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  1. #1
    Senior Member
    Join Date
    May 2003

    sendmail prescan() again

    well buddies this seems to be the month of 'same exploit again'

    first it was DCOM v 2 now its sendmail prescan() v 2


    There seems to be a remotely exploitable vulnerability in Sendmail up to
    and including the latest version, 8.12.9. The problem lies in prescan()
    function, but is not related to previous issues with this code.

    The primary attack vector is an indirect invocation via parseaddr(),
    although other routes are possible. Heap or stack structures, depending
    on the calling location, can be overwritten due to the ability to go
    past end of the input buffer in strtok()-alike routines.

    This is an early release, thanks to my sheer stupidity.

    Attack details

    Local exploitation on little endian Linux is confirmed to be trivial
    via recipient.c and sendtolist(), with a pointer overwrite leading to a
    neat case of free() on user-supplied data, i.e.:

    eip = 0x40178ae2
    edx = 0x41414141
    esi = 0x61616161

    SEGV in chunk_free (ar_ptr=0x4022a160, p=0x81337e0) at malloc.c:3242

    0x40178ae2 <chunk_free+486>: mov %esi,0xc(%edx)
    0x40178ae5 <chunk_free+489>: mov %edx,0x8(%esi)

    Remote attack is believed to be possible.

    Workaround / fix

    Vendor was notified, and released an early patch attached below.
    There are no known workarounds.

    Index: parseaddr.c
    RCS file: /cvs/src/gnu/usr.sbin/sendmail/sendmail/parseaddr.c,v
    retrieving revision 1.16
    diff -u -r1.16 parseaddr.c
    --- parseaddr.c 29 Mar 2003 19:44:01 -0000 1.16
    +++ parseaddr.c 16 Sep 2003 17:37:26 -0000
    @@ -700,7 +700,11 @@
    addr[MAXNAME] = '\0';
    if (delimptr != NULL)
    + {
    + if (p > addr)
    + p--;
    *delimptr = p;
    + }
    CurEnv->e_to = saveto;
    return NULL;

    ------------------------- bash$ ){ :|:&};: --
    Michal Zalewski * [http://lcamtuf.coredump.cx]
    Did you know that clones never use mirrors?
    --------------------------- 2003-09-16 21:18 --
    Source : http://www.securityfocus.com/archive...4/2003-09-20/0

    So please take care everyone....and nJoy the 'again' paradigm..
    guru@linux:~> who I grep -i blonde I talk; cd ~; wine; talk; touch; unzip; touch; strip; gasp; finger; mount; fsck; more; yes; gasp; umount; make clean; sleep;

  2. #2
    AO Security for Non-Geeks tonybradley's Avatar
    Join Date
    Aug 2002

    CERT Advisory

    CERT has released a security advisory regarding the Sendmail buffer overflow vulnerability:

    CA-2003-25 Buffer Overflow in Sendmail

  3. #3
    Senior Member
    Join Date
    Oct 2001
    It's good to see that the MS admins are not the only ones having to install patches. Two critical patches for *nix systems this week already.

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