1 /* $OpenBSD: tls_verify.c,v 1.30 2024/03/26 06:24:52 joshua 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, TLS_ERROR_UNKNOWN, 106 "error decoding subjectAltName"); 107 goto err; 108 } 109 goto done; 110 } 111 112 if (inet_pton(AF_INET, name, &addrbuf) == 1) { 113 type = GEN_IPADD; 114 addrlen = 4; 115 } else if (inet_pton(AF_INET6, name, &addrbuf) == 1) { 116 type = GEN_IPADD; 117 addrlen = 16; 118 } else { 119 type = GEN_DNS; 120 addrlen = 0; 121 } 122 123 count = sk_GENERAL_NAME_num(altname_stack); 124 for (i = 0; i < count; i++) { 125 GENERAL_NAME *altname; 126 127 altname = sk_GENERAL_NAME_value(altname_stack, i); 128 129 if (altname->type == GEN_DNS || altname->type == GEN_IPADD) 130 *alt_exists = 1; 131 132 if (altname->type != type) 133 continue; 134 135 if (type == GEN_DNS) { 136 const unsigned char *data; 137 int format, len; 138 139 format = ASN1_STRING_type(altname->d.dNSName); 140 if (format == V_ASN1_IA5STRING) { 141 data = ASN1_STRING_get0_data(altname->d.dNSName); 142 len = ASN1_STRING_length(altname->d.dNSName); 143 144 if (len < 0 || (size_t)len != strlen(data)) { 145 tls_set_errorx(ctx, TLS_ERROR_UNKNOWN, 146 "error verifying name '%s': " 147 "NUL byte in subjectAltName, " 148 "probably a malicious certificate", 149 name); 150 goto err; 151 } 152 153 /* 154 * Per RFC 5280 section 4.2.1.6: 155 * " " is a legal domain name, but that 156 * dNSName must be rejected. 157 */ 158 if (strcmp(data, " ") == 0) { 159 tls_set_errorx(ctx, TLS_ERROR_UNKNOWN, 160 "error verifying name '%s': " 161 "a dNSName of \" \" must not be " 162 "used", name); 163 goto err; 164 } 165 166 if (tls_match_name(data, name) == 0) { 167 *alt_match = 1; 168 goto done; 169 } 170 } else { 171 #ifdef DEBUG 172 fprintf(stdout, "%s: unhandled subjectAltName " 173 "dNSName encoding (%d)\n", getprogname(), 174 format); 175 #endif 176 } 177 178 } else if (type == GEN_IPADD) { 179 const unsigned char *data; 180 int datalen; 181 182 datalen = ASN1_STRING_length(altname->d.iPAddress); 183 data = ASN1_STRING_get0_data(altname->d.iPAddress); 184 185 if (datalen < 0) { 186 tls_set_errorx(ctx, TLS_ERROR_UNKNOWN, 187 "Unexpected negative length for an " 188 "IP address: %d", datalen); 189 goto err; 190 } 191 192 /* 193 * Per RFC 5280 section 4.2.1.6: 194 * IPv4 must use 4 octets and IPv6 must use 16 octets. 195 */ 196 if (datalen == addrlen && 197 memcmp(data, &addrbuf, addrlen) == 0) { 198 *alt_match = 1; 199 goto done; 200 } 201 } 202 } 203 204 done: 205 rv = 0; 206 207 err: 208 sk_GENERAL_NAME_pop_free(altname_stack, GENERAL_NAME_free); 209 return rv; 210 } 211 212 static int 213 tls_check_common_name(struct tls *ctx, X509 *cert, const char *name, 214 int *cn_match) 215 { 216 unsigned char *utf8_bytes = NULL; 217 X509_NAME *subject_name; 218 char *common_name = NULL; 219 union tls_addr addrbuf; 220 int common_name_len; 221 ASN1_STRING *data; 222 int lastpos = -1; 223 int rv = -1; 224 225 *cn_match = 0; 226 227 subject_name = X509_get_subject_name(cert); 228 if (subject_name == NULL) 229 goto done; 230 231 lastpos = X509_NAME_get_index_by_NID(subject_name, 232 NID_commonName, lastpos); 233 if (lastpos == -1) 234 goto done; 235 if (lastpos < 0) 236 goto err; 237 if (X509_NAME_get_index_by_NID(subject_name, NID_commonName, lastpos) 238 != -1) { 239 /* 240 * Having multiple CN's is possible, and even happened back in 241 * the glory days of mullets and Hammer pants. In anything like 242 * a modern TLS cert, CN is as close to deprecated as it gets, 243 * and having more than one is bad. We therefore fail if we have 244 * more than one CN fed to us in the subject, treating the 245 * certificate as hostile. 246 */ 247 tls_set_errorx(ctx, TLS_ERROR_UNKNOWN, 248 "error verifying name '%s': " 249 "Certificate subject contains multiple Common Name fields, " 250 "probably a malicious or malformed certificate", name); 251 goto err; 252 } 253 254 data = X509_NAME_ENTRY_get_data(X509_NAME_get_entry(subject_name, 255 lastpos)); 256 /* 257 * Fail if we cannot encode the CN bytes as UTF-8. 258 */ 259 if ((common_name_len = ASN1_STRING_to_UTF8(&utf8_bytes, data)) < 0) { 260 tls_set_errorx(ctx, TLS_ERROR_UNKNOWN, 261 "error verifying name '%s': " 262 "Common Name field cannot be encoded as a UTF-8 string, " 263 "probably a malicious certificate", name); 264 goto err; 265 } 266 /* 267 * Fail if the CN is of invalid length. RFC 5280 specifies that a CN 268 * must be between 1 and 64 bytes long. 269 */ 270 if (common_name_len < 1 || common_name_len > 64) { 271 tls_set_errorx(ctx, TLS_ERROR_UNKNOWN, 272 "error verifying name '%s': " 273 "Common Name field has invalid length, " 274 "probably a malicious certificate", name); 275 goto err; 276 } 277 /* 278 * Fail if the resulting text contains a NUL byte. 279 */ 280 if (memchr(utf8_bytes, 0, common_name_len) != NULL) { 281 tls_set_errorx(ctx, TLS_ERROR_UNKNOWN, 282 "error verifying name '%s': " 283 "NUL byte in Common Name field, " 284 "probably a malicious certificate", name); 285 goto err; 286 } 287 288 common_name = strndup(utf8_bytes, common_name_len); 289 if (common_name == NULL) { 290 tls_set_error(ctx, TLS_ERROR_OUT_OF_MEMORY, 291 "out of memory"); 292 goto err; 293 } 294 295 /* 296 * We don't want to attempt wildcard matching against IP addresses, 297 * so perform a simple comparison here. 298 */ 299 if (inet_pton(AF_INET, name, &addrbuf) == 1 || 300 inet_pton(AF_INET6, name, &addrbuf) == 1) { 301 if (strcmp(common_name, name) == 0) 302 *cn_match = 1; 303 goto done; 304 } 305 306 if (tls_match_name(common_name, name) == 0) 307 *cn_match = 1; 308 309 done: 310 rv = 0; 311 312 err: 313 free(utf8_bytes); 314 free(common_name); 315 return rv; 316 } 317 318 int 319 tls_check_name(struct tls *ctx, X509 *cert, const char *name, int *match) 320 { 321 int alt_exists; 322 323 *match = 0; 324 325 if (tls_check_subject_altname(ctx, cert, name, match, 326 &alt_exists) == -1) 327 return -1; 328 329 /* 330 * As per RFC 6125 section 6.4.4, if any known alternate name existed 331 * in the certificate, we do not attempt to match on the CN. 332 */ 333 if (*match || alt_exists) 334 return 0; 335 336 return tls_check_common_name(ctx, cert, name, match); 337 } 338