Malware Analysis

[introduction]

Forensics CheatSheets​

https://www.jaiminton.com/cheatsheet/DFIR/#

Online Services​

• • VirusTotal
  • HybridAnalysis
  • Koodous
  • Intezer

Offline Antivirus and Detection Tools​

Yara​

Install​

sudo apt-get install -y yara

Prepare rules​

Use this script to download and merge all the yara malware rules from github: https://gist.github.com/andreafortuna/29c6ea48adf3d45a979a78763cdc7ce9 Create the rules directory and execute it. This will create a file called malware_rules.yar which contains all the yara rules for malware.

wget https://gist.githubusercontent.com/...3bed1f786b26a0654aa2f31/malware_yara_rules.py

mkdir rules

python malware_yara_rules.py

Scan​

yara -w malware_rules.yar image #Scan 1 file

yara -w malware_rules.yar folder #Scan the whole folder

YaraGen: Check for malware and Create rules​

You can use the tool YaraGen to generate yara rules from a binary. Check out these tutorials: Part 1, Part 2, Part 3

python3 yarGen.py --update

python3.exe yarGen.py --excludegood -m ../../mals/

ClamAV​

Install​

sudo apt-get install -y clamav

Scan​

sudo freshclam #Update rules

clamscan filepath #Scan 1 file

clamscan folderpath #Scan the whole folder

IOCs​

IOC means Indicator Of Compromise. An IOC is a set of conditions that identify some potentially unwanted software or confirmed malware. Blue Teams use this kind of definition to search for this kind of malicious files in their systems and networks. To share these definitions is very useful as when malware is identified in a computer and an IOC for that malware is created, other Blue Teams can use it to identify the malware faster.
A tool to create or modify IOCs is IOC Editor. You can use tools such as Redline to search for defined IOCs in a device.

Loki​

Loki is a scanner for Simple Indicators of Compromise. Detection is based on four detection methods:

1. File Name IOC

Regex match on full file path/name



2. Yara Rule Check

Yara signature matches on file data and process memory



3. Hash Check

Compares known malicious hashes (MD5, SHA1, SHA256) with scanned files



4. C2 Back Connect Check

Compares process connection endpoints with C2 IOCs (new since version v.10)

Linux Malware Detect​

Linux Malware Detect (LMD) is a malware scanner for Linux released under the GNU GPLv2 license, that is designed around the threats faced in shared hosted environments. It uses threat data from network edge intrusion detection systems to extract malware that is actively being used in attacks and generates signatures for detection. In addition, threat data is also derived from user submissions with the LMD checkout feature and malware community resources.

rkhunter​

Tools like rkhunter can be used to check the filesystem for possible rootkits and malware.

sudo ./rkhunter --check -r / -l /tmp/rkhunter.log [--report-warnings-only] [--skip-keypress]

PEpper​

PEpper checks some basic stuff inside the executable (binary data, entropy, URLs and IPs, some yara rules).

NeoPI​

NeoPI is a Python script that uses a variety of statistical methods to detect obfuscated and encrypted content within text/script files. The intended purpose of NeoPI is to aid in the detection of hidden web shell code.

php-malware-finder​

PHP-malware-finder does its very best to detect obfuscated/dodgy code as well as files using PHP functions often used in malwares/webshells.

Apple Binary Signatures​

When checking some malware sample you should always check the signature of the binary as the developer that signed it may be already related with malware.

#Get signer

codesign -vv -d /bin/ls 2>&1 | grep -E "Authority|TeamIdentifier"



#Check if the app’s contents have been modified

codesign --verify --verbose /Applications/Safari.app



#Check if the signature is valid

spctl --assess --verbose /Applications/Safari.app

Detection Techniques​

File Stacking​

If you know that some folder containing the files of a web server was last updated on some date. Check the date all the files in the web server were created and modified and if any date is suspicious, check that file.

Baselines​

If the files of a folder shouldn't have been modified, you can calculate the hash of the original files of the folder and compare them with the current ones. Anything modified will be suspicious.

Statistical Analysis​

When the information is saved in logs you can check statistics like how many times each file of a web server was accessed as a web shell might be one of the most.

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