[Dshield] Broadcast BoF and server freeze in RogerWilco (2001)

Auriemma Luigi aluigi at pivx.com
Wed Jul 2 15:32:45 GMT 2003


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Application:  Roger Wilco (http://www.rogerwilco.com)
Versions:     Mk.1d3 dated 14th Sep 2001 (1.4.1.2 is NOT vulnerable)
Platforms:    Windows
Bugs:         RogerWilco doesn't check the length of the nicknames sent
              by the clients and exists also a problem in a recv()
              function
Risk (HIGH!): "Broadcast" buffer overflow and server freeze
Author:       Auriemma Luigi
              e-mail: aluigi at pivx.com
              web:    http://www.pivx.com/luigi/


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1) Introduction
2) Bugs
3) The Code
4) Fix
5) Philosophy


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===============
1) Introduction
===============


Roger Wilco is probably the most famous tool that lets gamers to speak
together during the matches with their preferred games.
It is shareware and is developed by Gamespy.



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=======
2) Bugs
=======


The 2 bugs I have found affect ONLY the main graphical program
(roger.exe), NOT the dedicated server:



-----------------------------
[A] Broadcast buffer overflow
-----------------------------


This bug is just the perfect situation to make tons of damage using the
minumum energy.
Until now I have never found a "broadcast" buffer overflow, so I'm very
interested about.

This buffer overflow happens when a client that connects to the server
sends a nickname string too long (a classical BoF...).
The nickname must be at least 516 bytes long to overwrite the return
address of EVERY client that receive this nickname.

In fact the server (both normal and dedicated server) will send the
nickname field in broadcast to ALL the clients connected to it.
That mean that ALL the clients connected to the server (the graphical
program become both server and client when hosts a channel) will
execute the malicious code in the nickname field sent by the attacker!



Now a bit of assembly for who is interested in the details:

The vulnerable function starts at offset 0x40a1b0 of roger.exe
The instructions that cause the overwriting of the return address are
the following:


:0040A200 8BF7                    mov esi, edi
:0040A202 8B7C2414                mov edi, dword ptr [esp+14]
:0040A206 C1E902                  shr ecx, 02
:0040A209 F3A5                    repz movsd

:0040A200   ESI will point to the beginning of the nickname sent by the
            client ("aaaaaaaaaaaaaaaaaaaaaa...")
:0040A202   now the address of the destination buffer will be copied
            into EDI register
:0040A206   the size of the data will be divided for 4 (it copies 32
            bits each time)
:0040A209   it copies the bytes that starts at the address pointed by
            ESI to the new buffer overwriting the return address stored
            at offset 0x0068f080 (the right return address stored before
            the BoF was 0x00409304)


When RogerWilco executes the instruction at offset 0x0040A209 the
return address stored at offset 0x0068f080 will be fully overwritten.





-----------------
[B] Server freeze
-----------------


A client can connect to the server that hosts a channel and instead of
sending a full packet it sends it partially.
The "join-packet" contains all the data of the client as the channel
it wants to join to, the password for the channel, its nickname and
some other little informations.

The problem happens when the client uses the nickname tag ("\x0f\x10")
BUT doesn't complete the packet with all the other needed informations.
An example is the following packet:

"\x0f\x00"
"\x00\x14"
"\x6a\xd6\x4c\x03\x96\xed\x3b\xe7\x88\xe2\xa9\x74"
"channel\0"
"\x0f\x10"
   <-- here there is nothing!


As you can see there is nothing after the nickname tag.


The problem happens in NETWORK.DLL when the program calls the function
WSOCK32.recv:

---
:100027B1 51                      push ecx

* Reference To: WSOCK32.recv, Ord:0010h
                                  |
:100027B2 E8BF440000              Call 10006C76
:100027B7 CC                      int 03
---

In fact the recv() function will NOT return until the malicious client
is connected to the server (probably because it waits the other pieces
of data that the attacker has not sent).

When the attacker will disconnect itself, the situation will return
normally.



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===========
3) The Code
===========


I have written a program that tests the 2 bugs I have found.
You can choose your nickname, the channel to join, the relative
password to use, the port to connect to, using the autorejoin option
(so you can rejoin infinitely), getting remote informations and
naturally you can also see what happens in realtime on the server, as
who enters, who exits, relative IP addresses, who changes his nickname
and other little informations.
Naturally, as almost all my tools, it can be compiled on both Unix and
Windows:


http://www.pivx.com/luigi/poc/wilco.zip




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======
4) Fix
======


RogerWilco supports the autoupdate feauture so you should already have
the patched version, however the latest (1.4.1.2) released 16th June
2003 is available on the official homepage:

http://www.rogerwilco.com



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=============
5) Philosophy
=============


Be free.
Researchers'community needs your reversing, your programs and your
research, so don't stop your passion and your work!



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Any type of feedback is really welcome!


BYEZ




--- 
Researcher
http://www.pivx.com/luigi/





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