BPFDoor — an active Chinese global surveillance tool

Recently, PwC Threat Intelligence documented the existence of BPFDoor, a passive network implant for Linux they attribute to Red Menshen, a Chinese threat actor group.

You can read more in PwC’s great, yearly threat intelligence brief, here.

PwC plan to present their findings in June:

BPFDoor is interesting. It allows a threat actor to backdoor a system for remote code execution, without opening any new network ports or firewall rules. For example, if a webapp exists on port 443, it can listen and react on the existing port 443, and the implant can be reached over the webapp port (even with the webapp running). This is because it uses a BPF packet filter.

Operators have access to a tool which allows communication to the implants, using a password, which allows features such as remotely executing commands. This works over internal and internet networks.

Because BPFDoor doesn’t open any inbound network ports, doesn’t use an outbound C2, and it renames its own process in Linux (so ps aux, for example, will show a friendly name) it is highly evasive.

I swept the internet for BPFDoor throughout 2021, and discovered it is installed at organisations in across the globe— in particular the US, South Korea, Hong Kong, Turkey, India, Viet Nam and Myanmar, and is highly evasive. These organisations include government systems, postal and logistic systems, education systems and more.

Inside those organisations I believe it is likely present on thousands of systems. The implant appears to be for surveillance purposes.

Per PwC:

We also identified that the threat actor sends commands to BPFDoor victims via Virtual Private Servers (VPSs) hosted at a well-known provider, and that these VPSs, in turn, are administered via…