Ryuk ransomware now self-spreads to other Windows LAN devices


Ryuk ransomware now self-spreads to other Windows LAN devices

A new Ryuk ransomware variant with worm-like capabilities that allow it to spread to other devices on victims’ local networks has been discovered by the French national cyber-security agency while investigating an attack in early 2021.

“Through the use of scheduled tasks, the malware propagates itself – machine to machine – within the Windows domain,” ANSSI (short for Agence Nationale de la Sécurité des Systèmes d’Information) said in a report published today.

“Once launched, it will thus spread itself on every reachable machine on which Windows RPC accesses are possible.”

Self-replication to other network devices

To propagate itself over the local network, the new Ryuk variant lists all the IP addresses in the local ARP cache and sends what looks like Wake-on-LAN (WOL) packets to each of the discovered devices. It then mounts all sharing resources found for each device so that it can encrypt the contents.

Ryuk’s ability to mount and encrypt remote computers’ drives was previously observed by Advanced Intelligence CEO Vitali Kremez last year.

What makes this new Ryuk sample different is its capability to copy itself to other Windows devices on the victims’ local networks.

Additionally, it can execute itself remotely using scheduled tasks created on each subsequently compromised network host with the help of the legitimate schtasks.exe Windows tool.

The Ryuk variant analyzed in this document does have self-replication capabilities. The propagation is achieved by copying the executable on identified network shares. This step is followed by the creation of a scheduled task on the remote machine. [..] Some filenames were identified for this copy: rep.exe and lan.exe. – ANSSI

Example scheduled task
Example scheduled task (BleepingComputer)

While it doesn’t use an exclusion mechanism that would prevent it from re-encrypting devices, ANSSI says that the new variant can still be blocked from infecting other hosts on the network by changing the password of the privileged domain account it uses for propagation to other hosts.

“One way to tackle the problem could be to change the password or disable the user account (according to the used account) and then proceed to a double KRBTGT domain password…

Source…