AutoIt scripting increasingly used by malware developers

Flexibility and ease of use fuels surge in malware samples created with the AutoIt scripting language, security researchers say

AutoIt, a scripting language for automating Windows interface interactions, is increasingly being used by malware developers thanks to its flexibility and low learning curve, according to security researchers from Trend Micro and Bitdefender.

"Recently, we have seen an uptick in the amount of nefarious AutoIt tool code being uploaded to Pastebin," Kyle Wilhoit, a threat researcher at antivirus vendor Trend Micro, said Monday in a blog post. "One commonly seen tool, for instance, is a keylogger. Grabbing this code, anyone with bad intentions can quickly compile and run it in a matter of seconds."

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"In addition to tools being found on sites like Pastebin and Pastie, we are also seeing a tremendous increase in the amount of malware utilizing AutoIt as a scripting language," Wilhoit said.

The use of AutoIt in malware development has steadily increased since 2008, Bogdan Botezatu, a senior e-threat analyst at antivirus vendor Bitdefender said Tuesday via email. The number of malware samples coded in AutoIt has recently peaked at more than 20,000 per month, he said.

"In its early days, AutoIt malware was mostly used for advertising fraud or to create self-propagation mechanisms for IM [instant messaging] worms," Botezatu said. "Nowadays, AutoIt malware ranges from ransomware to remote access applications."

One particularly sophisticated piece of AutoIt-based malware discovered recently was a version of the DarkComet RAT (remote access Trojan program), Wilhoit said. This malware opens a backdoor on the victim's machine, communicates with a remote command and control server and modifies Windows firewall policies, he said.

The DarkComet RAT has been used in targeted, APT-style, attacks in the past, including by the Syrian government to spy on political activists in the country. What's interesting about the variant found by Trend Micro is that it's written in AutoIt and has a very low antivirus detection rate.

The use of scripting languages to develop sophisticated malware is not a widespread practice, because most of these languages require an interpreter to be installed on the machine or produce very large stand-alone executable files, Botezatu said.

However, there have been exceptions. For example, the Flame cyberespionage malware used the LUA scripting language to automate some tasks without being detected by antivirus products, Botezatu said.

AutoIt is extremely intuitive and easy to use, produces compiled binaries that run out of the box on modern Windows versions and is well documented, the Bitdefender researcher said. Also, there is already a lot of malicious AutoIt code available on the Web for reuse, he said.

"Most importantly, malware created in AutoIt is extremely flexible and can be easily obfuscated, which means that a single breed of malware written in AutoIt can be repackaged and re-crafted in a number of ways to prevent detection and extend its shelf life," Botezatu said.

As scripting languages like AutoIt continue to gain popularity, more malware developers are expected to migrate toward them, Wilhoit said. "The ease of use and learning, as well as the ability to post code easily to popular dropsites make this a great opportunity for actors with nefarious intentions to propagate their tools and malware."

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