Behind the CAPTCHA: A Intelligent Gateway of Malware

Authored by Yashvi Shah and Aayush Tyagi

Government abstract

McAfee Labs lately noticed an an infection chain the place pretend CAPTCHA pages are being leveraged to distribute malware, particularly Lumma Stealer. We’re observing a marketing campaign focusing on a number of international locations. Beneath is a map displaying the geolocation of units accessing pretend 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 pretend CAPTCHA pages: one by way of cracked sport obtain URLs, and the opposite by phishing emails. GitHub customers have been focused by phishing emails prompting them to handle a fictitious “safety vulnerability” in a venture 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 consumer’s clipboard. Customers are then misled into pasting the script after urgent the Home windows key + R, unknowingly executing the malware. This technique 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 pretend CAPTCHA pages by two predominant assault vectors:

1.     Cracked Gaming Software program Obtain URLs:

Customers making an attempt 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 without spending a dime or cracked variations of standard 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 consumer to obtain the sport

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

Determine 5: Redirection occurring whereas accessing the hyperlink

On this web page, after the consumer 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 consumer. Upon decoding it (highlighted in purple), mshta was discovered to be leveraged. The file hosted at https://verif.dlvideosfre[.]click on/2ndhsoru comprises 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, fully 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 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 method helps the malware keep away from detection by inserting 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, usually focusing on GitHub contributors, urging them to handle a pretend “safety vulnerability.” These emails include hyperlinks resulting in the identical pretend CAPTCHA pages.

Determine 11: Phishing e-mail impersonating GitHub

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

Determine 12: Pretend CAPTCHA web page

These pages use the identical approach: the malicious script is copied to the clipboard when the consumer 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 a web based server.

Determine 14: Invoking the distant script

The content material of the textual content file comprises 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 levels:

1. URL blocking of the pretend CAPTCHA pages.

Determine 15: McAfee blocking URLs

2. Heuristic blocking of malicious use of mshta.

Determine 16: McAfee blocking the malicious conduct

Conclusion and Suggestions

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

The an infection chain operates by two predominant 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. The usage of multi-layered encryption additional complicates detection and evaluation, making these assaults extra subtle and more durable to stop.

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

1. Conduct common coaching periods to teach customers about social engineering ways and phishing schemes.
2. Set up and keep up to date antivirus and anti-malware software program on all endpoints.
3. Implement strong e-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 techniques, software program, and purposes are saved 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. Prohibit clipboard-based scripts and disable computerized 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. Recurrently patch browsers, working techniques, and purposes.
12. Monitor the Temp folder for uncommon or suspicious recordsdata.

Indicators of Compromise (IoCs)

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