/
proxy_ua_susp.yml
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/
proxy_ua_susp.yml
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title: Suspicious User Agent
id: 7195a772-4b3f-43a4-a210-6a003d65caa1
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' # User-Agent: User-Agent:
- 'Mozilla/3.0 '
- 'Mozilla/2.0 '
- 'Mozilla/1.0 '
- 'Mozilla ' # missing slash
- ' Mozilla/' # leading space
- 'Mozila/' # single 'l'
- 'Mozilla/4.0 (compatible; MSIE 6.0; MS Web Services Client Protocol' # https://twitter.com/NtSetDefault/status/1303643299509567488
selection2:
c-useragent|contains:
- ' (compatible;MSIE ' # typical typo - missing space
- '.0;Windows NT ' # typical typo - missing space
- 'loader' # https://twitter.com/securityonion/status/1522614635152744453?s=20&t=gHyPTSq5A27EqKwrCd9ohg
selection3:
c-useragent:
- '_'
- 'CertUtil URL Agent' # https://twitter.com/stvemillertime/status/985150675527974912
- 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:60.0)' # CobaltStrike Beacon https://unit42.paloaltonetworks.com/tracking-oceanlotus-new-downloader-kerrdown/
- 'Mozilla/5.0 (Windows NT 6.3; WOW64; rv:28.0) Gecko/20100101 Firefox/28.0' # used by APT28 malware https://threatvector.cylance.com/en_us/home/inside-the-apt28-dll-backdoor-blitz.html
- 'HTTPS' # https://twitter.com/stvemillertime/status/1204437531632250880
- 'Erbium-UA-4ce7c27cb4be9d32e333bf032c88235a' # https://www.cyfirma.com/outofband/erbium-stealer-malware-report
- 'x' # Use by Racoon Stealer but could be something else
- 'xxx' # Use by Racoon Stealer but could be something else
falsepositives:
- c-useragent: 'Mozilla/3.0 * Acrobat *' # Acrobat with linked content
- cs-host|endswith: # Adobe product traffic, example: Mozilla/3.0 (compatible; Adobe Synchronizer 10.12.20000)
- '.acrobat.com'
- '.adobe.com'
- '.adobe.io'
condition: 1 of selection* and not falsepositives
falsepositives:
- Unknown
level: high