A recently discovered Remote Access Trojan (RAT) is being distributed via documents that exploit a 17-year old Office vulnerability patched in November 2017, Netskope warns.

Dubbed TelegramRAT, the malware leverages the Telegram Messenger application for command and control (C&C), and abuses a cloud storage platform to store its payload. This approach allows the threat to evade some traditional security scanners.

Attacks involving TelegramRAT start with a malicious Office document exploiting CVE-2017-11882, a vulnerability that was introduced in the Microsoft Equation Editor (EQNEDT32.EXE) in November 2000. The bug remained unnoticed for 17 years, until Microsoft manually patched it last month, but it didn’t take long for malicious actors to start abusing it.

As part of the newly observed attack, the Bit.ly URL redirection service is used to conceal the TelegramRAT payload hosted on Dropbox. The malware uses the Telegram BOT API to receive commands and send responses to the attacker. By employing SSL cloud applications for infection and C&C operations, the malware can keep communication hidden from security applications.

“The payload executable strings contained lots of references to Python files. After a quick analysis, the payload looked to be a Python program converted into a standalone binary executable that contained everything needed to run the application,” Netskope says.

Because the Python interpreter, the application code, and all the required libraries are packaged, the executable is large in size, which also makes it less suspicious.

Within the extracted directory, the researchers found PYD files, DLL files, and an out00-PYZ.pyz_extracted folder containing .pyc files. They also discovered a file called “RATAttack” which points to an open-source “RAT-via-Telegram” on GitHub.

The attackers used almost the exact code from GitHub when compiling their Python executable, the security researchers have discovered.

By using Telegram, which supports encrypted communication, the attackers ensure that they can easily communicate with the target without anyone snooping into the communication. The RAT’s authors create a Telegram bot and embed the bot’s Telegram token into the TelegramRAT’s configuration file. The malware then connects to the bot’s Telegram channel, where the attacker can issue commands for the infected machines.

Based on the received commands, the malware can take screenshots, execute shell commands, copy files, delete files/folders, download file from target, encode local files and decode them, enable/disable keyboard freeze, get Google Chrome’s login/passwords, record microphone, get keylogs, get PC information, open a proxy server, reboot/shut down the machine, run a file, schedule a command to run at specific time, display services and processes running, and update executable.

“TelegramRAT offers another unfortunate instance of attackers recognizing that the cloud can be leveraged to evade many traditional security scanners. By making itself cloud native, TelegramRAT uses one cloud application for its payload host, and another for its C&C operation. This cloud application splicing offers resilience to the attack, and requires security scanners to be able to discern cloud application instances, and to inspect SSL traffic to be effective,” Netskope concludes.

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