LightBasin is a sophisticated threat actor that has established a persistent, long term presence in the heart of the network of at least 13 telecommunication companies around the world since 2019.

According to research from Crowdstrike, the threat actor group known as UNC1945 or LightBasin, has been infiltrating the Linux and Solaris systems which run the core telco networks.  The investigation has uncovered the tactics, techniques and procedures employed by the attackers which are a combination of the sophisticated and the disappointingly simple.

Weak Passwords

It is thought initial access to the network was obtained via the DNS servers which are part of the GPRS (General Packet Radio Service) network.  The attackers used password spraying using very weak and third party related passwords (such as vendor and supplier company names) as part of the initial compromise.  Once a foothold was established on the DNS server, communication was possible between different DNS servers compromised by the attackers in different telcos all connected to GPRS using shell traffic sent over TCP port 53 to disguise it as DNS traffic.

Replacing System Utilities

In order to facilitate their movement within a telco and across the GPRS network into other telcos, the attackers added rules to the firewall on the compromised servers.  In order to hide these changes, the attackers then replaces the iptables binary which is used to configure the Netfilter firewall. The updated iptables altered its output to omit the rules added by the hackers – thus any admin who thought to check the firewall rules would not observe anything out of place

Lax monitoring

Crowdstrike observed that in many of the telco networks, basic security controls were not implemented for core systems in the heart of the network. For example, SSH traffic was not logged nor were syslogs forwarded to SIEM systems for centralised review and monitoring. File integrity monitoring was not in place, allowing system utilities to be replaced with malicious versions.

The full report provides detailed Indicators of Compromise and further explanation of some of the sophisticated techniques employed by the LightBasin group.   There is no clear evidence yet where the group is based, but the level of sophistication and the scale of the attack makes it clear it is the work of a nation state’s security service.