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We run a shared hosting webserver with the usual LAMP stack. It is up and running since many years ago (uhm, Apache-1.3 and PHP-3 days?) and went through many iterations. We strive to have good sysadmin policies, like keeping all the stack up-to-date, checking for weak passwords, minimizing the attack surface, using suhosin, keeping an eye on systems logs, and so on. Of course every virtual host is confined to its directory (both for FTP access and as php open_basedir).

But at the end of the day it's always a webserver running untrusted PHP crap uploaded by customers (read: unknown and mostly-stupid users without any IT experience) with HTTP exposed to the world (web forms and whatnot)... these scenarios are not too uncommon:

  • user gives its password to too many people and its site gets compromised
  • user's PC gets compromised and the FTP / web app / whatever password stolen from there
  • user installs crappy PHP stuff and it gets compromised
  • user installs good PHP stuff (does it even exists?) but doesn't update in years and it gets compromised
  • user writes its own PHP stuff (ARGH! they're coming outta the ---------- walls!)
  • and so on. you got the idea.

When investigating compromised PHP/JS/HTML/whatever stuff we sometimes find malware in the form of javascript (either in .js files or embedded in html stuff) and sometimes we even find .zip files with malware/viruses for Microsoft Windows inside.

With such a wild environment it is not possible to repeatedly run automated vulnerability tests on the web sites, and probably it wouldn't be much useful either. I'm also thinking stuff like mod_security would be out of question in such a shared, generic, out of control environment.

But I'm wondering if there is anything antivirus-like that we could run server-side, at least to look for web sites compromised with well known javascript or executable stuff, or known vulnerabilities in old versions of PHP web apps. Something to run from cron every night and get a nice email report.

Is there such a thing? Could clamav detect some of those nasty JS stuff? (I'm assuming we can already use it to detect uploaded zip files with Win32 malware) Anything else I hadn't thought of that could be run server-side for a static scan? And what about content stored in MySQL (eg. javascript uploaded from forms and stored in SQL for later display on web pages)?

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4 Answers

Snort can detect while the malware is being uploaded. Also, use Cloud Linux or SELinux etc. This prevents many works from compromising the site, if configured to do so. You can run Kaspersky Scan on the web server too, it detects some things, but not always disinfect it properly. Above all, you can implement policy the way, that anything uploaded has to be with restricted access, as well what you can do, is to prevent overwriting the files except for the special folders, which cannot be linked externally. This is possible and there are many ways of doing it. ACLs, SELinux, SUEXEC etc.

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mod_security modsecurity.org can also be a great help. –  Janne Pikkarainen Jul 11 '12 at 16:51
    
While they're all useful stuff, none of them is a static scanner, which the question is about. Also, I think not all of them are applicable to a many-vhosts-low-cost-shared-hosting environment. I understand "Kaspersky Scan" as the "Kaspersky Security Scan" free tool, that's not even applicable to a LAMP server (does not run on Linux). –  Luke404 Jul 11 '12 at 17:02
    
Cloud Linux applies ultimately to low cost shared hosting, this is what is was designed for, same as SELinux. Kaspersky has antivirus product, which performs scan and it has the best detection ratio while clamav has the lowest. Snort can apply to the complete network, and it's the must-have for any network. –  Andrew Smith Jul 11 '12 at 20:04
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Clam AntiVirus is the tool you want. It sees common duty in mail systems, but there's no reason you couldn't monitor the uploads that come in through your web application.

Just remember that you'll probably need changes to application code to use this effectively. It will need to deal with the fact that ClamAV will scan, detect, and possibly remove/obstruct files independently of your application. The best option would be to call ClamAV from your application for each upload, but that may be more development time than you'd like to invest.

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In addition to ClamAV, consider using Maldet for additional malware detection. According to the docs, it has the ability to integrate with ClamAV, though I haven't personally set this up.

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I recommend you to try using Linux Malware Detect (http://www.rfxn.com/projects/linux-malware-detect/). Put it to cron to run periodic scans:

0 * * * * /usr/local/sbin/maldet -r ~ >output

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