OpenSIPS: protecting from undesired requests

Original: http://lists.opensips.org/pipermail/users/2013-March/024887.html

A few suggestions (mostly already suggested by many guys in this thread, i
am only arranging their order to a secure setup), opensips log level should
be at least 2.

1. I usually filter out all known nasty users / attackers right in sanity
check section of default request route. My sanity check section structured
something like this,

a). check max forwards.
b). check message size.
c). check user-agent string against filter list, you can use
permissions module for this as well as hard code user-agents as Nick
suggested.

############################################
route {
if (!mf_process_maxfwd_header("10")) {
     sl_send_reply("483","Too Many Hops");
     exit;
};

if (msg:len > max_len) {
     sl_send_reply("513","Message Too Big");
     exit;
};

if ($ua =~ "friendly-scanner") {
     xlog("L_WARN", "[$pr:$fU@$si:$sp]: Rejecting '$rm' request from bogus device '$ua' \n");
     exit;
};
...
#####################################

2. Then in authentication section, i make sure to authenticate both INVITE
and REGISTER requests, you check ret-code for both www-authorize and
proxy-authorize methods and if it is -1 or -2 then do xlog to print log on
intruder which is picked by fail2ban to block the user (make sure text
pattern in your xlog matches failregex in fail2ban! ).

Negative code meanings: http://www.opensips.org/html/docs/modules/2.1.x/auth_db.html#id293676

#####################################
...
if (!www_authorize("","subscriber")) {

     switch ($retcode) {
     case -1:
          xlog("L_NOTICE", "[$pr:$fU@$si:$sp]: Auth error for '$tU' from '$si',
          peer not found - User-Agent: '$ua' \n");
          break;
     case -2:
          xlog("L_NOTICE", "[$pr:$fU@$si:$sp]: Auth error for '$tU' from '$si',
          wrongpassword - User-Agent: '$ua' \n");
          break;
          ...
     };

www_challenge("", "1");
exit;
};
...
#######################################

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