Suspicious DNS Query with B64 Encoded String

SIGMA detection rule by Florian Roth (Nextron Systems) · NOASSERTION

Detects suspicious DNS queries using base64 encoding

title: Suspicious DNS Query with B64 Encoded String
id: 4153a907-2451-4e4f-a578-c52bb6881432
status: test
description: Detects suspicious DNS queries using base64 encoding
references:
    - https://github.com/krmaxwell/dns-exfiltration
author: Florian Roth (Nextron Systems)
date: 2018-05-10
modified: 2022-10-09
tags:
    - attack.exfiltration
    - attack.t1048.003
    - attack.command-and-control
    - attack.t1071.004
logsource:
    category: dns
detection:
    selection:
        query|contains: '==.'
    condition: selection
falsepositives:
    - Unknown
level: medium

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

ff951b16-b6d3-4120-acbd-dd7836425333

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

[[ reason ]]

What does this mean?

Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

[[ reason ]]

What do these messages mean?

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

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