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Bpfdoor TCP Ports Redirect

All TCP traffic on particular port from attacker is routed to different port. ex. '/sbin/iptables -t nat -D PREROUTING -p tcp -s 192.168.1.1 --dport 22 -j REDIRECT --to-ports 42392' The traffic looks like encrypted SSH communications going to TCP port 22, but in reality is being directed to the shell port once it hits the iptables rule for the attacker host only.

MITRE ATT&CK

T1562.004

defense-evasion

Detection Query

cmd:
  type: EXECVE
  a0|endswith: iptables
  a1: -t
  a2: nat
keywords:
  - --to-ports 42
  - --to-ports 43
condition: cmd and keywords

Author

Rafal Piasecki

Created

2022-08-10

Data Sources

linuxauditd

Platforms

linux

References

Tags

attack.defense-evasionattack.t1562.004

Raw Content

title: Bpfdoor TCP Ports Redirect
id: 70b4156e-50fc-4523-aa50-c9dddf1993fc
status: test
description: |
    All TCP traffic on particular port from attacker is routed to different port. ex. '/sbin/iptables -t nat -D PREROUTING -p tcp -s 192.168.1.1 --dport 22 -j REDIRECT --to-ports 42392'
    The traffic looks like encrypted SSH communications going to TCP port 22, but in reality is being directed to the shell port once it hits the iptables rule for the attacker host only.
references:
    - https://www.sandflysecurity.com/blog/bpfdoor-an-evasive-linux-backdoor-technical-analysis/
    - https://www.elastic.co/security-labs/a-peek-behind-the-bpfdoor
author: Rafal Piasecki
date: 2022-08-10
tags:
    - attack.defense-evasion
    - attack.t1562.004
logsource:
    product: linux
    service: auditd
detection:
    cmd:
        type: 'EXECVE'
        a0|endswith: 'iptables'
        a1: '-t'
        a2: 'nat'
    keywords:
        - '--to-ports 42'
        - '--to-ports 43'
    condition: cmd and keywords
falsepositives:
    - Legitimate ports redirect
level: medium