huntrule

Detect SolarWinds SUPERNOVA Webshell URL Access on Webservers (logoimagehandler.ashx)

Identifies webserver traffic consistent with SUPERNOVA webshell access targeting logoimagehandler.ashx with a clazz query parameter.

FreeReviewedSigma · Critical · v5
Category
webserver
Author
Florian Roth (Nextron Systems) (SigmaHQ), DRL 1.1
Published
2020-12-17
Updated
2026-07-31
AnalysisDetection
title: Detect SolarWinds SUPERNOVA Webshell URL Access on Webservers (logoimagehandler.ashx)
id: 29a42654-427f-4daf-b835-f2fdab0080b9
status: test
description: This rule flags web requests whose URL query parameters reference the SUPERNOVA webshell pattern for "logoimagehandler.ashx" and include "clazz". Attackers may use this functionality to establish persistence or execute malicious activity through a webshell, making targeted URL access a high-value signal. It relies on webserver HTTP request telemetry, specifically the requested URI query string and, in one case, a 500 response status.
references:
  - https://www.guidepointsecurity.com/supernova-solarwinds-net-webshell-analysis/
  - https://www.anquanke.com/post/id/226029
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2020/TA/SolarWinds-Supply-Chain/web_solarwinds_supernova_webshell.yml
author: Florian Roth (Nextron Systems), Huntrule Team
date: 2020-12-17
modified: 2023-01-02
tags:
  - attack.persistence
  - attack.t1505.003
  - detection.emerging-threats
logsource:
  category: webserver
detection:
  selection1:
    cs-uri-query|contains|all:
      - logoimagehandler.ashx
      - clazz
  selection2:
    cs-uri-query|contains: logoimagehandler.ashx
    sc-status: 500
  condition: selection1 or selection2
falsepositives:
  - Unknown
level: critical
license: DRL-1.1
related:
  - id: a2cee20b-eacc-459f-861d-c02e5d12f1db
    type: derived