Sigma rule: Katz Stealer Suspicious User-Agent

A detection rule from the SigmaHQ repository, shown as its author published it. Dataset version ref-3b7814bc63e2, updated 2025-05-22T00:00:00.000Z.

Rule

Title
Katz Stealer Suspicious User-Agent
Status
experimental
Level
high
Author
Swachchhanda Shrawan Poudel (Nextron Systems)
Date
2025-05-22
File
rules-emerging-threats/2025/Malware/Katz-Stealer/zeek_http_katz_stealer_susp_useragent.yml
Commit
ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects network connections with a suspicious user-agent string containing "katz-ontop", which may indicate Katz Stealer activity.

Log source

product
zeek
service
http

Detection

selection:
    user_agent|contains: 'katz-ontop'
condition: selection

False positives (as the rule lists them)

  • Unlikely

Tags

  • attack.command-and-control
  • attack.t1071.001
  • detection.emerging-threats

MITRE ATT&CK ids this rule names

References

  • Internal Research

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-emerging-threats/2025/Malware/Katz-Stealer/zeek_http_katz_stealer_susp_useragent.yml

Sources and licences

  • SigmaHQ

    "Katz Stealer Suspicious User-Agent" by Swachchhanda Shrawan Poudel (Nextron Systems) (SigmaHQ). Rule: https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-emerging-threats/2025/Malware/Katz-Stealer/zeek_http_katz_stealer_susp_useragent.yml.
    Licensed under the Detection Rule License (DRL) 1.1: https://github.com/SigmaHQ/Detection-Rule-License

    Detection Rule License (DRL) 1.1

Cite this page

Dragons Eye Ransomware Tracker, "Sigma rule: Katz Stealer Suspicious User-Agent",
entity page, dataset version ref-3b7814bc63e2, updated 2025-05-22T00:00:00.000Z,
https://ransomware-tracker.com/detections/sigma/834c6d2f-5e98-4b2a-b453-0c4f234afedd (accessed 2026-11-03).
Underlying source: SigmaHQ rule 834c6d2f-5e98-4b2a-b453-0c4f234afedd, commit ccbb0369507f796db0b0ae6854c8a2be471b9d84.

Pages change. The dataset version identifies the data, but no archive of old versions is kept, so this citation cannot be replayed later.