1 /* $OpenBSD: tls_verify.c,v 1.28 2023/06/01 07:32:25 tb Exp $ */ 2 /* 3 * Copyright (c) 2014 Jeremie Courreges-Anglas <jca@openbsd.org> 4 * 5 * Permission to use, copy, modify, and distribute this software for any 6 * purpose with or without fee is hereby granted, provided that the above 7 * copyright notice and this permission notice appear in all copies. 8 * 9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16 */ 17 18 #include <sys/socket.h> 19 20 #include <arpa/inet.h> 21 #include <netinet/in.h> 22 23 #include <string.h> 24 25 #include <openssl/x509v3.h> 26 27 #include <tls.h> 28 #include "tls_internal.h" 29 30 static int 31 tls_match_name(const char *cert_name, const char *name) 32 { 33 const char *cert_domain, *domain, *next_dot; 34 35 if (strcasecmp(cert_name, name) == 0) 36 return 0; 37 38 /* Wildcard match? */ 39 if (cert_name[0] == '*') { 40 /* 41 * Valid wildcards: 42 * - "*.domain.tld" 43 * - "*.sub.domain.tld" 44 * - etc. 45 * Reject "*.tld". 46 * No attempt to prevent the use of eg. "*.co.uk". 47 */ 48 cert_domain = &cert_name[1]; 49 /* Disallow "*" */ 50 if (cert_domain[0] == '\0') 51 return -1; 52 /* Disallow "*foo" */ 53 if (cert_domain[0] != '.') 54 return -1; 55 /* Disallow "*.." */ 56 if (cert_domain[1] == '.') 57 return -1; 58 next_dot = strchr(&cert_domain[1], '.'); 59 /* Disallow "*.bar" */ 60 if (next_dot == NULL) 61 return -1; 62 /* Disallow "*.bar.." */ 63 if (next_dot[1] == '.') 64 return -1; 65 66 domain = strchr(name, '.'); 67 68 /* No wildcard match against a name with no host part. */ 69 if (name[0] == '.') 70 return -1; 71 /* No wildcard match against a name with no domain part. */ 72 if (domain == NULL || strlen(domain) == 1) 73 return -1; 74 75 if (strcasecmp(cert_domain, domain) == 0) 76 return 0; 77 } 78 79 return -1; 80 } 81 82 /* 83 * See RFC 5280 section 4.2.1.6 for SubjectAltName details. 84 * alt_match is set to 1 if a matching alternate name is found. 85 * alt_exists is set to 1 if any known alternate name exists in the certificate. 86 */ 87 static int 88 tls_check_subject_altname(struct tls *ctx, X509 *cert, const char *name, 89 int *alt_match, int *alt_exists) 90 { 91 STACK_OF(GENERAL_NAME) *altname_stack = NULL; 92 union tls_addr addrbuf; 93 int addrlen, type; 94 int count, i; 95 int critical = 0; 96 int rv = -1; 97 98 *alt_match = 0; 99 *alt_exists = 0; 100 101 altname_stack = X509_get_ext_d2i(cert, NID_subject_alt_name, &critical, 102 NULL); 103 if (altname_stack == NULL) { 104 if (critical != -1) { 105 tls_set_errorx(ctx, "error decoding subjectAltName"); 106 goto err; 107 } 108 goto done; 109 } 110 111 if (inet_pton(AF_INET, name, &addrbuf) == 1) { 112 type = GEN_IPADD; 113 addrlen = 4; 114 } else if (inet_pton(AF_INET6, name, &addrbuf) == 1) { 115 type = GEN_IPADD; 116 addrlen = 16; 117 } else { 118 type = GEN_DNS; 119 addrlen = 0; 120 } 121 122 count = sk_GENERAL_NAME_num(altname_stack); 123 for (i = 0; i < count; i++) { 124 GENERAL_NAME *altname; 125 126 altname = sk_GENERAL_NAME_value(altname_stack, i); 127 128 if (altname->type == GEN_DNS || altname->type == GEN_IPADD) 129 *alt_exists = 1; 130 131 if (altname->type != type) 132 continue; 133 134 if (type == GEN_DNS) { 135 const unsigned char *data; 136 int format, len; 137 138 format = ASN1_STRING_type(altname->d.dNSName); 139 if (format == V_ASN1_IA5STRING) { 140 data = ASN1_STRING_get0_data(altname->d.dNSName); 141 len = ASN1_STRING_length(altname->d.dNSName); 142 143 if (len < 0 || (size_t)len != strlen(data)) { 144 tls_set_errorx(ctx, 145 "error verifying name '%s': " 146 "NUL byte in subjectAltName, " 147 "probably a malicious certificate", 148 name); 149 goto err; 150 } 151 152 /* 153 * Per RFC 5280 section 4.2.1.6: 154 * " " is a legal domain name, but that 155 * dNSName must be rejected. 156 */ 157 if (strcmp(data, " ") == 0) { 158 tls_set_errorx(ctx, 159 "error verifying name '%s': " 160 "a dNSName of \" \" must not be " 161 "used", name); 162 goto err; 163 } 164 165 if (tls_match_name(data, name) == 0) { 166 *alt_match = 1; 167 goto done; 168 } 169 } else { 170 #ifdef DEBUG 171 fprintf(stdout, "%s: unhandled subjectAltName " 172 "dNSName encoding (%d)\n", getprogname(), 173 format); 174 #endif 175 } 176 177 } else if (type == GEN_IPADD) { 178 const unsigned char *data; 179 int datalen; 180 181 datalen = ASN1_STRING_length(altname->d.iPAddress); 182 data = ASN1_STRING_get0_data(altname->d.iPAddress); 183 184 if (datalen < 0) { 185 tls_set_errorx(ctx, 186 "Unexpected negative length for an " 187 "IP address: %d", datalen); 188 goto err; 189 } 190 191 /* 192 * Per RFC 5280 section 4.2.1.6: 193 * IPv4 must use 4 octets and IPv6 must use 16 octets. 194 */ 195 if (datalen == addrlen && 196 memcmp(data, &addrbuf, addrlen) == 0) { 197 *alt_match = 1; 198 goto done; 199 } 200 } 201 } 202 203 done: 204 rv = 0; 205 206 err: 207 sk_GENERAL_NAME_pop_free(altname_stack, GENERAL_NAME_free); 208 return rv; 209 } 210 211 static int 212 tls_check_common_name(struct tls *ctx, X509 *cert, const char *name, 213 int *cn_match) 214 { 215 unsigned char *utf8_bytes = NULL; 216 X509_NAME *subject_name; 217 char *common_name = NULL; 218 union tls_addr addrbuf; 219 int common_name_len; 220 ASN1_STRING *data; 221 int lastpos = -1; 222 int rv = -1; 223 224 *cn_match = 0; 225 226 subject_name = X509_get_subject_name(cert); 227 if (subject_name == NULL) 228 goto done; 229 230 lastpos = X509_NAME_get_index_by_NID(subject_name, 231 NID_commonName, lastpos); 232 if (lastpos == -1) 233 goto done; 234 if (lastpos < 0) 235 goto err; 236 if (X509_NAME_get_index_by_NID(subject_name, NID_commonName, lastpos) 237 != -1) { 238 /* 239 * Having multiple CN's is possible, and even happened back in 240 * the glory days of mullets and Hammer pants. In anything like 241 * a modern TLS cert, CN is as close to deprecated as it gets, 242 * and having more than one is bad. We therefore fail if we have 243 * more than one CN fed to us in the subject, treating the 244 * certificate as hostile. 245 */ 246 tls_set_errorx(ctx, "error verifying name '%s': " 247 "Certificate subject contains mutiple Common Name fields, " 248 "probably a malicious or malformed certificate", name); 249 goto err; 250 } 251 252 data = X509_NAME_ENTRY_get_data(X509_NAME_get_entry(subject_name, 253 lastpos)); 254 /* 255 * Fail if we cannot encode the CN bytes as UTF-8. 256 */ 257 if ((common_name_len = ASN1_STRING_to_UTF8(&utf8_bytes, data)) < 0) { 258 tls_set_errorx(ctx, "error verifying name '%s': " 259 "Common Name field cannot be encoded as a UTF-8 string, " 260 "probably a malicious certificate", name); 261 goto err; 262 } 263 /* 264 * Fail if the CN is of invalid length. RFC 5280 specifies that a CN 265 * must be between 1 and 64 bytes long. 266 */ 267 if (common_name_len < 1 || common_name_len > 64) { 268 tls_set_errorx(ctx, "error verifying name '%s': " 269 "Common Name field has invalid length, " 270 "probably a malicious certificate", name); 271 goto err; 272 } 273 /* 274 * Fail if the resulting text contains a NUL byte. 275 */ 276 if (memchr(utf8_bytes, 0, common_name_len) != NULL) { 277 tls_set_errorx(ctx, "error verifying name '%s': " 278 "NUL byte in Common Name field, " 279 "probably a malicious certificate", name); 280 goto err; 281 } 282 283 common_name = strndup(utf8_bytes, common_name_len); 284 if (common_name == NULL) { 285 tls_set_error(ctx, "out of memory"); 286 goto err; 287 } 288 289 /* 290 * We don't want to attempt wildcard matching against IP addresses, 291 * so perform a simple comparison here. 292 */ 293 if (inet_pton(AF_INET, name, &addrbuf) == 1 || 294 inet_pton(AF_INET6, name, &addrbuf) == 1) { 295 if (strcmp(common_name, name) == 0) 296 *cn_match = 1; 297 goto done; 298 } 299 300 if (tls_match_name(common_name, name) == 0) 301 *cn_match = 1; 302 303 done: 304 rv = 0; 305 306 err: 307 free(utf8_bytes); 308 free(common_name); 309 return rv; 310 } 311 312 int 313 tls_check_name(struct tls *ctx, X509 *cert, const char *name, int *match) 314 { 315 int alt_exists; 316 317 *match = 0; 318 319 if (tls_check_subject_altname(ctx, cert, name, match, 320 &alt_exists) == -1) 321 return -1; 322 323 /* 324 * As per RFC 6125 section 6.4.4, if any known alternate name existed 325 * in the certificate, we do not attempt to match on the CN. 326 */ 327 if (*match || alt_exists) 328 return 0; 329 330 return tls_check_common_name(ctx, cert, name, match); 331 } 332