Behind the CAPTCHA: A Intelligent Gateway of Malware

Authored by Yashvi Shah and Aayush Tyagi

Government abstract

McAfee Labs just lately noticed an an infection chain the place faux CAPTCHA pages are being leveraged to distribute malware, particularly Lumma Stealer. We’re observing a marketing campaign focusing on a number of nations. Beneath is a map displaying the geolocation of gadgets accessing faux CAPTCHA URLs, highlighting the worldwide distribution of the assault.

Determine 1: Prevalence on the sector

We recognized two an infection vectors main customers to those faux CAPTCHA pages: one through cracked sport obtain URLs, and the opposite by way of phishing emails. GitHub customers have been focused by phishing emails prompting them to deal with a fictitious “safety vulnerability” in a challenge repository to which they’ve contributed or subscribed. These emails direct customers to go to “github-scanner[.]com” for additional details about the alleged safety difficulty.

The ClickFix an infection chain operates by deceiving customers into clicking on buttons like “Confirm you’re a human” or “I’m not a robotic.” As soon as clicked, a malicious script is copied to the person’s clipboard. Customers are then misled into pasting the script after urgent the Home windows key + R, unknowingly executing the malware. This methodology of trickery facilitates the an infection course of, making it straightforward for attackers to deploy malware.

Determine 2: An infection chain

Assault Vectors and Technical Evaluation

As illustrated within the diagram, customers are redirected to faux CAPTCHA pages by way of two essential assault vectors:

1.     Cracked Gaming Software program Obtain URLs:

Customers trying to obtain pirated or cracked variations of gaming software program are redirected to malicious CAPTCHA pages.

Determine 3: Search to obtain the cracked model of the sport

When customers search the Web totally free or cracked variations of common video video games, they might encounter on-line boards, group posts, or public repositories that redirect them to malicious hyperlinks.

Determine 4: Runkit directing the person to obtain the sport

On this occasion, a public Runkit pocket book hosts the malicious hyperlink (highlighted in blue). When the person accesses the URL (highlighted in crimson), they’re redirected to faux CAPTCHA web sites.

Determine 5: Redirection taking place whereas accessing the hyperlink

On this web page, after the person clicks the “I’m not a robotic” button, a malicious PowerShell script is copied to their clipboard, and they’re prompted to execute it.

Determine 6: Backend script on the press button

The web site consists of JavaScript performance that copies the script to the clipboard.

Determine 7: Decoded script

The script is Base64-encoded (highlighted in blue), to scale back the readability to the person. Upon decoding it (highlighted in crimson), mshta was discovered to be leveraged. The file hosted at https://verif.dlvideosfre[.]click on/2ndhsoru accommodates a Home windows binary, having scripts appended because the overlay. With out the overlay appended, the file is a clear Home windows binary.

Determine 8: Home windows binary with appended script

The mshta utility searches for the <script> tag inside a file and executes the script embedded in it, utterly ignoring the binary portion of the file. This enables attackers to embed malicious scripts alongside non-executable content material, making it simpler for the malware to go undetected whereas nonetheless being executed by way of mshta.

Determine 9: Obfuscated script appended within the downloaded file

Upon evaluation, the script was discovered to be an encrypted JavaScript file, using two layers of encryption. This multi-level encryption obscures the script’s true performance, making detection and evaluation tougher for safety instruments. Additional evaluation revealed that the decrypted JavaScript was designed to obtain Lumma Stealer utilizing AES-encrypted PowerShell command and drop it within the Temp folder. This system helps the malware keep away from detection by putting the payload in a generally used, much less scrutinized listing, facilitating the following stage of the an infection.

Determine 10: Course of tree

2.     Phishing Emails impersonating the GitHub workforce

Within the second vector, customers obtain phishing emails, typically focusing on GitHub contributors, urging them to deal with a faux “safety vulnerability.” These emails comprise hyperlinks resulting in the identical faux CAPTCHA pages.

Determine 11: Phishing electronic mail impersonating GitHub

As soon as the person clicks on the hyperlink, they’re redirected to the faux captcha pages.

Determine 12: Faux CAPTCHA web page

These pages use the identical method: the malicious script is copied to the clipboard when the person clicks the button, and they’re then prompted to execute it.

Determine 13: Script copied onto clipboard

This script retrieves and executes the contents of a textual content file hosted on an internet server.

Determine 14: Invoking the distant script

The content material of the textual content file accommodates PowerShell instructions that obtain an executable file or a zipper file. These recordsdata are saved into the temp folder after which executed. The downloaded recordsdata, in these circumstances, are Lumma Stealer samples.

Detection and Mitigation Methods

McAfee blocks this an infection chain at a number of phases:

1. URL blocking of the faux CAPTCHA pages.

Determine 15: McAfee blocking URLs

2. Heuristic blocking of malicious use of mshta.

Determine 16: McAfee blocking the malicious habits

Conclusion and Suggestions

In conclusion, the ClickFix an infection chain demonstrates how cybercriminals exploit frequent person behaviors—equivalent to downloading cracked software program and responding to phishing emails—to distribute malware like Lumma Stealer. By leveraging faux CAPTCHA pages, attackers deceive customers into executing malicious scripts that bypass detection, in the end resulting in malware set up.

The an infection chain operates by way of two essential vectors: cracked gaming software program obtain URLs and phishing emails impersonating GitHub. In each circumstances, customers are redirected to malicious CAPTCHA pages the place scripts are executed to obtain and set up malware. Using multi-layered encryption additional complicates detection and evaluation, making these assaults extra subtle and more durable to forestall.

At McAfee Labs, we’re dedicated to serving to organizations defend themselves in opposition to subtle cyber threats, such because the Clickfix social engineering method. Listed here are our really helpful mitigations and remediations:

1. Conduct common coaching periods to coach customers about social engineering techniques and phishing schemes.
2. Set up and preserve up to date antivirus and anti-malware software program on all endpoints.
3. Implement sturdy electronic mail filtering to dam phishing emails and malicious attachments.
4. Use community segmentation to restrict the unfold of malware inside the group.
5. Guarantee all working programs, software program, and purposes are stored updated with the most recent safety patches.
6. Keep away from downloading cracked software program or visiting suspicious web sites.
7. Confirm URLs in emails, particularly from unknown or sudden sources.
8. Limit clipboard-based scripts and disable automated script execution.
9. Preserve antivirus options up to date and actively scan.
10. Educate customers to keep away from suspicious CAPTCHA prompts on untrusted websites.
11. Commonly patch browsers, working programs, and purposes.
12. Monitor the Temp folder for uncommon or suspicious recordsdata.

Indicators of Compromise (IoCs)

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