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DNS query for known malicious domain cort.as

SIGmediumconfidence 86/100generated 2026-10-18

DNS resolution of a domain tracked by skopnix as apt-c-36 infrastructure.

ATT&CK
T1071 mitre ↗
Linked actors
APT-C-36
False positives
Scoped to one indicator with skopnix confidence 86/100 from 2 independent sources; checked against RFC1918/reserved space, CDN / cloud / scanner ranges and top-site lists (MISP warninglists), GreyNoise when enriched, and skopnix's benign-infrastructure list. Re-validate against last_seen before blocking: infrastructure is re-assigned.

Sigma rule

skopnix-sigma-ioc-domain-cort-as-a01a836e.ymldownload .yml ↓
title: Skopnix - DNS query for known malicious domain cort.as
id: f0a6a6a2-f8e8-587a-a77a-d09873a5dfc0
status: experimental
description: DNS resolution of a domain tracked by skopnix as apt-c-36 infrastructure.
references:
  - https://skopnix.com/ioc/cort.as
author: skopnix
date: '2026-10-18'
tags:
  - attack.command-and-control
  - attack.t1071
logsource:
  category: dns
detection:
  selection:
    query: cort.as
  condition: selection
falsepositives:
  - Legitimate services sharing the address; verify against skopnix confidence + last_seen
level: medium

How to deploy on Sigma

  1. 1.Convert for your SIEM with sigma-cli / pySigma, e.g. sigma convert -t splunk -p sysmon rule.yml.
  2. 2.Run it as a hunt first: every rule ships as status experimental.
  3. 3.Promote to an alert once a week of results is clean on your data.

Check · The processing pipeline must map the logsource (firewall, dns, proxy, webserver, process_creation) to your field names.

References