How would I create a custom threat signature that looks for a server's "invalid username" response to a failed login attempt?

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How would I create a custom threat signature that looks for a server's "invalid username" response to a failed login attempt?

Hi,

I'm new to Palo Alto and custom threat signatures. I'm trying to detect invalid login attempts to a web site and apply a time rate. When the user enters an invalid username in the login, the site returns the text "invalid username". Which context would I use to search for this pattern match? I read the "Creating Custom Signatures" document, but it created more questions and I can't seem to find any deeper documentation. By using that document, I was able to use the wordpress brute force combination signature they included (monitoring http POST to wp-login.php), but I have some users that trip those thresholds often because they log into many blogs simultaneously on one server. I'm looking for something a little more granular (not just login attempts (good or bad), but bad attempts based on the site returning the text "bad password", or "invalid username". Is this possible? I don't mind reading more documentation regarding custom signatures if it's available, I've just not seen any other documents yet that give an example like this.

I did take a pcap of the exchange between client and server. I see the text in the pcap, but still not sure which context to use to search for the string. The client sends an http POST to wp-login.php, and then the server issues an http 200 response and then the "Invalid username" text comes a few packets later. Below is the TCP stream from the pcap that contains the "Invalid username" text. I've tried the http_rsp_headers and file_html_body contexts, but still unable to match the text in the exchange.

Thanks!

POST /login/ HTTP/1.1

Host: www.mysite.com

Connection: keep-alive

Content-Length: 164

Cache-Control: max-age=0

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8

Origin: http://www.mysite.com

User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.146 Safari/537.36

Content-Type: application/x-www-form-urlencoded

Referer: http://www.mysite.com/login/

Accept-Encoding: gzip,deflate,sdch

Accept-Language: en-US,en;q=0.8

Cookie: wlp_post_protection=1; PHPSESSID=gh0pdah82shb6les906pc5n4u7; __utma=74238163.586482511.1393824836.1393824836.1393824836.1; __utmc=74238163; __utmz=74238163.1393824836.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); __utma=217530694.1368975606.1393822044.1393822044.1393886113.2; __utmc=217530694; __utmz=217530694.1393822044.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); wfvt_345498598=531583af83045; wordpress_test_cookie=WP+Cookie+check

log=ed&pwd=ed&cptch_result=87Q%3D&cptch_time=1393918888&cptch_number=6&wp-submit=Log+In&redirect_to=http%3A%2F%2Fwww.mysite.com%2Fwp-admin%2F&testcookie=1HTTP/1.1 200 OK

Date: Tue, 04 Mar 2014 07:44:02 GMT

Server: Apache/2.2.15 (CentOS)

X-Powered-By: PHP/5.3.3

Set-Cookie: wfvt_345498598=5315844284ba8; expires=Tue, 04-Mar-2014 08:14:02 GMT; path=/

Expires: Thu, 19 Nov 1981 08:52:00 GMT

Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0

Pragma: no-cache

Set-Cookie: wordpress_test_cookie=WP+Cookie+check; path=/

X-Frame-Options: SAMEORIGIN

Content-Length: 4373

Connection: close

Content-Type: text/html; charset=UTF-8

<!DOCTYPE html>

  <!--[if IE 8]>

  <html xmlns="http://www.w3.org/1999/xhtml" class="ie8" lang="en-US">

  <![endif]-->

  <!--[if !(IE 8) ]><!-->

  <html xmlns="http://www.w3.org/1999/xhtml" lang="en-US">

  <!--<![endif]-->

  <head>

  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />

  <title>mysite www &rsaquo; Log In</title>

  <link rel='stylesheet' id='open-sans-css'  href='//fonts.googleapis.com/css?family=Open+Sans%3A300italic%2C400italic%2C600italic%2C300%2C400%2C600&#038;subset=latin%2Clatin-ext&#038;ver=3.8.1' type='text/css' media='all' />

<link rel='stylesheet' id='dashicons-css'  href='http://www.mysite.com/wp-includes/css/dashicons.min.css?ver=3.8.1' type='text/css' media='all' />

<link rel='stylesheet' id='wp-admin-css'  href='http://www.mysite.com/wp-admin/css/wp-admin.min.css?ver=3.8.1' type='text/css' media='all' />

<link rel='stylesheet' id='buttons-css'  href='http://www.mysite.com/wp-includes/css/buttons.min.css?ver=3.8.1' type='text/css' media='all' />

<link rel='stylesheet' id='colors-fresh-css'  href='http://www.mysite.com/wp-admin/css/colors.min.css?ver=3.8.1' type='text/css' media='all' />

<!--[if lte IE 7]>

<link rel='stylesheet' id='ie-css'  href='http://www.mysite.com/wp-admin/css/ie.min.css?ver=3.8.1' type='text/css' media='all' />

<![endif]-->

<meta name='robots' content='noindex,follow' />

<script type="text/javascript">

addLoadEvent = function(func){if(typeof jQuery!="undefined")jQuery(document).ready(func);else if(typeof wpOnload!='function'){wpOnload=func;}else{var oldonload=wpOnload;wpOnload=function(){oldonload();func();}}};

function s(id,pos){g(id).left=pos+'px';}

function g(id){return document.getElementById(id).style;}

function shake(id,a,d){c=a.shift();s(id,c);if(a.length>0){setTimeout(function(){shake(id,a,d);},d);}else{try{g(id).position='static';wp_attempt_focus();}catch(e){}}}

addLoadEvent(function(){ var p=new Array(15,30,15,0,-15,-30,-15,0);p=p.concat(p.concat(p));var i=document.forms[0].id;g(i).position='relative';shake(i,p,20);});

</script>

  </head>

  <body class="login login-action-login wp-core-ui">

  <div id="login">

  <h1><a href="http://wordpress.org/" title="Powered by WordPress">mysite www</a></h1>

  <div id="login_error"> <strong>ERROR</strong>: Invalid username. <a href="http://www.mysite.com/login/?action=lostpassword" title="Password Lost and Found">Lost your password</a>?<br />

</div>

<form name="loginform" id="loginform" action="http://www.mysite.com/login/" method="post">

  <p>

  <label for="user_login">Username<br />

  <input type="text" name="log" id="user_login" class="input" value="" size="20" /></label>

  </p>

  <p>

  <label for="user_pass">Password<br />

  <input type="password" name="pwd" id="user_pass" class="input" value="" size="20" /></label>

  </p>

  <p class="cptch_block"><br /> <input type="hidden" name="cptch_result" value="hIE=" />

  <input type="hidden" name="cptch_time" value="1393919042" />

  <input type="hidden" value="Version: 2.4" />

  1 &#43; on&#101; =  <input id="cptch_input" type="text" autocomplete="off" name="cptch_number" value="" maxlength="2" size="2" aria-required="true" required="required" style="margin-bottom:0;display:inline;font-size: 12px;width: 40px;" /> </p>

  <br /> <p class="forgetmenot"><label for="rememberme"><input name="rememberme" type="checkbox" id="rememberme" value="forever"  /> Remember Me</label></p>

  <p class="submit">

  <input type="submit" name="wp-submit" id="wp-submit" class="button button-primary button-large" value="Log In" />

  <input type="hidden" name="redirect_to" value="http://www.mysite.com/wp-admin/" />

  <input type="hidden" name="testcookie" value="1" />

  </p>

</form>

<p id="nav">

  <a href="http://www.mysite.com/login/?action=lostpassword" title="Password Lost and Found">Lost your password?</a>

</p>

<script type="text/javascript">

function wp_attempt_focus(){

setTimeout( function(){ try{

d = document.getElementById('user_login');

if( d.value != '' )

d.value = '';

d.focus();

d.select();

} catch(e){}

}, 200);

}

if(typeof wpOnload=='function')wpOnload();

</script>

  <p id="backtoblog"><a href="http://www.mysite.com/" title="Are you lost?">&larr; Back to mysite www</a></p>

  </div>

  <div class="clear"></div>

  </body>

  </html>

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