How can network security professionals determine if a file is malicious? (2024)

One of the first steps to determine if a file is malicious is to check its properties. You can use a file manager or a command-line tool to examine the file name, extension, size, date, attributes, and permissions. Sometimes, malicious files can have misleading names or extensions that try to trick you into opening them. For example, a file named invoice.pdf.exe may look like a PDF document, but it is actually an executable file that can run malicious code. You can also look for hidden or system files that may have been created or modified by malware. Additionally, you can use a tool like file or strings to inspect the file content and type.

Another way to determine if a file is malicious is to calculate its hash value. A hash value is a unique identifier that is generated from the file content using a mathematical function. You can use a tool like md5sum or sha1sum to compute the hash value of a file. Then, you can compare the hash value with a known database of malicious or benign files, such as VirusTotal or the National Software Reference Library. If the hash value matches a known malicious file, you can conclude that the file is malicious. However, if the hash value does not match any known file, you may need to perform further analysis.

A file signature is a sequence of bytes that can indicate the format or origin of a file. You can use a tool like sigcheck or peid to scan the file for signatures and extract information such as the file type, version, publisher, and certificate. File signatures can help you determine if a file is malicious by revealing if it has been tampered with, if it has been signed by a trusted or untrusted source, or if it has any anomalies or inconsistencies. For example, a file that claims to be a JPEG image but has a signature of an executable file may be suspicious.

The most definitive way to determine if a file is malicious is to observe its behavior when it is executed. You can use a tool like procmon or sysinternals to monitor the file activity and see what processes, files, registry keys, network connections, or other resources it accesses or modifies. You can also use a tool like wireshark or tcpdump to capture the network traffic and analyze the packets and protocols that the file uses. File behavior can help you determine if a file is malicious by showing if it performs any malicious actions, such as deleting or encrypting files, creating backdoors, stealing data, or connecting to malicious servers.

To perform the techniques described above, you will need some file analysis tools. There are many tools available, both free and paid, that can suit different needs and preferences. VirusTotal is a web-based service that scans files and URLs with multiple antivirus engines and provides reports on their detection and reputation. Cuckoo Sandbox is an open-source software that creates isolated environments where you can run and analyze files and observe their behavior and impact. IDA Pro is a commercial software that disassembles and debugs files, while Ghidra is a free software developed by the National Security Agency that performs similar functions. OllyDbg is another free software that debugs and modifies files, allowing you to manipulate their execution and memory.

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

Network Security

+ Follow

Thanks for your feedback

Your feedback is private. Like or react to bring the conversation to your network.