Friday, 22 January 2016

Quick HTACCESS Rules and VBS / ASP Functions for Banning Hackers

Quick HTACCESS Rules and VBS / ASP Functions for Banning Hackers

By Strictly-Software

Having to work on some old sites sometimes means that the security is often pretty lax and even if the system is locked down to prevent SQL Injection by having proper permissions, e.g not allowing CUD (Create, Update, Delete) statements to run from the front end, there is still the possibility of XSS hacks on an old ASP Classic site.

Running an exploit scanning tool like the OWASP ZAP tool is a good idea to find possible holes but even then I have found that it doesn't find all possible exploits. There are hackers looking to harm you and then there are the "ethical hackers" who will still try and probe your site to "warn you", and the "unethical" sort who try to blackmail customers by putting your URLS up on special websites that claim the site is a security minefield.

Even if your browser protects you from most cases, e.g trying to find a recent hack in Chrome was a nightmare due to it automatically protecting me by changing the HTML source, these reputation attacks will hurt your company and customers. Therefore even if you are not given the time or cannot fix every hole that could exist in your system, you should do as much as possible to prevent them from being found in the first place.

Having a proper WAF (Web Application Firewall), is always recommended but even if you don't you can make use of your .htaccess file to block a lot of probing plus you can always use code to validate requests, such as form submissions on contact forms or other pages that accept user content.

Having a CAPTCHA is always a good idea, and if not use a BOT TRAP if at all possible, however this won't stop a human with the spare time to examine your source code and work out what is going on to get around it either manually or by writing a custom BOT.


There are many .HTACCESS rules you can use to block attacks but I have found that some are overly obtrusive and will block legitimate requests.

For example if you want a good list of possible .htaccess rules to prevent probes from PHP, JavaScript, MySQL and WordPress then downloading the free plugin WP Security is a good way to see the sort of rules that can be applied to an .htaccess file.

Just turn on all the firewall, image hot linking and file protection rules you want and then go and view the .htaccess file in your root folder.

These rules are quite comprehensive and most are generic enough to be copied and used on Microsoft platforms that support .htaccess files if you want. Obviously a PHP hack isn't going to work on an IIS server but if you want to still catch people trying these hacks then having a page that logs and bans them if possible is an idea.

I won't show you all the rules you can take from other plugins but I will show you some core rules that can cut down your "Bad Traffic" by a huge percentage.

I have found on my own sites that banning any Internet Explorer version under 7 is always a good idea as many of these hacker tools that script kiddies use, still have a default user-agent of IE 5-6, and for some reason these people don't bother changing the user-agent.

Therefore just examining your IIS log files for any user with IE 5, 5.5 or 6 user-agent is a good indication that they are up to no good. You can read about this and another way to reduce bandwidth on another article of mine here.

RewriteRule %{HTTP_USER_AGENT} (MSIE\s6\.0|MSIE\s5\.0|MSIE\s5\.5) [NC]
RewriteRule .* [L,R=302]

This rule sends any user-agent with IE 5, 5.5 or 6 back to the localhost on the users machine with a 302 rewrite rule. 

You could just use a [F] Forbidden (403) rule if you want but at least this way you are going to piss the offenders off a bit more by sending them in circles.

Here are some more rules I use regularly which sends the user to a special hack.asp page where I can log their details and bounce them to a honeypot or a circular link maze of my choice.

As you can see the rules cover some common SQL Injection attacks that utilize the system tables, anything trying to be executed (EXEC), plus <Script> tags using standard and URL encoded brackets.

This is because a lot of "ethical hackers" or probers will try simple <script>alert("Hacked")<script> tests on any search form they can find on your site.

If the page you get posted to pops up an alert box then you are vulnerable to Cross Site Scripting attacks.

Other methods they commonly use are HTML tags that allow for onload functions to be run as well as "break out" code that tries to close an HTML element, then output it's own HTML or JavaScript code.

RewriteRule ^/.*?\.asp\?(.*?DECLARE[^a-z]+\@\w+[^a-z]+N?VARCHAR\((?:\d{1,4}|max)\).*)$ /jobboard/error-pages/hack\.asp\?$1 [NC,L,U]
RewriteRule ^/.*?\.asp\?(.*?sys.?(?:objects|columns|tables).*)$ /jobboard/error-pages/hack\.asp\?$1 [NC,L,U]
RewriteRule ^/.*?\.asp\?(.*?;EXEC\(\@\w+\);?.*)$ /jobboard/error-pages/hack\.asp\?$1 [NC,L,U]
RewriteRule ^/.*?\.asp\?(.*?(%3C|<)/?script(%3E|>).*)$ /jobboard/error-pages/hack\.asp\?$1    [NC,L,U]
RewriteRule ^/.*?\.asp\?(.*?((%2[27])%3E(%20)*%3C|['"]>\s*<).*)$ /jobboard/error-pages/hack\.asp\?$1    [NC,L,U]
RewriteRule ^/.*?\.asp\?(.*?(<svg|alert\(|eval\(|onload).*)$ /jobboard/error-pages/hack\.asp\?$1    [NC,L,U]

# Block blank or very short user-agents. If they cannot be bothered to tell me who they are or provide jibberish then they are not welcome!                                                       
RewriteCond %{HTTP_USER_AGENT} ^(?:-?|[a-z1-9\-\_]{1,10})$ [NC]
RewriteRule .* - [F,L]

ASP / VBScript Function

As well as having a good set of .htaccess rules to prevent hacks by QueryString you can always use a function to parse any content through to look for hacks. Of course it is possible to use .htaccess rules to filter out HTTP POST and GET Requests but you may want to prevent too many regular expressions running on every POST with your .HTACCESS file by just passing publicly accessible forms with your function.

A very basic example is below.

Function TestXSS(strVal)
 Dim bRet : bRet = False

 '* remove encoded < > etc, use your own URL Decode function, I use a SERVER SIDE JavaScript with their decodeURIComponent function to do this in ASP Classic
 strVal = URLDecode(Trim(strVal))

 '* URL Encoded stuff like %3Cscript%3Ealert(1)%3C%2fscript%3E will get trapped by ISAPI
 '* RegTest is just a generic function I have which does a regular expression test against a value and pattern to see if it matches like C# RegEx.IsMatch
 If RegTest(strVal, "(?:<\/?script(\s|>|)|\W+eval\(|\W+(?:src|onload)=|document\.)") Then
  bRet = True
  If RegTest(strVal, "(';|"";|'>|"">|alert\(|document\.cookie|\.frame|\.top\.location|(?:document|location)\.src|on\w+\()") Then
   bRet = True
   bRet = False 
  End If
 End If

 TestXSS = bRet
End Function

Obviously you can extend this function as much as you want to check for other words or pieces of code that shouldn't be passed around in forms or querystrings. It is just a base for you to start with.


Remember security is best approached in a multi layered way without your system relying on one form of defence alone.

WAFS, HTACCESS rules, code, CAPTCHAS, BOT Traps, special "not to be visited" links in your Robots.txt file that then send visitors to that page off to honeypots for breaking the rules, rude word lists, proper file permissions and HTTP parameter checks are all various ways to protect your site.

However many of these are sticking plasters which are used to protect your code in case it has not been 100% written to sanitise ALL user input, escape content outputted to the page, or has incorrect database security permissions.

Having a properly written and secured system is always the best solution however new exploits are always coming out so having as much protection as possible is not only good for security but it can save on bandwidth costs as well!

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