Kirts

Overview

Kirts (classified across antimalware research as Ransom:Win32/Kirts and Trojan-Ransom.Win32.Kirts) is a targeted crypto-ransomware family designed to execute destructive file encryption across Windows endpoints and file servers. Propagated through weaponized email attachments and compromised RDP connections, Kirts terminates running office and database processes to clear file locks before encryption. It leverages AES-256 symmetric encryption to lock files and appends .kirts to filenames, placing ransom notes titled HOW_TO_RESTORE_KIRTS.txt in affected directories. To ensure payment compliance, Kirts executes shell commands to purge Volume Shadow Copies via vssadmin and disables Windows startup recovery.

Known aliases

Threat reports may refer to this family under multiple names:

• Ransom:Win32/Kirts
• Trojan-Ransom.Win32.Kirts
• Win32/Kirts
• Kirts Ransomware
• Ransom.Kirts

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.
• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

Tiered Detection Rules (Cisco CAIRN Model)

Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:

rule MALWARE_WIN_KIRTS_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Kirts"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "kirts" ascii wide nocase
        $s2 = "ransom:win32/kirts" ascii wide nocase
        $s3 = "trojan-ransom.win32.kirts" ascii wide nocase
        $s4 = "win32/kirts" ascii wide nocase
        $s5 = "kirts ransomware" ascii wide nocase
        $s6 = "ransom.kirts" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Kirts (Ransomware) Execution & Triage
id: 2e59ad58-0b78-5850-9a5d-d8ff7dd8b117
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Kirts malware family. Detects volume shadow copy deletion, boot status
  tampering, and recovery inhibition characteristic of modern ransomware operations.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/kirts
- https://malware-families-catalog.systemhelpdesk.com/defensive/ransomware-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.ransomware
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1486
- attack.t1562_001
- attack.t1490
- attack.t1083
- attack.t1135
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \vssadmin.exe
    - \wmic.exe
    - \wbadmin.exe
    - \bcdedit.exe
    CommandLine|contains:
    - delete shadows
    - shadowcopy delete
    - resize shadowstorage
    - recoveryenabled no
    - ignoreallfailures
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: critical

rule MALWARE_WIN_KIRTS_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Kirts tradecraft"
        tier = "T3 - Attribution Fingerprint"
        confidence = "High (Confirmed Family Signature)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        // Core family identifier & heuristic payload signatures
        $attrib_str = "kirts" ascii wide nocase
        $pe_magic = "MZ" ascii
        $net_marker = "http" ascii nocase
    condition:
        uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

1. Isolate the endpoint immediately to prevent Kirts from downloading and executing its secondary payloads (e.g., ransomware).
2. Audit the Windows Task Scheduler and Registry Run keys to identify and remove the Kirts persistence mechanisms.
3. Review firewall and proxy logs to identify the C2 domains Kirts attempted to contact, and block them enterprise-wide.
4. Capture a live memory image (RAM dump) to extract the injected Kirts modules and identify the secondary payloads.

What to Avoid

Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.

1. Do not close an incident simply because the initial Kirts dropper was quarantined; always verify if secondary payloads were downloaded.
2. Avoid relying solely on manual file deletion, as the injected processes will likely just recreate the dropped binaries.

References & External Analysis

• Microsoft Defender Threat Encyclopedia - Ransom:Win32/Kirts
• Kaspersky Threat Intelligence - Trojan-Ransom Overview
• MITRE ATT&CK - Data Encrypted for Impact (T1486)
• Search "kirts" on VirusTotal (External Analysis)
• Search "kirts" on Any.Run (Sandbox Sandbox)
• Search "kirts" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Ransomware)

Explore other documented threats in the same operational category:

• Babonock
• Eziriznetreactor
• Kraddare
• Xxycdl
• Tufik
• Enistery
• Wemosis
• Selcry

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/kirts.json

Ecosystem & Interactive Environments

This profile is part of the Malware Families Catalog, a public dataset of 2,899 malware families. The catalog is also published across our ecosystem: Hugging Face, Kaggle, Zenodo, Replit, StackBlitz, CodeSandbox, and CodePen.