1200KM / sigma-rule
HTTP Request With Empty User Agent — Sigma Rule
Sigma rule 21e44d78-95e7-421b-a464-ffd8395659c4. HTTP Request With Empty User Agent — Sigma Rule. Detects a potentially suspicious empty user agent strings in proxy log. Could potentially indicate an uncommon request method.
Rule metadata and linked tags
Author: Florian Roth (Nextron Systems). Source status: test; severity: medium. Source dates: 2017-07-08 / 2021-11-27.
{
"category": "proxy"
}Pinned original Sigma rule · Detection Rule License 1.1
Source SHA-256: ea65359c4a8b22fe8154f8f7a22e5b71eaaa06bd47ce4fa1f35e1834db81f6f9
Detection logic
Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.
title: HTTP Request With Empty User Agent
id: 21e44d78-95e7-421b-a464-ffd8395659c4
status: test
description: |
Detects a potentially suspicious empty user agent strings in proxy log.
Could potentially indicate an uncommon request method.
references:
- https://twitter.com/Carlos_Perez/status/883455096645931008
author: Florian Roth (Nextron Systems)
date: 2017-07-08
modified: 2021-11-27
tags:
- attack.command-and-control
- attack.t1071.001
logsource:
category: proxy
detection:
selection:
# Empty string - as used by Powershell's (New-Object Net.WebClient).DownloadString
c-useragent: ''
condition: selection
falsepositives:
- Unknown
level: medium
False positives
- Unknown
Source references
Connected ecosystem references
Exact source-tagged techniques
Telemetry review
Read the original logsource above, then inspect the linked detection workspaces for technique-level sensor context. No per-rule telemetry equivalence is inferred.
Pinned research references. No browser attack runner, live simulation result or validated detector is asserted. Source mappings and validation limits are preserved. ATT&CK / Atomic provenance · Detection provenance.