Trojanized Version of PuTTY Distributed By Fake Amazon Job Phishers on WhatsApp

The makers of the secure telnet client PuTTY also sell a service monitoring company security services — and this July Mandiant Managed Defense "identified a novel spear phish methodology," according to a post on the company's blog:
[The threat cluster] established communication with the victim over WhatsApp and lured them to download a malicious ISO package regarding a fake job offering that led to the deployment of the AIRDRY.V2 backdoor through a trojanized instance of the PuTTY utility.... This activity was identified by our Mandiant Intelligence: Staging Directories mission, which searches for anomalous files written to directories commonly used by threat actors....

The amazon_assessment.iso archive held two files: an executable and a text file. The text file named Readme.txt had connection details for use with the second file: PuTTY.exe.... [T]he PuTTY.exe binary in the malicious archive does not have a digital signature. The size of the PuTTY binary downloaded by the victim is also substantially larger than the legitimate version. Upon closer inspection, it has a large, high entropy .data section in comparison to the officially distributed version. Sections like these are typically indicative of packed or encrypted data. The suspicious nature of the PuTTY.exe embedded in the ISO file prompted Managed Defense to perform a deeper investigation on the host and the file itself.

The execution of the malicious PuTTY binary resulted in the deployment of a backdoor to the host.

"The executable embedded in each ISO file is a fully functional PuTTY application compiled using publicly available PuTTY version 0.77 source code," the blog post points out.
Ars Technica notes that Mandiant's researchers believe it's being pushed by groups with ties to North Korea:

The executable file installed the latest version of Airdry, a backdoor the US government has attributed to the North Korean government. The US Cybersecurity and Infrastructure Security Agency has a description here. Japan's community emergency response team has this description of the backdoor, which is also tracked as BLINDINGCAN.

Read more of this story at Slashdot.