Potential Base64 Encoded User-Agent

Description

Detects User Agent strings that end with an equal sign, which can be a sign of base64 encoding.

Query · sigma

selection:
  c-useragent|endswith: '='
condition: selection

Known false positives

  • Unknown
Raw source Potential Base64 Encoded User-Agent · Sigma
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Published by SigmaHQ/sigma ↗, licensed under Detection Rule License 1.1 ↗. Reproduced here unmodified. 
title: Potential Base64 Encoded User-Agent
id: 894a8613-cf12-48b3-8e57-9085f54aa0c3
related:
    - id: d443095b-a221-4957-a2c4-cd1756c9b747
      type: derived
status: test
description: Detects User Agent strings that end with an equal sign, which can be a sign of base64 encoding.
references:
    - https://blogs.jpcert.or.jp/en/2022/07/yamabot.html
    - https://deviceatlas.com/blog/list-of-user-agent-strings#desktop
author: Florian Roth (Nextron Systems), Brian Ingram (update)
date: 2022-07-08
modified: 2023-05-04
tags:
    - attack.command-and-control
    - attack.t1071.001
logsource:
    category: proxy
detection:
    selection:
        c-useragent|endswith: '='
    condition: selection
falsepositives:
    - Unknown
level: medium

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