Executive Summary
BPFDoor is a stealthy surveillance tool used by the threat actor group known as Red Menshen. It has recently evolved.
Key Takeaways
- BPFDoor is a stealthy surveillance tool used by the threat actor group known as Red Menshen.
- BPFDoor targets multiple Linux-based systems.
- BPFDoor has been in the wild for at least five years, is highly evasive, and is not detected by most endpoint protection vendors.
- BPFDoor has evolved this year, with some of the recent variants using more instructions than previous variants.
What is BPFDoor?
Trend Micro recently reported on the evolution of BPFDoor. BPFDoor is a stealthy surveillance tool used by the threat actor group known as Red Menshen. It targets multiple Linux-based systems, including Solaris SPARC. BPFDoor has been in the wild for at least five years, is highly evasive, and is not detected by most endpoint protection vendors.
Threat actors can use BPFDoor to backdoor a system for remote code execution with a single network packet and without opening new firewall rules or network ports. A web app existing on a particular port, such as port 443, can listen and react on the existing port, and the implant can be reached over the port. This is possible due to the use of a BPF packet filter.
BPFDoor loads classic BPF filters into a running kernel, expecting packets containing a magic number. When the correct packet arrives, BPFDoor connects to the source IP from which the matching packet was sent. BPFDoor opens a privileged reverse shell that the threat actor then uses to send commands to the victim machine’s shell via a pipe.
According to Trend Micro, BPFDoor variants from 2018 to 2022 use the same BPF program that accepts specific magic numbers for TCP, UDP, and ICMP protocols. Trend Micro divided the analysis of the different variants based on behavior. The pre-2023 sample, Variant A, leveraged a BPF program using 30 BPF instructions. The remaining samples were from 2023. Variant B used 39 instructions. Variant C used 205 instructions. Variant D used 229. Variant E was similar to a previous variant in that it used 30 instructions, but it used a different magic number.
Who is Red Menshen?
Red Menshen, also known as Red Dev 18, is a China nexus threat actor group active since at least 2021. Red Menshen’s targets include telecommunications entities in the Middle East and Asia. Other verticals the group targets include government, education, and logistics. Known TTPs include BPFDoor, Mangzamel, Mimikatz, Metasploit, and custom variants of Gh0st. Red Menshen also uses VPSs hosted at a well-known service provider and VPNs leveraging compromised routers located in Taiwan. The threat actors appear to be active on a regular schedule, operating Monday through Friday from the hours of 01:00 to 10:00 UTC.
IOCs
PolySwarm has multiple samples of BPFDoor.
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Cca78516c62e1b7cf3c56b665a3537dca6beb54d335c633454b325fd44c4f760
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A9884ba3ebf25dcb1b9b3319d5e9e3706832bfa0f1fc4248f22a065f7ef15f79
7906a1f358687ca1be8d9f531f066d6a5219857d37c13310c3239f10836007a8
28bfb3f2067c77b83898ef4e41c9fc573e6aaa8581da9b59bddb782205a0b091
B759020cbef57d96a5c978af3ae41bc1d9ffb7f3d521210a20b0d8d7540a13d4
Afa8a32ec29a31f152ba20a30eb483520fe50f2dce6c9aa9135d88f7c9c511d7
You can use the following CLI command to search for all BPFDoor samples in our portal:
$ polyswarm link list -f BPFDoor
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