Ransomware Attackers Exploit VoIP Bug

The latest string of ransomware attacks has exploited a VoIP bug. More specifically, the bug in question is a Mitel VoIP bug. VoIP is an acronym commonly used to refer to Voice over Internet Protocol.

How is the Attack Performed?

The ransomware attackers are taking advantage of novel remote code execution exploits to obtain access to targets' environments. Additionally, unpatched Mitel VoIP versions are being used as a means of placing malware. As initially reported by Crowdstrike, the vulnerability was made public in April.  

What is the Response to the Exploit?

It appears as though the zero-day vulnerability has been patched. However, only time will tell if the patch proves successful.

Why is the VoIP Flaw Important?

The flaw highlights the vulnerabilities inherent to using VoIP technology. Mitel's VOIP empowers people to make web calls rather than phone calls.

Which Mitel VoIP Products are Affected?

Crowdstrike's digital security team indicates the vulnerability impacts Mitel's MiVoice SA 400, SA 100, and Virtual SA appliances. MiVoice is a unified interface used to enhance the coherence of digital communication and the tools necessary for those interactions over the web.  

Mitel's products are primarily used by businesses that covet efficient, reliable, and affordable phone services. An unaddressed flaw will make it challenging for the company's clients to interact with their clients and other important parties, ultimately impeding the flow of business. More than 20,000 Mitel VoIP devices are used across the world. The vast majority of those devices are used by parties in the United States and the United Kingdom.

How did the Hacker Obtain Access to the Targets?

The hacker or hacking collective behind this attack employed a creative strategy, using a novel remote code execution exploit. The hacker used the novel remote code execution exploit with two GET requests. 
The initial request zeroes in on a PHP file parameter of "get URL" and one that forms from the compromised device.

Why Does the Attack Include Two Requests?

The initial request was used as the susceptible URL wasn't permitted to receive requests transmitted from outside IP addresses. The ensuing request performs command injection with an HTTP GET request to the infrastructure that the hackers control. The second request is also necessary to catalyze the stored command as positioned on the attacker's server.

Digital security specialists who have studied the attack are adamant that the hacker relies on flaws to generate SSL-enabled reverse shells through "OpenSSL client" and "mkfifo" commands to transmit messages from the network after it has been compromised. The command forms a particular file identified through the file parameter. The file can then be opened for either writing or reading. The creation of the reverse shell sets the stage for a web shell referred to as "pdf_import.php" and the ensuing information theft.

What Should Mitel Customers Do?

Threat modeling will help to pinpoint potentially harmful activity on the network. It will also help to bolster your computer and network defenses with the industry's latest digital shields. Some cyber security specialists also suggest separating perimeter devices and critical assets to restrict access control in the event that the perimeter devices are violated.