Threat actors do not use .7z formats by accident. The format relies heavily on the , which provides incredibly high compression ratios. This architectural benefit is turned into a security vulnerability through several exploitation styles:
Inside, it contains executable files ( .exe ), scripts ( .vbs , .js , .ps1 ), or malicious documents ( .docm , .xlsm ) that download or run malware. Why Use 7z? Attackers prefer using 7z files for several reasons:
The user saves and attempts to open the archive. They may be prompted for a password provided in the email.
: If you are curious about its contents without opening it, you can upload the file to VirusTotal to see what security vendors have flagged inside. malignant.7z
Simply opening the archive to "look" is generally safe, but extracting or running any file inside can trigger an infection. Use a Sandbox: Researchers analyze files like malignant.7z
: It may contain files related to the 2021 film Malignant , such as a compressed version of the movie, promotional assets, or soundtrack.
Malignant.7z: Inside the Deceptive Evolution of Archive-Based Malware Threat actors do not use
Re-packaged versions of popular software that look identical to the original but execute a background "Trojan" once run. Script-Based Malware: Files with extensions like that execute commands directly in the Windows environment. Executable Payloads:
The core of the trick lies in the , a small part of the file that tells a program how to handle the data inside it, including whether the data is stored as raw, uncompressed bytes ( Method 0 ) or compressed using the standard DEFLATE algorithm ( Method 8 ). Most antivirus engines will trust this header and scan the file's contents according to what it says. Zombie ZIP works by maliciously altering the header in the following way:
The is a crucial security feature in Windows. It's an invisible tag that Windows adds to any file downloaded from the internet or an email attachment (ZoneId 3 or 4). When a user tries to run a file with the MotW tag, Windows displays a security warning prompt, giving the user a chance to reconsider. If an archive file contains malicious files but is missing this MotW tag, Windows may not issue any warning at all, giving the attacker a significant advantage. Why Use 7z
To remain protected, users should always ensure they are running the latest version of 7-Zip (Version 25.00 or higher) and only download from the official source.
Unmasking the Threat: The Mechanics, Risks, and Analysis of Malicious 7z Archives