/*************************************************************************** * ncat_ssl.c -- SSL support functions. * ***********************IMPORTANT NMAP LICENSE TERMS************************ * * * The Nmap Security Scanner is (C) 1996-2012 Insecure.Com LLC. Nmap is * * also a registered trademark of Insecure.Com LLC. This program is free * * software; you may redistribute and/or modify it under the terms of the * * GNU General Public License as published by the Free Software * * Foundation; Version 2 with the clarifications and exceptions described * * below. This guarantees your right to use, modify, and redistribute * * this software under certain conditions. If you wish to embed Nmap * * technology into proprietary software, we sell alternative licenses * * (contact sales@insecure.com). Dozens of software vendors already * * license Nmap technology such as host discovery, port scanning, OS * * detection, version detection, and the Nmap Scripting Engine. * * * * Note that the GPL places important restrictions on "derived works", yet * * it does not provide a detailed definition of that term. To avoid * * misunderstandings, we interpret that term as broadly as copyright law * * allows. For example, we consider an application to constitute a * * "derivative work" for the purpose of this license if it does any of the * * following: * * o Integrates source code from Nmap * * o Reads or includes Nmap copyrighted data files, such as * * nmap-os-db or nmap-service-probes. * * o Executes Nmap and parses the results (as opposed to typical shell or * * execution-menu apps, which simply display raw Nmap output and so are * * not derivative works.) * * o Integrates/includes/aggregates Nmap into a proprietary executable * * installer, such as those produced by InstallShield. * * o Links to a library or executes a program that does any of the above * * * * The term "Nmap" should be taken to also include any portions or derived * * works of Nmap, as well as other software we distribute under this * * license such as Zenmap, Ncat, and Nping. This list is not exclusive, * * but is meant to clarify our interpretation of derived works with some * * common examples. Our interpretation applies only to Nmap--we don't * * speak for other people's GPL works. * * * * If you have any questions about the GPL licensing restrictions on using * * Nmap in non-GPL works, we would be happy to help. As mentioned above, * * we also offer alternative license to integrate Nmap into proprietary * * applications and appliances. These contracts have been sold to dozens * * of software vendors, and generally include a perpetual license as well * * as providing for priority support and updates. They also fund the * * continued development of Nmap. Please email sales@insecure.com for * * further information. * * * * As a special exception to the GPL terms, Insecure.Com LLC grants * * permission to link the code of this program with any version of the * * OpenSSL library which is distributed under a license identical to that * * listed in the included docs/licenses/OpenSSL.txt file, and distribute * * linked combinations including the two. You must obey the GNU GPL in all * * respects for all of the code used other than OpenSSL. If you modify * * this file, you may extend this exception to your version of the file, * * but you are not obligated to do so. * * * * If you received these files with a written license agreement or * * contract stating terms other than the terms above, then that * * alternative license agreement takes precedence over these comments. * * * * Source is provided to this software because we believe users have a * * right to know exactly what a program is going to do before they run it. * * This also allows you to audit the software for security holes (none * * have been found so far). * * * * Source code also allows you to port Nmap to new platforms, fix bugs, * * and add new features. You are highly encouraged to send your changes * * to nmap-dev@insecure.org for possible incorporation into the main * * distribution. By sending these changes to Fyodor or one of the * * Insecure.Org development mailing lists, or checking them into the Nmap * * source code repository, it is understood (unless you specify otherwise) * * that you are offering the Nmap Project (Insecure.Com LLC) the * * unlimited, non-exclusive right to reuse, modify, and relicense the * * code. Nmap will always be available Open Source, but this is important * * because the inability to relicense code has caused devastating problems * * for other Free Software projects (such as KDE and NASM). We also * * occasionally relicense the code to third parties as discussed above. * * If you wish to specify special license conditions of your * * contributions, just say so when you send them. * * * * This program is distributed in the hope that it will be useful, but * * WITHOUT ANY WARRANTY; without even the implied warranty of * * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * * General Public License v2.0 for more details at * * http://www.gnu.org/licenses/gpl-2.0.html , or in the COPYING file * * included with Nmap. * * * ***************************************************************************/ /* $Id$ */ #include "nbase.h" #include "ncat_config.h" #ifdef HAVE_OPENSSL #include "nsock.h" #include "ncat.h" #include #include #include #include #include #include #include /* Required for windows compilation to Eliminate APPLINK errors. See http://www.openssl.org/support/faq.html#PROG2 */ #ifdef WIN32 #include #endif static SSL_CTX *sslctx; static int ssl_gen_cert(X509 **cert, EVP_PKEY **key); /* Parameters for automatic key and certificate generation. */ enum { DEFAULT_KEY_BITS = 1024, DEFAULT_CERT_DURATION = 60 * 60 * 24 * 365, }; #define CERTIFICATE_COMMENT "Automatically generated by Ncat. See http://nmap.org/ncat/." SSL_CTX *setup_ssl_listen(void) { const SSL_METHOD *method; if (sslctx) goto done; SSL_library_init(); OpenSSL_add_all_algorithms(); ERR_load_crypto_strings(); SSL_load_error_strings(); /* RAND_status initializes the random number generator through a variety of platform-dependent methods, then returns 1 if there is enough entropy or 0 otherwise. This seems to be a good platform-independent way of seeding the generator, as well as of refusing to continue without enough entropy. */ if (!RAND_status()) bye("Failed to seed OpenSSL PRNG (RAND_status returned false)."); if (!(method = SSLv23_server_method())) bye("SSLv23_server_method(): %s.", ERR_error_string(ERR_get_error(), NULL)); if (!(sslctx = SSL_CTX_new(method))) bye("SSL_CTX_new(): %s.", ERR_error_string(ERR_get_error(), NULL)); SSL_CTX_set_options(sslctx, SSL_OP_ALL | SSL_OP_NO_SSLv2); /* Secure ciphers list taken from Nsock. */ if (!SSL_CTX_set_cipher_list(sslctx, "ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH")) bye("Unable to set OpenSSL cipher list: %s", ERR_error_string(ERR_get_error(), NULL)); if (o.sslcert == NULL && o.sslkey == NULL) { X509 *cert; EVP_PKEY *key; char digest_buf[SHA1_STRING_LENGTH + 1]; if (o.verbose) loguser("Generating a temporary %d-bit RSA key. Use --ssl-key and --ssl-cert to use a permanent one.\n", DEFAULT_KEY_BITS); if (ssl_gen_cert(&cert, &key) == 0) bye("ssl_gen_cert(): %s.", ERR_error_string(ERR_get_error(), NULL)); if (o.verbose) { assert(ssl_cert_fp_str_sha1(cert, digest_buf, sizeof(digest_buf)) != NULL); loguser("SHA-1 fingerprint: %s\n", digest_buf); } if (SSL_CTX_use_certificate(sslctx, cert) != 1) bye("SSL_CTX_use_certificate(): %s.", ERR_error_string(ERR_get_error(), NULL)); if (SSL_CTX_use_PrivateKey(sslctx, key) != 1) bye("SSL_CTX_use_PrivateKey(): %s.", ERR_error_string(ERR_get_error(), NULL)); X509_free(cert); EVP_PKEY_free(key); } else { if (o.sslcert == NULL || o.sslkey == NULL) bye("The --ssl-key and --ssl-cert options must be used together."); if (SSL_CTX_use_certificate_file(sslctx, o.sslcert, SSL_FILETYPE_PEM) != 1) bye("SSL_CTX_use_certificate_file(): %s.", ERR_error_string(ERR_get_error(), NULL)); if (SSL_CTX_use_PrivateKey_file(sslctx, o.sslkey, SSL_FILETYPE_PEM) != 1) bye("SSL_CTX_use_Privatekey_file(): %s.", ERR_error_string(ERR_get_error(), NULL)); } done: return sslctx; } SSL *new_ssl(int fd) { SSL *ssl; if (!(ssl = SSL_new(sslctx))) bye("SSL_new(): %s.", ERR_error_string(ERR_get_error(), NULL)); if (!SSL_set_fd(ssl, fd)) bye("SSL_set_fd(): %s.", ERR_error_string(ERR_get_error(), NULL)); return ssl; } /* Match a (user-supplied) hostname against a (certificate-supplied) name, which may be a wildcard pattern. A wildcard pattern may contain only one '*', it must be the entire leftmost component, and there must be at least two components following it. len is the length of pattern; pattern may contain null bytes so that len != strlen(pattern). */ static int wildcard_match(const char *pattern, const char *hostname, size_t len) { if (pattern[0] == '*' && pattern[1] == '.') { /* A wildcard pattern. */ const char *p, *h, *dot; /* Skip the wildcard component. */ p = pattern + 2; /* Ensure there are no more wildcard characters. */ if (memchr(p, '*', len - 2) != NULL) return 0; /* Ensure there's at least one more dot, not counting a dot at the end. */ dot = strchr(p, '.'); if (dot == NULL || *(dot + 1) == '\0') { if (o.debug > 1) { logdebug("Wildcard name \"%s\" doesn't have at least two" " components after the wildcard; rejecting.\n", pattern); } return 0; } /* Skip the leftmost hostname component. */ h = strchr(hostname, '.'); if (h == NULL) return 0; h++; /* Compare what remains of the pattern and hostname. */ return len == strlen(h) + (p - pattern) && strcmp(p, h) == 0; } else { /* Normal string comparison. Check the name length because I'm concerned about someone somehow embedding a '\0' in the subject and matching against a shorter name. */ return len == strlen(hostname) && strcmp(pattern, hostname) == 0; } } /* Match a hostname against the contents of a dNSName field of the subjectAltName extension, if present. This is the preferred place for a certificate to store its domain name, as opposed to in the commonName field. It has the advantage that multiple names can be stored, so that one certificate can match both "example.com" and "www.example.com". If num_checked is not NULL, the number of dNSName fields that were checked before returning will be stored in it. This is so you can distinguish between the check failing because there were names but none matched, or because there were no names to match. */ static int cert_match_dnsname(X509 *cert, const char *hostname, unsigned int *num_checked) { X509_EXTENSION *ext; STACK_OF(GENERAL_NAME) *gen_names; const X509V3_EXT_METHOD *method; unsigned char *data; int i; if (num_checked != NULL) *num_checked = 0; i = X509_get_ext_by_NID(cert, NID_subject_alt_name, -1); if (i < 0) return 0; /* If there's more than one subjectAltName extension, forget it. */ if (X509_get_ext_by_NID(cert, NID_subject_alt_name, i) >= 0) return 0; ext = X509_get_ext(cert, i); /* See the function X509V3_EXT_print in the OpenSSL source for this method of getting a string value from an extension. */ method = X509V3_EXT_get(ext); if (method == NULL) return 0; /* We must copy this address into a temporary variable because ASN1_item_d2i increments it. We don't want it to corrupt ext->value->data. */ data = ext->value->data; /* Here we rely on the fact that the internal representation (the "i" in "i2d") for NID_subject_alt_name is STACK_OF(GENERAL_NAME). Converting it to a stack of CONF_VALUE with a i2v method is not satisfactory, because a CONF_VALUE doesn't contain the length of the value so you can't know the presence of null bytes. */ #if (OPENSSL_VERSION_NUMBER > 0x00907000L) if (method->it != NULL) { gen_names = (STACK_OF(GENERAL_NAME) *) ASN1_item_d2i(NULL, (const unsigned char **) &data, ext->value->length, ASN1_ITEM_ptr(method->it)); } else { gen_names = (STACK_OF(GENERAL_NAME) *) method->d2i(NULL, (const unsigned char **) &data, ext->value->length); } #else gen_names = (STACK_OF(GENERAL_NAME) *) method->d2i(NULL, (const unsigned char **) &data, ext->value->length); #endif if (gen_names == NULL) return 0; /* Look for a dNSName field with a matching hostname. There may be more than one dNSName field. */ for (i = 0; i < sk_GENERAL_NAME_num(gen_names); i++) { GENERAL_NAME *gen_name; gen_name = sk_GENERAL_NAME_value(gen_names, i); if (gen_name->type == GEN_DNS) { if (o.debug > 1) logdebug("Checking certificate DNS name \"%s\" against \"%s\".\n", ASN1_STRING_data(gen_name->d.dNSName), hostname); if (num_checked != NULL) (*num_checked)++; if (wildcard_match((char *) ASN1_STRING_data(gen_name->d.dNSName), hostname, ASN1_STRING_length(gen_name->d.dNSName))) return 1; } } return 0; } /* Returns the number of contiguous blocks of bytes in pattern that do not contain the '.' byte. */ static unsigned int num_components(const unsigned char *pattern, size_t len) { const unsigned char *p; unsigned int count; count = 0; p = pattern; for (;;) { while (p - pattern < len && *p == '.') p++; if (p - pattern >= len) break; while (p - pattern < len && *p != '.') p++; count++; } return count; } /* Returns true if the a pattern is strictly less specific than the b pattern. */ static int less_specific(const unsigned char *a, size_t a_len, const unsigned char *b, size_t b_len) { /* Wildcard patterns are always less specific than non-wildcard patterns. */ if (memchr(a, '*', a_len) != NULL && memchr(b, '*', b_len) == NULL) return 1; if (memchr(a, '*', a_len) == NULL && memchr(b, '*', b_len) != NULL) return 0; return num_components(a, a_len) < num_components(b, b_len); } static int most_specific_commonname(X509_NAME *subject, const char **result) { ASN1_STRING *best, *cur; int i; i = -1; best = NULL; while ((i = X509_NAME_get_index_by_NID(subject, NID_commonName, i)) != -1) { cur = X509_NAME_ENTRY_get_data(X509_NAME_get_entry(subject, i)); /* We use "not less specific" instead of "more specific" to allow later entries to supersede earlier ones. */ if (best == NULL || !less_specific(ASN1_STRING_data(cur), ASN1_STRING_length(cur), ASN1_STRING_data(best), ASN1_STRING_length(best))) { best = cur; } } if (best == NULL) { *result = NULL; return -1; } else { *result = (char *) ASN1_STRING_data(best); return ASN1_STRING_length(best); } } /* Match a hostname against the contents of the "most specific" commonName field of a certificate. The "most specific" term is used in RFC 2818 but is not defined anywhere that I (David Fifield) can find. This is what it means in Ncat: wildcard patterns are always less specific than non-wildcard patterns. If both patterns are wildcard or both are non-wildcard, the one with more name components is more specific. If two names have the same number of components, the one that comes later in the certificate is more specific. */ static int cert_match_commonname(X509 *cert, const char *hostname) { X509_NAME *subject; const char *commonname; int n; subject = X509_get_subject_name(cert); if (subject == NULL) return 0; n = most_specific_commonname(subject, &commonname); if (n < 0 || commonname == NULL) /* No commonName found. */ return 0; if (wildcard_match(commonname, hostname, n)) return 1; if (o.verbose) loguser("Certificate verification error: Connected to \"%s\", but certificate is for \"%s\".\n", hostname, commonname); return 0; } /* Verify a host's name against the name in its certificate after connection. If the verify mode is SSL_VERIFY_NONE, always returns true. Returns nonzero on success. */ int ssl_post_connect_check(SSL *ssl, const char *hostname) { X509 *cert = NULL; unsigned int num_checked; if (SSL_get_verify_mode(ssl) == SSL_VERIFY_NONE) return 1; if (hostname == NULL) return 0; cert = SSL_get_peer_certificate(ssl); if (cert == NULL) return 0; /* RFC 2818 (HTTP Over TLS): If a subjectAltName extension of type dNSName is present, that MUST be used as the identity. Otherwise, the (most specific) Common Name field in the Subject field of the certificate MUST be used. Although the use of the Common Name is existing practice, it is deprecated and Certification Authorities are encouraged to use the dNSName instead. */ if (!cert_match_dnsname(cert, hostname, &num_checked)) { /* If there were dNSNames, we're done. If not, try the commonNames. */ if (num_checked > 0 || !cert_match_commonname(cert, hostname)) { X509_free(cert); return 0; } } X509_free(cert); return SSL_get_verify_result(ssl) == X509_V_OK; } /* Generate a self-signed certificate and matching RSA keypair. References for this code are the book Network Programming with OpenSSL, chapter 10, section "Making Certificates"; and apps/req.c in the OpenSSL source. */ static int ssl_gen_cert(X509 **cert, EVP_PKEY **key) { RSA *rsa; X509_NAME *subj; X509_EXTENSION *ext; X509V3_CTX ctx; const char *commonName = "localhost"; char dNSName[128]; int rc; *cert = NULL; *key = NULL; /* Generate a private key. */ *key = EVP_PKEY_new(); if (*key == NULL) goto err; do { rsa = RSA_generate_key(DEFAULT_KEY_BITS, RSA_F4, NULL, NULL); if (rsa == NULL) goto err; rc = RSA_check_key(rsa); } while (rc == 0); if (rc == -1) bye("Error generating RSA key: %s", ERR_error_string(ERR_get_error(), NULL)); if (EVP_PKEY_assign_RSA(*key, rsa) == 0) { RSA_free(rsa); goto err; } /* Generate a certificate. */ *cert = X509_new(); if (*cert == NULL) goto err; if (X509_set_version(*cert, 2) == 0) /* Version 3. */ goto err; ASN1_INTEGER_set(X509_get_serialNumber(*cert), get_random_u32() & 0x7FFFFFFF); /* Set the commonName. */ subj = X509_get_subject_name(*cert); if (o.target != NULL) commonName = o.target; if (X509_NAME_add_entry_by_txt(subj, "commonName", MBSTRING_ASC, (unsigned char *) commonName, -1, -1, 0) == 0) { goto err; } /* Set the dNSName. */ rc = Snprintf(dNSName, sizeof(dNSName), "DNS:%s", commonName); if (rc < 0 || rc >= sizeof(dNSName)) goto err; X509V3_set_ctx(&ctx, *cert, *cert, NULL, NULL, 0); ext = X509V3_EXT_conf(NULL, &ctx, "subjectAltName", dNSName); if (ext == NULL) goto err; if (X509_add_ext(*cert, ext, -1) == 0) goto err; /* Set a comment. */ ext = X509V3_EXT_conf(NULL, &ctx, "nsComment", CERTIFICATE_COMMENT); if (ext == NULL) goto err; if (X509_add_ext(*cert, ext, -1) == 0) goto err; if (X509_set_issuer_name(*cert, X509_get_subject_name(*cert)) == 0 || X509_gmtime_adj(X509_get_notBefore(*cert), 0) == 0 || X509_gmtime_adj(X509_get_notAfter(*cert), DEFAULT_CERT_DURATION) == 0 || X509_set_pubkey(*cert, *key) == 0) { goto err; } /* Sign it. */ if (X509_sign(*cert, *key, EVP_sha1()) == 0) goto err; return 1; err: if (*cert != NULL) X509_free(*cert); if (*key != NULL) EVP_PKEY_free(*key); return 0; } /* Calculate a SHA-1 fingerprint of a certificate and format it as a human-readable string. Returns strbuf or NULL on error. */ char *ssl_cert_fp_str_sha1(const X509 *cert, char *strbuf, size_t len) { unsigned char binbuf[SHA1_BYTES]; unsigned int n; char *p; unsigned int i; if (len < SHA1_STRING_LENGTH + 1) return NULL; n = sizeof(binbuf); if (X509_digest(cert, EVP_sha1(), binbuf, &n) != 1) return NULL; p = strbuf; for (i = 0; i < n; i++) { if (i > 0 && i % 2 == 0) *p++ = ' '; Snprintf(p, 3, "%02X", binbuf[i]); p += 2; } assert(p - strbuf <= len); *p = '\0'; return strbuf; } /* Tries to complete an ssl handshake on the socket received by fdinfo struct if ssl is enabled on that socket. */ int ssl_handshake(struct fdinfo *sinfo) { int ret = 0; int sslerr = 0; if(sinfo == NULL) { if (o.debug) logdebug("ncat_ssl.c: Invoking ssl_handshake() with a NULL parameter " "is a serious bug. Please fix it.\n"); return -1; } if(!o.ssl) return -1; /* Initialize the socket too if it isn't. */ if(!sinfo->ssl) sinfo->ssl = new_ssl(sinfo->fd); ret = SSL_accept(sinfo->ssl); if(ret == 1) return NCAT_SSL_HANDSHAKE_COMPLETED; sslerr = SSL_get_error(sinfo->ssl, ret); if(ret == -1) { if(sslerr == SSL_ERROR_WANT_READ) return NCAT_SSL_HANDSHAKE_PENDING_READ; if(sslerr == SSL_ERROR_WANT_WRITE) return NCAT_SSL_HANDSHAKE_PENDING_WRITE; } if (o.verbose) { loguser("Failed SSL connection from %s: %s\n", inet_socktop(&sinfo->remoteaddr), ERR_error_string(ERR_get_error(), NULL)); } return NCAT_SSL_HANDSHAKE_FAILED; } #endif