Malware Detection (the PHP File Scanner)

[Note]Note

This feature is only available in the for-a-fee Professional release of our software.

Malware detection

Admin Tools has a very powerful feature called PHP File Change Scanner. This feature can be used to perform a security scan of the PHP files included anywhere under your site's root directory, as well as detect any modified or added files in subsequent runs. The file scanning engine is built on top of Akeeba Engine, the engine powering our acclaimed Akeeba Backup site backup software, ensuring rock solid operation. Each scanned file also comes with a preliminary automatic security assessment ("threat score") which can give you a quick idea of how possible it is that the file in question could be suspicious (malware / hacked file).

The PHP File Change Scanner has more handy features. For example the ability to produce DIFF's (a synopsis of how modified files differ from the previous known copy), print and export the scan reports as well as the interactive report viewer which allows you to peek at the contents of each file. This feature can allow power users to detect and eliminate hacks much faster than using a purely manual method. You can also automate the run of the scanner engine using a CLI CRON job, making sure that you always know what's going on with your site.

[Warning]Warning

By default, only files with a lowercase .php, .phps, .php3 and .inc extension are scanned. Non-PHP files or PHP files whose extension is different (e.g. .PHP in capitals, .php4, .php5, .php7 and so on) will not be scanned unless you configure it so. The idea of this feature is to scan only PHP files, because the modification or addition thereof could signify a potential problem or hack of your site. We only use a subset of lowercase extensions because these are the extensions of virtually all PHP files you will encounter on the overwhelming majority of sites. Other extensions are host-specific and not universal enough to guarantee that they do contain PHP code.

Moreover, not all hacking scripts are written in PHP. Some of them may be written in PERL, Python, Ruby, shell script (e.g. Bash) or they could be executable binaries. Some hackers may also place infected PDFs, PNGs, Word documents etc which will infect your computer if you open them. None of those files will be scanned by Admin Tools's PHP File Change Scanner. These files can only be detected by using a traditional antivirus.

How does it work and what should I know?

The PHP File Change Scanner is a hybrid between a backup engine and a file scanner. It works by "sweeping" your WordPress site for PHP files and comparing them to their last known state saved in the database. It will then report any changes, i.e. files which have been modified or added since the previous scan. The following paragraphs will explain how some aspects of the file scanning and reporting engine work.

Scope of the scan. Only files inside your WordPress site's root are scanned. If you have placed PHP files outside of your site's root, they will not be scanned. Moreover, any readable directory under your site's root will be scanned, even if it does not belong to the current WordPress installation. For example, if you have additional sites or subdomains stored in subdirectories of your site's root, they will be scanned nonetheless.

Only PHP files are scanned. Only files with the extensions defined in the Scanner Preferences page are scanned. By default this is .php, .phps, .php3 and .inc files. Non-PHP files or PHP files whose extension is different will not be scanned. The idea of this feature is to scan only PHP files, because the modification or addition thereof could signify a potential problem or hack of your site. We only use the lowercase .php extension because this is the extension of virtually all PHP files and the other extensions are host-specific and not universal enough to guarantee that they do contain PHP code.

File comparison terms. In order to determine if a file is modified, Admin Tools will compare its size, last modification time and md5 sum. If any of these do not match the previous scan's results, the file is considered modified. If there is no record of that file in a previous scan, the file is considered as new.

When a file change is detected. A file change is detected only if the file is added or modified since the immediately previous scan. This means that if you scan now, modify a PHP file and scan again, it will show up as modified. If you perform a third scan right after the second one, the file will NOT be reported as changed (unless it has a non-zero Threat Score and it's not Marked as Safe). This is normal. The file was changed between the first and second scan, but not between the second and third scan.

Threat score calculation. Whenever Admin Tools Professional encounters a new or modified file, it calculates a "threat score". This is a weighed sum of potential security "red flags". Essentially, Admin Tools Professional runs a few heuristics against the PHP file in question, looking for code patterns which are commonly (but NOT NECESSARILY) used in hacking scripts and hacked files. Each of those patterns is assigned a "weight". The weight is multiplied by the number of occurrences of the pattern to give a score. The sum of these scores is what we call a "threat score". How to interpret it: the higher the threat score, the more probable it is that this could be a nefarious file and its contents should be manually assessed.

Please note that a high threat score does not necessarily mean that the file is hacked or malware. Likewise, a low but non-zero threat score (1-10) does not necessarily mean that the file in question is necessarily safe. Please take a look at the next few sections for more information.

Removing old scans has some consequences. When you remove an old scan, Admin Tools also removes all associated file alert records. If you have defined some files with a non-zero Threat Score as "Marked Safe" in this scan's report, then this information is lost when you delete this scan. As a result, subsequent scans will, again, report the file as "Suspicious".

Heavy database usage. In order for this feature to work, Admin Tools Professional needs to perform very heavy use of your database. There will be at least one database query for each and every PHP file on your site. The average site contains over 1,000 such files. Moreover, there will be one database query for each and every new or modified file.

Heavy resource usage. Scanning your site is a very CPU and memory intensive procedure. Admin Tools Professional has to scan your entire site, find the PHP files, read them, calculate an MD5 sum (very CPU and memory intensive process!), read data from the database, compare it with those in memory, write data to the database and repeat that for each file. This does put a big strain on your server, similar to what you get when you're backing up your site.

Potential problems. As stated above, the file scan operation is very database, CPU and memory intensive. This can cause failure of the scan process due to one of several reasons, especially on lower-end hosts (usually: cheap or low quality shared hosts):

  • Memory exhaustion. Getting an out-of-memory error is not at all unlikely. We strongly recommend having at the very least 32Mb of available PHP memory. We recommend 64Mb to 128Mb for trouble-free operation. If you only have 16Mb or less of available PHP memory, the scan will most likely fail.

  • Exhausting your MySQL query limit. Some hosts have a limit on how many queries you can run per minute or per hour. Because the file scan is very database-intensive, you may exhaust this limit, causing the scan to crash.

  • MySQL server has gone away. Likewise, some hosts have set up MySQL (the database server) to forcibly close the connection if it doesn't receive data for a short time period, usually anything between 0.5 and 3 seconds. This could cause the infamous "MySQL server has gone away" error message, killing your scan.

  • Timeout. Calculating MD5 and diffs for large files is a very time consuming process. It is possible that PHP times out during that operation, especially on slow, low-end hosts.

  • Hitting the CPU usage limit. Many hosts enforce a CPU usage limit. Given that the file scan is a very CPU-intensive process, it is possible that you hit that limit. What usually happens is that the host kills the script causing the "excessive" CPU usage (our file scan operation).

All of the above manifest themselves as a 500 Internal Server Error message or a never ending scan process when trying to scan your site. Unfortunately, these are all server limitations and we can not work around them, while maintaining the usefulness of the PHP File Change Scanner feature. If you hit on those limitations, our recommendation is to switch to a better performing / higher-quality host.

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