Dell SecureWorks Counter Threat Unit™ has released information about Stegoloader. Appearing to have been active since 2012, this particular malware uses digital steganography – the art of hiding secret information within a digital image or graphic – to conceal its true nature and to avoid detection.
Stegoloader operators are hiding a core component of the malware within a portable network graphic (PNG) hosted on a legitimate site. As Stegoloader executes, it downloads the core component and then uses digital steganography to extract the code from the image.
The core component is never saved to the victim’s computer, meaning that it is incredibly difficult to detect the malware through regular tools.
Various top security experts were keen to offer their thoughts on the topic:
Szilard Stange, director, OPSWAT:
“Malware authors are always looking for new distribution mechanism to make detection harder; however modern internet security desktop suites contain methods to detect unusual network operations even when the remote site is a well known site. They are also able to track what the running processes exactly do.
"It means that detection of malware like Stegoloader can be harder but not impossible. There are many ways to deliver harmful content including this steganography based one, but there are other interesting ways to distribute harmful code like embedded data into DNS queries/responses.
"Any of them can be in main-stream but it mainly depends how anti-malware vendors can react to these attacks. To protect an organisation against attacks like this one, it is worth to consider applying data sanitization techniques to remove any harmful content from images downloaded from the internet without losing important data.”
Martin Lee, intelligence manager, Alert Logic:
“We are currently in an arms race between malware writers and the security industry. As security researchers become more adept in discovering malware, so malware writers must become more inventive in hiding their malware.
"In many ways, seeing malware writers deploying inventive strategies to disguise and hide their malware is proof that security solutions are making it difficult for malware to persist and that we are forcing malware writers to innovate. Even if this malware is hiding itself on the end point, the command and control traffic is still visible on the network.
"Monitoring for traffic to known command and control servers or anomalous traffic remains an excellent technique for identifying the presence of malware, even if identifying and reverse engineering the malware becomes more difficult."
Gavin Reid, VP threat intelligence, Lancope:
“Stenography has never gone away – it is used less for malware propagation and more to obscure the command and control instructions sent from an infected hosts to the controller.
"A typical use case would be a check-in by infected host for new instructions over a web request. If this check-in was observed by the security team then would only see a web browser pulling down a graphic which is typical user activity happening all the time and would most likely avoid detection.
"Will Stegoloader become “mass-market” and be used by lots of criminals? Possibly in the future – however with the widespread success of less “stealthy” malware stenography is not necessarily needed. For example, we still have millions of conficker infections – a 6 year old easy to detect virus.
"Normal patching and security controls, host based IDS, along with robust incident detection and response to catch system that are impacted – in particular the ability to take in and operationalise new threat intelligence across your entire organisation."