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 #include <string.h> 45 46 #include "openssl_hostname_validation.h" 47 #include "hostcheck.h" 48 49 #define HOSTNAME_MAX_SIZE 255 50 51 #if OPENSSL_VERSION_NUMBER < 0x10100000L 52 #define ASN1_STRING_get0_data ASN1_STRING_data 53 #endif 54 55 /** 56 * Tries to find a match for hostname in the certificate's Common Name field. 57 * 58 * Returns MatchFound if a match was found. 59 * Returns MatchNotFound if no matches were found. 60 * Returns MalformedCertificate if the Common Name had a NUL character embedded in it. 61 * Returns Error if the Common Name could not be extracted. 62 */ 63 static HostnameValidationResult matches_common_name(const char *hostname, const X509 *server_cert) { 64 int common_name_loc = -1; 65 X509_NAME_ENTRY *common_name_entry = NULL; 66 ASN1_STRING *common_name_asn1 = NULL; 67 const char *common_name_str = NULL; 68 69 // Find the position of the CN field in the Subject field of the certificate 70 common_name_loc = X509_NAME_get_index_by_NID(X509_get_subject_name((X509 *) server_cert), NID_commonName, -1); 71 if (common_name_loc < 0) { 72 return Error; 73 } 74 75 // Extract the CN field 76 common_name_entry = X509_NAME_get_entry(X509_get_subject_name((X509 *) server_cert), common_name_loc); 77 if (common_name_entry == NULL) { 78 return Error; 79 } 80 81 // Convert the CN field to a C string 82 common_name_asn1 = X509_NAME_ENTRY_get_data(common_name_entry); 83 if (common_name_asn1 == NULL) { 84 return Error; 85 } 86 common_name_str = (char *) ASN1_STRING_get0_data(common_name_asn1); 87 88 // Make sure there isn't an embedded NUL character in the CN 89 if ((size_t)ASN1_STRING_length(common_name_asn1) != strlen(common_name_str)) { 90 return MalformedCertificate; 91 } 92 93 // Compare expected hostname with the CN 94 if (Curl_cert_hostcheck(common_name_str, hostname) == CURL_HOST_MATCH) { 95 return MatchFound; 96 } 97 else { 98 return MatchNotFound; 99 } 100 } 101 102 103 /** 104 * Tries to find a match for hostname in the certificate's Subject Alternative Name extension. 105 * 106 * Returns MatchFound if a match was found. 107 * Returns MatchNotFound if no matches were found. 108 * Returns MalformedCertificate if any of the hostnames had a NUL character embedded in it. 109 * Returns NoSANPresent if the SAN extension was not present in the certificate. 110 */ 111 static HostnameValidationResult matches_subject_alternative_name(const char *hostname, const X509 *server_cert) { 112 HostnameValidationResult result = MatchNotFound; 113 int i; 114 int san_names_nb = -1; 115 STACK_OF(GENERAL_NAME) *san_names = NULL; 116 117 // Try to extract the names within the SAN extension from the certificate 118 san_names = X509_get_ext_d2i((X509 *) server_cert, NID_subject_alt_name, NULL, NULL); 119 if (san_names == NULL) { 120 return NoSANPresent; 121 } 122 san_names_nb = sk_GENERAL_NAME_num(san_names); 123 124 // Check each name within the extension 125 for (i=0; i<san_names_nb; i++) { 126 const GENERAL_NAME *current_name = sk_GENERAL_NAME_value(san_names, i); 127 128 if (current_name->type == GEN_DNS) { 129 // Current name is a DNS name, let's check it 130 const char *dns_name = (char *) ASN1_STRING_get0_data(current_name->d.dNSName); 131 132 // Make sure there isn't an embedded NUL character in the DNS name 133 if ((size_t)ASN1_STRING_length(current_name->d.dNSName) != strlen(dns_name)) { 134 result = MalformedCertificate; 135 break; 136 } 137 else { // Compare expected hostname with the DNS name 138 if (Curl_cert_hostcheck(dns_name, hostname) 139 == CURL_HOST_MATCH) { 140 result = MatchFound; 141 break; 142 } 143 } 144 } 145 } 146 sk_GENERAL_NAME_pop_free(san_names, GENERAL_NAME_free); 147 148 return result; 149 } 150 151 152 /** 153 * Validates the server's identity by looking for the expected hostname in the 154 * server's certificate. As described in RFC 6125, it first tries to find a match 155 * in the Subject Alternative Name extension. If the extension is not present in 156 * the certificate, it checks the Common Name instead. 157 * 158 * Returns MatchFound if a match was found. 159 * Returns MatchNotFound if no matches were found. 160 * Returns MalformedCertificate if any of the hostnames had a NUL character embedded in it. 161 * Returns Error if there was an error. 162 */ 163 HostnameValidationResult validate_hostname(const char *hostname, const X509 *server_cert) { 164 HostnameValidationResult result; 165 166 if((hostname == NULL) || (server_cert == NULL)) 167 return Error; 168 169 // First try the Subject Alternative Names extension 170 result = matches_subject_alternative_name(hostname, server_cert); 171 if (result == NoSANPresent) { 172 // Extension was not found: try the Common Name 173 result = matches_common_name(hostname, server_cert); 174 } 175 176 return result; 177 } 178