Ursnif Malware C2 URL Pattern

SIGMA detection rule by Thomas Patzke · NOASSERTION

Detects Ursnif C2 traffic.

title: Ursnif Malware C2 URL Pattern
id: 932ac737-33ca-4afd-9869-0d48b391fcc9
status: stable
description: Detects Ursnif C2 traffic.
references:
    - https://www.fortinet.com/blog/threat-research/ursnif-variant-spreading-word-document.html
author: Thomas Patzke
date: 2019-12-19
modified: 2021-08-09
tags:
    - attack.initial-access
    - attack.t1566.001
    - attack.execution
    - attack.t1204.002
    - attack.command-and-control
    - attack.t1071.001
    - detection.emerging-threats
logsource:
    category: proxy
detection:
    b64encoding:
        c-uri|contains:
            - '_2f'
            - '_2b'
    urlpatterns:
        c-uri|contains|all:
            - '.avi'
            - '/images/'
    condition: b64encoding and urlpatterns
falsepositives:
    - Unknown
level: critical

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

62302056-8928-4866-886d-dc6056f2fc3e

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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

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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.

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

[[ currentRule.title ]]

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