North Korean Hackers Deploys Backdoor Using Trojanized PuTTY SSH Client

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North Korean hackers are using a trojanized version of the PuTTY and KiTTY SSH utility to install backdoors on targets’ devices.

The attack begins with the threat actors sending phishing emails to victims offering them lucrative jobs on Amazon. Communication is taken to WhatsApp, where they share an ISO file called “amazon _assessment.iso”).

The ISO contains a text file “readme.txt” which contains an IP address and login data, as well as a trojanized version of PuTTY (PuTTY.exe), a popular open source SSH console application.

The discussion between the victim and the hackers remains unknown, but researchers believed they were told to open the ISO and use the included SSH tool and login credentials to connect to the host and conduct a competency assessment.

The PuTTY shared by the hackers was modified to include a malicious payload in its data area, making the manipulated version significantly larger than the legitimate version.

The modified PuTTY uses a malicious DAVESHELL shellcode payload in the form of a DLL. DAVESHELL is used as a dropper of the final payload, the AIRDRY.V2 backdoor malware.

Commands supported by AIRDRY.V2 include uploading basic system information, updating the beacon interval based on a value provided by the C2 server, disabling it until a new start date and time, uploading the current configuration, updating the beacon interval based on a value in the configuration, updating the AES key used to encrypt C2 requests and configuration data, and downloading and running a plugin in memory.

The sources for this piece include an article in BleepingComputer.


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