An advanced persistent threat known as Bitter has continued to target military organizations in Bangladesh with prolonged assaults.
In a recent report released on July 5, cybersecurity company SECUINFRA said that “threat actors undertake espionage by installing Remote Access Trojans through malicious document files and intermediary malware stages.”
The company’s research expands on a previous analysis from Cisco Talos published in May, which revealed the group’s expansion in targeting to hit Bangladeshi government entities using a backdoor known as ZxxZ. The company’s research has its headquarters in Berlin.
Bitter, also known by the codenames APT-C-08 and T-APT-17, has reportedly been active since at least late 2013 and has a history of deploying several tools, including BitterRAT and ArtraDownloader, to target Saudi Arabia, China, and Pakistan.
The most recent attack chain described by SECUINFRA is thought to have been carried out in mid-May 2022. It is thought to have started with a weaponized Excel document that was probably distributed via a spear-phishing email and, when opened, used the Microsoft Equation Editor exploit (CVE-2018-0798) to download the next-stage binary from a remote server.
The downloaded payload, ZxxZ (or MuuyDownloader by the Qi-Anxin Threat Intelligence Center), is implemented in Visual C++ and serves as a second-stage implant that enables the attacker to introduce further malware.
The most noticeable alteration in the malware is the substitution of an underscore for the “ZxxZ” separator used when transmitting data back to the command-and-control (C2) server, indicating that the organisation is actively making changes to its source code to avoid detection.
A backdoor known as Almond RAT, a.NET-based RAT that first surfaced in May 2022 and provides rudimentary data collecting capability and the ability to execute arbitrary instructions, is being utilised by the threat actor in its efforts. The infection also uses string encryption and obfuscation methods to avoid discovery and thwart analysis.
The researchers claimed that the major goals of almond RATs appeared to be file system detection, data exfiltration, and a mechanism to load other tools and create persistence. “The layout of the tools’ design seems to allow for rapid modification and adaptation to the present assault scenario.”