VPNFilter malware now targets new devices, even behind a firewall

The VPNFilter botnet now targeting new devices from other vendors, including ASUS, D-Link, Huawei, Ubiquiti, UPVEL, and ZTE.

The VPNFilter botnet is worse than initially thought, according to a new report published by Cisco Talos Intelligence group, the malicious code is now targeting ASUS, D-Link, Huawei, Ubiquiti, UPVEL, and ZTE

“First, we have determined that additional devices are being targeted by this actor, including some from vendors that are new to the target list. These new vendors are ASUS, D-Link, Huawei, Ubiquiti, UPVEL, and ZTE.” reads a new analysis published by Talos team.

“New devices were also discovered from Linksys, MikroTik, Netgear, and TP-Link. Our research currently shows that no Cisco network devices are affected.”

VPNFilter bot is now able to target endpoints behind the firewall and other network devices using a new stage 3 module that injects malicious content into web traffic

The recently discovered module dubbed “ssler” could be exploited by attackers to deliver exploits to endpoints via a man-in-the-middle capability (e.g. they can intercept network traffic and inject malicious code into it without the user’s knowledge).

“The ssler module, which we pronounce as “Esler,” provides data exfiltration and JavaScript injection capabilities by intercepting all traffic passing through the device destined for port 80. This module is expected to be executed with a parameter list, which determines the module’s behavior and which websites should be targeted.” continues the analysis.

VPNFilter initially infected over 500,000 routers and NAS devices, most of them in Ukraine, but fortunately, a prompt action of authorities allowed to take down it.

A week ago, experts from security firms GreyNoise Intelligence and JASK announced that the threat actor behind the VPNFilter is now attempting to resume the botnet with a new wave of infections.

Talos researchers confirmed that more devices from Linksys, MikroTik, Netgear, and TP-Link are affected, this means that the botnet could rapidly grow to infect new consumer or SOHO devices.

Talos already notified the attacks to the vendors, most of them promptly started working on new firmware to address the issue.

According to experts at Juniper Networks, the VPNFilter bot doesn’t exploit a zero-day vulnerability.

“The initial list of targeted routers included MicroTik, Linksys, NetGear, and TPLink. It is now expanded to include devices from ASUS, D-Link, Huawei, Ubiquiti, UPVEL and ZTE.” reads a post published by Juniper Network.

“We still do not believe this list is complete as more infected devices are being discovered. There is still no sign of any zero day vulnerability being exploited, so it is likely that known vulnerabilities and weak passwords are the main vector of infection.” 

The new attacks observed by Talos leverage compromised SOHO routers to inject content into web traffic using the ssler module.

The experts noticed that one of the parameters provided to the module it the source IP, a circumstance that suggests attackers might be profiling endpoints to pick out the best targets. The module is also able to monitor destination IP, likely to choose profitable targets, such as connection to a bank, or connections on which are credentials and other sensitive data are in transit.

The experts also provided further details on the device destruction module ‘dstr’ that attackers could use to render an infected device inoperable.

The dstr module is able to delete files necessary for normal operation of the infected device, it also deletes all files and folders related to its own operation to hide its presence to a forensic analysis.

“The dstr module clears flash memory by overwriting the bytes of all available /dev/mtdX devices with a 0xFF byte. Finally, the shell command rm -rf /* is executed to delete the remainder of the file system and the device is rebooted. At this point, the device will not have any of the files it needs to operate and fail to boot.” continues the analysis.

The following table published by El Reg shows all devices targeted by the VPNFilter bot, new ones are marked with an asterisk.

Further technical details are available in the report published by Talos.

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Pierluigi Paganini

(Security Affairs – VPNFilter botnet, malware)

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