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Not so random: Reductor malware hijacks HTTPS traffic by manipulating browsers’ “random” numbers generator

October 2019 by Kaspersky Lab

Kaspersky researchers have discovered new malware that hijacks victims’ interaction with HTTPS web pages via patching the pseudo random number generator used in the process of establishing encrypted communication between the user and the website. Along with the installation of rogue digital certificates it gives the actors the ability to spy on users’ browser activity.

While the “S” in HTTPS stands for “Secure” and infers that information exchanged between a browser and a website is not accessible to third parties, there still are many ways for a skilled high-profile hacking group to interfere in this process. Reductor is a tool developed for such intrusion and was used for cyber-espionage on diplomatic entities in CIS countries, primarily by monitoring their employees’ internet traffic. What’s more, the found modules had RAT (Remote Administration Tool) functions and the capabilities of this malware were almost unlimited. Reductor distributors had two main attack vectors, one of which consisted of having modules downloaded through COMPfun malware, previously attributed to the Turla Russian-speaking threat actor. Another vector seemed to be trickier: apparently the attacker had the opportunity to patch clean software on the fly while it is being downloaded from legitimate websites to users’ computers. The software installers, downloaded from the warez websites which offer free downloads of pirated software. While the original installers available on those websites were not infected, they would end up on the victims’ PCs carrying malware. Kaspersky researchers concluded that replacement happens on the fly and that Reductor’s operators have some control over the target’s network channel.

Once Reductor found its way to the victim’s device, it would manipulate installed digital certificates, patching browsers’ pseudo random number generators used to encrypt the traffic coming from the user to HTTPS websites. To identify victims, whose traffic is hijacked, the criminals would add unique hardware- and software-based identifiers for each of them and mark them with certain numbers in a not-so-random-anymore numbers generator. Once the browser on the infected device is patched, the threat actor receives all information and actions performed with this browser, while the victim remains unsuspecting of anything untoward.

“We haven’t seen malware developers interacting with browser encryption in this way before” comments Kurt Baumgartner, security researcher at Kaspersky’s Global Research and Analysis Team. “It is elegant in a way and allowed attackers to stay well under the radar for a long time. The level of sophistication of the attack method suggests that the creators of Reductor malware are highly professional - which is quite common among nation-state backed actors. However we weren’t able to find solid technical clues which would attach this malware to any known threat actor. We urge all organisations dealing with sensitive data to stay alert and have regular, thorough security checks.”

Kaspersky products successfully detect and block Reductor malware.

To avoid being affected by malware, such as Reductor, Kaspersky recommends:
• Performing regular security audit of an organisation’s IT infrastructure
• Adopting proven security solutions equipped with web threat protection that identifies and blocks threats that attempt to use encrypted channels to penetrate the system undetectedlike Kaspersky Endpoint Security for Business
• In addition to adopting essential endpoint protection, implement a corporate-grade security solution that detects advanced threats on the network level at an early stage, such as Kaspersky Anti Targeted Attack Platform.
• Providing your SOC team with access to the latest Threat Intelligence, to keep up to date with the new and emerging tools, techniques and tactics used by threat actors and cybercriminals.
• Implementing security awareness training sessions for staff so that they will know the risk assotiated with pirated software and how to distinguish it.

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