clang__) 39 #pragma clang diagnostic ignored "-Wdeprecated-declarations" 40 #endif 41 42 #include <openssl/x509v3.h> 43 #include <openssl/ssl.h> 44 45 #include "openssl_hostname_validation.h" 46 #include "hostcheck.h" 47 48 #define HOSTNAME_MAX_SIZE 255 49 50 /** 51 * Tries to find a match for hostname in the certificate's Common Name field. 52 * 53 * Returns MatchFound if a match was found. 54 * Returns MatchNotFound if no matches were found. 55 * Returns MalformedCertificate if the Common Name had a NUL character embedded in it. 56 * Returns Error if the Common Name could not be extracted. 57 */ 58 static HostnameValidationResult matches_common_name(const char *hostname, const X509 *server_cert) { 59 int common_name_loc = -1; 60 X509_NAME_ENTRY *common_name_entry = NULL; 61 ASN1_STRING *common_name_asn1 = NULL; 62 char *common_name_str = NULL; 63 64 // Find the position of the CN field in the Subject field of the certificate 65 common_name_loc = X509_NAME_get_index_by_NID(X509_get_subject_name((X509 *) server_cert), NID_commonName, -1); 66 if (common_name_loc < 0) { 67 return Error; 68 } 69 70 // Extract the CN field 71 common_name_entry = X509_NAME_get_entry(X509_get_subject_name((X509 *) server_cert), common_name_loc); 72 if (common_name_entry == NULL) { 73 return Error; 74 } 75 76 // Convert the CN field to a C string 77 common_name_asn1 = X509_NAME_ENTRY_get_data(common_name_entry); 78 if (common_name_asn1 == NULL) { 79 return Error; 80 } 81 common_name_str = (char *) ASN1_STRING_data(common_name_asn1); 82 83 // Make sure there isn't an embedded NUL character in the CN 84 if ((size_t)ASN1_STRING_length(common_name_asn1) != strlen(common_name_str)) { 85 return MalformedCertificate; 86 } 87 88 // Compare expected hostname with the CN 89 if (Curl_cert_hostcheck(common_name_str, hostname) == CURL_HOST_MATCH) { 90 return MatchFound; 91 } 92 else { 93 return MatchNotFound; 94 } 95 } 96 97 98 /** 99 * Tries to find a match for hostname in the certificate's Subject Alternative Name extension. 100 * 101 * Returns MatchFound if a match was found. 102 * Returns MatchNotFound if no matches were found. 103 * Returns MalformedCertificate if any of the hostnames had a NUL character embedded in it. 104 * Returns NoSANPresent if the SAN extension was not present in the certificate. 105 */ 106 static HostnameValidationResult matches_subject_alternative_name(const char *hostname, const X509 *server_cert) { 107 HostnameValidationResult result = MatchNotFound; 108 int i; 109 int san_names_nb = -1; 110 STACK_OF(GENERAL_NAME) *san_names = NULL; 111 112 // Try to extract the names within the SAN extension from the certificate 113 san_names = X509_get_ext_d2i((X509 *) server_cert, NID_subject_alt_name, NULL, NULL); 114 if (san_names == NULL) { 115 return NoSANPresent; 116 } 117 san_names_nb = sk_GENERAL_NAME_num(san_names); 118 119 // Check each name within the extension 120 for (i=0; i<san_names_nb; i++) { 121 const GENERAL_NAME *current_name = sk_GENERAL_NAME_value(san_names, i); 122 123 if (current_name->type == GEN_DNS) { 124 // Current name is a DNS name, let's check it 125 char *dns_name = (char *) ASN1_STRING_data(current_name->d.dNSName); 126 127 // Make sure there isn't an embedded NUL character in the DNS name 128 if ((size_t)ASN1_STRING_length(current_name->d.dNSName) != strlen(dns_name)) { 129 result = MalformedCertificate; 130 break; 131 } 132 else { // Compare expected hostname with the DNS name 133 if (Curl_cert_hostcheck(dns_name, hostname) 134 == CURL_HOST_MATCH) { 135 result = MatchFound; 136 break; 137 } 138 } 139 } 140 } 141 sk_GENERAL_NAME_pop_free(san_names, GENERAL_NAME_free); 142 143 return result; 144 } 145 146 147 /** 148 * Validates the server's identity by looking for the expected hostname in the 149 * server's certificate. As described in RFC 6125, it first tries to find a match 150 * in the Subject Alternative Name extension. If the extension is not present in 151 * the certificate, it checks the Common Name instead. 152 * 153 * Returns MatchFound if a match was found. 154 * Returns MatchNotFound if no matches were found. 155 * Returns MalformedCertificate if any of the hostnames had a NUL character embedded in it. 156 * Returns Error if there was an error. 157 */ 158 HostnameValidationResult validate_hostname(const char *hostname, const X509 *server_cert) { 159 HostnameValidationResult result; 160 161 if((hostname == NULL) || (server_cert == NULL)) 162 return Error; 163 164 // First try the Subject Alternative Names extension 165 result = matches_subject_alternative_name(hostname, server_cert); 166 if (result == NoSANPresent) { 167 // Extension was not found: try the Common Name 168 result = matches_common_name(hostname, server_cert); 169 } 170 171 return result; 172 } 173