Script Shell de détection des logiciels malveillants et des portes dérobées

You ask about 3 different things...

1. Root kits;
2. Backdoors;
3. Malware.

Root kits

Most root kits use the kernel to hide themselves and they are only visible from within the kernel.

If you want to know how to find them why not use the power of open source and install rkhunter and see how they do it? You can find the source here.

Besides that CERT has a thorough explanation on what to look for when dealing with root kits. Highlights from the link:

• Examine log files for connections from unusual locations or other unusual activity

• Look for setuid and setgid files (especially setuid root files) everywhere on your system

  find / -user root -perm -4000 -print
  find / -group kmem -perm -2000 -print
  

• Check your system binaries to make sure that they haven't been altered.

• Examine all the files that are run by 'cron' and 'at.'
• Check for unauthorized services.
• Examine the /etc/passwd file on the system and check for modifications to that file.
• Check your system and network configuration files for unauthorized entries.
• Look everywhere on the system for unusual or hidden files (files that start with a period and are normally not shown by 'ls').

Most of these you can do from command line.

Also worth reading:

• https://serverfault.com/questions/158691/how-to-check-if-a-linux-server-is-clean-from-rootkits-backdoors-botnets-etc

Backdoors

The problem with backdoors is that they generally are flaws in software that get abused. The basic set of rules...

1. immediately install security updates when you're notified;
2. do not install antivirus, as you really don't need it in Linux; unless you share files with Windows
3. enable the firewall (sudo ufw enable) without further tweaks;
4. stick to the official repo's as much as possible, and only deviate from them when strictly necessary and with much caution;
5. keep Java (both openJDK and Oracle Java) disabled by default in your browser, and only enable it when needed;
6. use Wine with caution;
7. and most important of all: use your common sense. The biggest security threat is generally found between keyboard and chair.

Worth reading:

• What to do regarding BackDoor.Wirenet.1
• https://serverfault.com/questions/171893/how-do-you-search-for-backdoors-from-the-previous-it-person
• https://stackoverflow.com/questions/9417739/how-to-find-out-backdoor-in-php-source-code
• https://security.stackexchange.com/questions/35944/how-can-i-find-the-malicious-backdoor-codes-without-knowing-the-last-modified-da
• https://security.stackexchange.com/questions/32645/how-can-i-detect-backdoors

Malware

Scan /etc/hosts for weird IP adresses and host names. If you look at these:

• Google.com redirect malware on FF
• Ubuntu vulnerable to malware sites?
• Popup Malware “openadserving.com”
• Chrome Popup Malware "openadserving.com"?

either a browser extension or an alteration to /etc/hosts is the cause.

Also a good read is:

• Where can I look for malware that may have been installed on my machine?