Suspicious User Agent

Title: Suspicious User Agent
Status: test
Description:Detects suspicious malformed user agent strings in proxy logs
References:
  -https://github.com/fastly/waf_testbed/blob/8bfc406551f3045e418cbaad7596cff8da331dfc/templates/default/scanners-user-agents.data.erb
Author: Florian Roth (Nextron Systems)
Date: 2017-07-08
modified:2022-10-31
Tags:

• -'attack.command-and-control'
• -'attack.t1071.001'

Logsource:

• category: proxy

Detection:
  selection1:
    c-useragent|startswith:
      -'user-agent'
      -'Mozilla/3.0 '
      -'Mozilla/2.0 '
      -'Mozilla/1.0 '
      -'Mozilla '
      -' Mozilla/'
      -'Mozila/'
      -'Mozilla/4.0 (compatible; MSIE 6.0; MS Web Services Client Protocol'

  selection2:
    c-useragent|contains:
      -' (compatible;MSIE '
      -'.0;Windows NT '
      -'loader'

  selection3:
    c-useragent:
      -'_'
      -'CertUtil URL Agent'
      -'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:60.0)'
      -'Mozilla/5.0 (Windows NT 6.3; WOW64; rv:28.0) Gecko/20100101 Firefox/28.0'
      -'HTTPS'
      -'Erbium-UA-4ce7c27cb4be9d32e333bf032c88235a'
      -'x'
      -'xxx'

  falsepositives:
c-useragent:'Mozilla/3.0 * Acrobat *'     - cs-host|endswith:
      - '.acrobat.com'
      - '.adobe.com'
      - '.adobe.io'
  condition:1 of selection* and not falsepositives
Falsepositives:
  -Unknown
Level: high