full-disclosure - [SST]ServU MDTM command remote buffero verflow adv

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Message-ID: <200401240749.i0O7npU24383@netsys.com>
From: icbm at 0x557.net (icbm)
Subject: [SST]ServU MDTM command remote buffero verflow adv

Serv-U Ftp Server Long Filename Stack Overflow Vunlnerablity

Application:           Serv-U

Affected Versions:     All versions prior 4.2 (include 4.1.0.11) 

Vendor:                RhinoSoft (http://www.rhinosoft.com 
                       http://www.serv-u.com)

URL:                   http://www.0x557.org/release/servu.txt

Vunlnerablity:

  An internal memory buffer may be overrun while handling "site chmod" command 
with a filename containg excessive data. This condition may be exploited by 
attackers to ultimately execute instructions with the priviledges of the serv-u
process, typically administator or system.

Details:

  While exectuing chmod on a nonexistent file, serv-u will call sprintf to
construct response string. And the code is like
  sprintf(dst, "%s: No such file or directory.", filename);

  The length of dst buffer is only 256 bytes.If a long filename was sent,
serv-u will crash.

  A writable directory is needed to exploit this vulerablity.By overwriting SEH,
we have created proof-of-concept exploit successfully on win2k/xp.

Solution:

  Upgrade to servu 5.0.

Credits:

  kkqq <kkqq@...57.org> has indenpendently discovered this vulerablity.
  All members of SST (http://www.0x557.org).
  lgx and eyas.
  Rob Beckers for indentifing and fixing this vulerablity.

About SST:

  Do we really exist? 

　　　　　　　　icbm
　　　　　　　　icbm@...57.net
　　　　　　　　　　2004-01-24