Beware WARMCOOKIE Backdoor Knocking Your Inbox

WARMCOOKIE is a new Windows backdoor that is deployed by a phishing effort with a recruiting theme dubbed REF6127.

The WARMCOOKIE backdoor can be used to take screenshots of the target computer, deliver additional payloads, and fingerprint a system.

“This malware represents a formidable threat that provides the capability to access target environments and push additional types of malware down to victims”, Elastic Security Labs shared with Cyber Security News.

WARMCOOKIE Execution Flow

Researchers have been observing phishing efforts that use lures associated with recruitment firms since late April 2024.

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By addressing recipients by name and their present employer, these emails enticed them to look for new employment by clicking on a link that would take them to an internal system where they could read a job description.

After clicking, users are taken to a landing page that appears to be an authentic website that was created only for them. 

There, they must complete a CAPTCHA test to download a document. The landing pages, which mention a new variation of URSNIF, are similar to earlier campaigns that Google Cloud’s security team has identified.

When the CAPTCHA is solved, an obfuscated JavaScript file is downloaded from the page. This obfuscated script launches PowerShell, initiating the initial task to load WARMCOOKIE.

The PowerShell script uses the Background Intelligent Transfer Service (BITS) to download WARMCOOKIE and launch the DLL. 

Researchers note that 45.9.74[.]135 is the IP address where the threat actor continuously and swiftly creates new landing pages.

The actor made an effort to target several hiring agencies while combining industry-related keywords.

The backdoor gathers the following values before sending its first outgoing network request, and they are used to identify and fingerprint the target system.

• Volume serial number
• DNS domain of the victim machine
• Computer name
• Username

In particular, the malware that can take screenshots from victims’ computers offers a variety of harmful possibilities, like making use of private data that is visible on the screen or keeping a close eye on the victim’s computer. 

According to analysts, threat actors create new infrastructure and domains every week to support these campaigns.

“While there is room for improvement on the malware development side, we believe these minor issues will be addressed over time,” researchers conclude.

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