trojan horse in the shape of twigs

QBot changes tactic, remains a menace to business networks

QBot, an infostealer-turned-dropper that aids criminal gangs in their malicious campaigns, is now being distributed as part of a phishing campaign using PDFs and Windows Script Files (WSF), according to recent discoveries by malware hunter Proxylife (@pr0xylife) and the Cryptolaemus group (@Cryptolaemus1).

The last time QBot (aka QakBot) had its modus operandi changed was in November. Campaign operators adopted tactics from Magniber’s playbook to successfully exploit a Mark of the Web (MotW) zero-day flaw to run a JavaScript (JS) that executed QBot.

The latest QBot phishing campaign is illustrated simply in the diagram below:

The QBot campaign illustrated (Source: Jerome Segura | Malwarebytes Labs)

The attack starts with a reply-chain phishing email, when threat actors reply to a chain of emails with a malicious link or attachment. BleepingComputer has noted that these phishing emails use a variety of languages. This means the language barrier is absent in such an attack, so any business from any part of the world could be affected.

A sample reply-chain phishing email in French, carrying a PDF attachment disguised as a cancellation letter. (Source: BleepingComputer)

Once someone in the email chain opens the attached PDF, they see a message saying, “This document contains protected files, to display them, click on the ‘open’ button.” Clicking the button downloads a ZIP file containing the WSF script.

The heavily obfuscated script contains a mix of JS and VBScript code that, when run, triggers a PowerShell that then downloads the QBot DLL from a list of hardcoded URLs. This script tries each URL until a file is downloaded to the Windows Temp folder (%TEMP%) and executed.

Once QBot runs, it issues a PING command to check for an internet connection. It then injects itself into wermgr.exe, a legitimate Windows Error Manager program, to run quietly in the background.

Because QBot is said to be used by operators of ransomware-as-a-service (RaaS) offerings, its presence in company systems could be disastrous. Therefore, any organization must take its QBot-infected systems offline as soon as possible and thoroughly scan and review network logs for unusual behavior.

The DFIR Report in February 2022 showed QBot collecting data from a compromised system 30 minutes after infecting it. Within an hour, QBot can be spread to adjacent systems.

Malwarebytes detects the malicious DLL (QBot).

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