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Doomsday Multiple Vulnerabilities
------------------------------------------------------------------------
SUMMARY
Doomsday (aka deng) is an "open source port of the original Doom code with
tons of enhancements and addons which make it the most advanced port at
the moment". Multiple vulnerabilities has been discovered in Doomsday.
DETAILS
Vulnerable Systems:
* Doomsday version 1.9.0-beta5.1
D_NetPlayerEvent global buffer-overflow using PKT_CHAT:
When a chat message is received, the server takes the incoming packet and
reads who sent it, its destination and naturally the entire message which
is copied in a heap buffer using the remaining size of the packet for
calculating the amount of data to allocate. Then a strcpy() is performed
for copying the message from the packet to the new allocated buffer called
msg. If the message is directed to the server it's displayed in the
console using the D_NetPlayerEvent function. Subsequently the message is
copied from msg in a global buffer called netBuffer for sending the
message to all the other clients using the function MSG_Write.
This explanation is valid for the other three bugs below too since they
are exploited all through this same set of instructions which are showed
here:
from sv_main.c:
void Sv_HandlePacket(void)
...
case PKT_CHAT:
// The first byte contains the sender.
msgfrom = Msg_ReadByte();
// Is the message for us?
mask = Msg_ReadShort();
// Copy the message into a buffer.
msg = M_Malloc(netBuffer.length - 3);
strcpy(msg, (char *) netBuffer.cursor);
// Message for us? Show it locally.
if(mask & 1)
{
Net_ShowChatMessage();
gx.NetPlayerEvent(msgfrom, DDPE_CHAT_MESSAGE, msg);
}
// Servers relay chat messages to all the recipients.
Msg_Begin(PKT_CHAT);
Msg_WriteByte(msgfrom);
Msg_WriteShort(mask);
Msg_Write(msg, strlen(msg) + 1);
for(i = 1; i < MAXPLAYERS; i++)
if(players[i].ingame && mask & (1 << i) && i != from)
{
Net_SendBuffer(i, SPF_ORDERED);
}
M_Free(msg);
break;
In the case of D_NetPlayerEvent we have the following global buffer
overflow of msgBuff caused by a sprintf or strcpy depending by the number
of players in the server.
Important note: although this is a global buffer-overflow, on the Windows
game server (not the dedicated one) is possible to control the code flow
since EIP takes the value sent by the attacker, and so could be possible
to execute malicious code. Then this bug can be exploited not only versus
the servers but also versus all the clients connected since the big data
is forwarded to them by the same server.
from d_net.c:
char msgBuff[256];
float netJumpPower = 9;
..
long int D_NetPlayerEvent(int plrNumber, int peType, void *data)
...
// DDPE_CHAT_MESSAGE occurs when a PKT_CHAT is received.
// Here we will only display the message (if not a local message).
else if(peType == DDPE_CHAT_MESSAGE && plrNumber != consoleplayer)
...
// If there are more than two players, include the name of
// the player who sent this.
if(num > 2)
sprintf(msgBuff, "%s: %s", Net_GetPlayerName(plrNumber),
(const char *) data);
else
strcpy(msgBuff, data);
Msg_Write global buffer-overflow through PKT_CHAT:
The Msg_Write function used for filling the "send" buffer suffers of a
global buffer-overflow too, in this case the target buffer is netBuffer
which is 32768 bytes long.
from net_msg.c:
void Msg_Write(const void *src, int len)
{
memcpy(netBuffer.cursor, src, len);
netBuffer.cursor += len;
}
Undelimited strcpy in PKT_CHAT:
Although this specific bug has no reason of being exploited at the moment
due to the presence of the other more critical vulnerabilities I want to
report it for thoroughness. In fact in my tests after having patched the
above bugs my test server was still affected by a crash caused by the
absence of the final NULL byte in my chat messages which caused an
unexploitable heap-overflow of the msg buffer.
Integer overflow in PKT_CHAT:
As already said the size of the msg buffer is calculated through the size
of the packet but without the proper checks. The result is that an
attacker can send an incomplete PKT_CHAT packet which has a data length
minor than 3 causing the attempt of allocating a too big amount of memory
(for example 0xfffffffd, resulted by 0 - 3) which will fail and return a
NULL msg buffer causing a crash during the copying performed by strcpy:
mask = Msg_ReadShort();
// Copy the message into a buffer.
msg = M_Malloc(netBuffer.length - 3);
strcpy(msg, (char *) netBuffer.cursor);
Static buffer-overflow in NetSv_ReadCommands:
A static buffer-overflow is located in the function which reads the
commands sent by the clients allowing an attacker to fill the data buffer
with more than the 30 max commands supported.
from d_netsv.c:
void *NetSv_ReadCommands(byte *msg, uint size)
{
#define MAX_COMMANDS 30
static byte data[2 + sizeof(ticcmd_t) * MAX_COMMANDS];
ticcmd_t *cmd;
byte *end = msg + size, flags;
ushort *count = (ushort *) data;
memset(data, 0, sizeof(data));
// The first two bytes of the data contain the number of commands.
*count = 0;
// The first command.
cmd = (void *) (data + 2);
while(msg < end)
{
// One more command.
*count += 1;
// First the flags.
flags = *msg++;
if(flags & CMDF_FORWARDMOVE)
cmd->forwardMove = *msg++;
...
// Copy to next command (only differences have been written).
memcpy(cmd + 1, cmd, sizeof(ticcmd_t));
// Move to next command.
cmd++;
}
Client format string through PSV_CONSOLE_TEXT:
The clients are affected by a format string vulnerability exploitable
during the handling of a PSV_CONSOLE_TEXT message. This attack can be
exploited only through a malicious server to which the victim must
connect.
from cl_main.c:
void Cl_GetPackets(void)
...
case PSV_CONSOLE_TEXT:
i = Msg_ReadLong();
Con_FPrintf(i, (char*)netBuffer.cursor);
break;
PoC:
<http://aluigi.org/poc/dumsdei.zip> http://aluigi.org/poc/dumsdei.zip
ADDITIONAL INFORMATION
The information has been provided by Luigi Auriemma.
The original article can be found at:
<http://aluigi.altervista.org/adv/dumsdei-adv.txt>
http://aluigi.altervista.org/adv/dumsdei-adv.txt
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