Hackers use the Sign of the Internet to deliver malware

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The attackers bypass the Windows protection feature and download QBot and Cobalt Strike.

Cybersecurity researcher ProxyLife has discovered that new phishing attacks exploit a Windows zero-day vulnerability that delivers Qbot malware bypassing Mark of the Web protections.

When files are downloaded from an untrusted source, such as the Internet or an email attachment, Windows adds a special attribute to the file called Mark of the Web (MoTW). When a user tries to open a file with the MoTW attribute, Windows displays a security warning:

In a new QBot phishing campaign, hackers exploit the Mark of the Web 0-day vulnerability by spreading JS files signed with garbled signatures. The campaign starts with an email containing a link to the document and a password to the file.

Clicking the link downloads a password-protected ZIP archive containing another ZIP file containing an IMG file that Windows automatically mounts as a new drive. IMG file contains the following files:

The JavaScript file contains a VBScript script that reads the "data.txt" file and adds some code to load the "port/resemblance.tmp" DLL file.

Because the JS file is signed with the malformed key that was used in the Magniber campaigns to exploit the Windows 0-day vulnerability, the JS script loads QBot without displaying MoTW warnings. In addition, the QBot malware DLL is loaded into legitimate Windows processes to avoid detection, such as "wermgr.exe" or "AtBroker.exe".

Microsoft has been aware of this vulnerability since October. Now that other malware campaigns are using it, the expert hopes the bug will be fixed as part of security updates in December 2022.

Once downloaded, QBot (Qakbot) steals emails in the background to be used in other phishing attacks or to install additional payloads such as Brute Ratel, Cobalt Strike and other malware.