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 */
matches_common_name(const char * hostname,const X509 * server_cert)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 */
matches_subject_alternative_name(const char * hostname,const X509 * server_cert)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 */
validate_hostname(const char * hostname,const X509 * server_cert)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