name: Linux Proxy Socks Curl
id: bd596c22-ad1e-44fc-b242-817253ce8b08
version: 1
date: '2022-07-29'
author: Michael Haag, Splunk
status: production
type: TTP
description: The following analytic identifies curl being utilized with a proxy based
  on command-line arguments - -x, socks, --preproxy and --proxy. This behavior is
  built into the MetaSploit Framework as a auxiliary module. What does socks buy an
  adversary? SOCKS4a extends the SOCKS4 protocol to allow a client to specify a destination
  domain name rather than an IP address. The SOCKS5 protocol is defined in RFC 1928.
  It is an incompatible extension of the SOCKS4 protocol; it offers more choices for
  authentication and adds support for IPv6 and UDP, the latter of which can be used
  for DNS lookups. The protocols, and a proxy itself, allow an adversary to evade
  controls in place monitoring traffic, making it harder for the defender to identify
  and track activity.
data_source:
- Sysmon Event ID 1
search:
  selection1:
    CommandLine:
    - '*-x *'
    - '*socks4a://*'
    - '*socks5h://*'
    - '*socks4://*'
    - '*socks5://*'
    - '*--preproxy *'
    - --proxy*
    Image|endswith: curl
  condition: selection1
how_to_implement: To successfully implement this search you need to be ingesting information
  on process that include the name of the process responsible for the changes from
  your endpoints into the `Endpoint` datamodel in the `Processes` node. In addition,
  confirm the latest CIM App 4.20 or higher is installed and the latest TA for the
  endpoint product.
known_false_positives: False positives may be present based on proxy usage internally.
  Filter as needed.
references:
- https://www.offensive-security.com/metasploit-unleashed/proxytunnels/
- https://curl.se/docs/manpage.html
- https://en.wikipedia.org/wiki/SOCKS
- https://oxylabs.io/blog/curl-with-proxy
- https://reqbin.com/req/c-ddxflki5/curl-proxy-server#:~:text=To%20use%20a%20proxy%20with,be%20URL%20decoded%20by%20Curl.
- https://gtfobins.github.io/gtfobins/curl/
tags:
  analytic_story:
  - Linux Living Off The Land
  - Ingress Tool Transfer
  asset_type: Endpoint
  confidence: 80
  impact: 70
  message: An instance of $process_name$ was identified on endpoint $dest$ by user
    $user$ utilizing a proxy. Review activity for further details.
  mitre_attack_id:
  - T1090
  - T1095
  observable:
  - name: user
    type: User
    role:
    - Victim
  - name: dest
    type: Hostname
    role:
    - Victim
  - name: process_name
    type: Process
    role:
    - Child Process
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  risk_score: 56
  security_domain: endpoint
tests:
- name: True Positive Test
  attack_data:
  - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1105/atomic_red_team/curl-linux-sysmon.log
    source: Syslog:Linux-Sysmon/Operational
    sourcetype: sysmon_linux
    update_timestamp: true