Server crash in Empire 4.3.2

[Luigi Auriemma <aluigi@xxxxxxxxxxxxx>]

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                             Luigi Auriemma

Application:  Empire
              http://www.wolfpackempire.com
              http://sourceforge.net/projects/empserver
Versions:     <= 4.3.2
Platforms:    Windows, *nix, *BSD and more
Bug:          crash caused by strncat misuse
Exploitation: remote, versus server
Date:         12 May 2006
Author:       Luigi Auriemma
              e-mail: aluigi@xxxxxxxxxxxxx
              web:    aluigi.org


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1) Introduction
2) Bug
3) The Code
4) Fix


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


Empire is a well known multiplayer Internet war game.


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======
2) Bug
======


The bug is a server's crash caused by the access to an invalid zone of
the memory.
That happens due to the misuse of strncat in the client_cmd function
for adding the text strings sent by the attacker to the player->client
buffer.

>From lib/player/login.c:

static int
client_cmd(void)
{
    int i;

    if (!player->argp[1])
        return RET_SYN;

    for (i = 1; player->argp[i]; ++i) {
        if (i > 1)
            strncat(player->client, " ", sizeof(player->client) - 1);
        strncat(player->client, player->argp[i], sizeof(player->client) - 1);
    }
    player->client[sizeof(player->client) - 1] = '\0';
    pr_id(player, C_CMDOK, "talking to %s\n", player->client);
    return RET_OK;
}


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


http://aluigi.org/poc/empiredos.zip


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


Current CVS has been patched.
Anyway the following is the diff created by the developers:

--- login.c.~1.37.~     2006-04-26 20:50:40.000000000 +0200
+++ login.c     2006-05-09 08:36:04.000000000 +0200
@@ -133,17 +133,23 @@ player_login(void *ud)
 static int
 client_cmd(void)
 {
-    int i;
+    int i, sz;
+    char *p, *end;
 
     if (!player->argp[1])
        return RET_SYN;
 
+    p = player->client;
+    end = player->client + sizeof(player->client) - 1;
     for (i = 1; player->argp[i]; ++i) {
        if (i > 1)
-           strncat(player->client, " ", sizeof(player->client) - 1);
-       strncat(player->client, player->argp[i], sizeof(player->client) - 1);
+           *p++ = ' ';
+       sz = strlen(player->argp[i]);
+       sz = MIN(sz, end - p);
+       memcpy(p, player->argp[i], sz);
+       p += sz;
     }
-    player->client[sizeof(player->client) - 1] = '\0';
+    *p = 0;
     pr_id(player, C_CMDOK, "talking to %s\n", player->client);
     return RET_OK;
 }


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--- 
Luigi Auriemma
http://aluigi.org
http://mirror.aluigi.org