Sigrun

Overview

Ransom:Win32/Sigrun is a highly destructive Cryptographic Ransomware family designed to extort money from victims by rendering their data inaccessible. Like most modern ransomware, it relies on strong cryptographic algorithms to lock files, demanding payment in cryptocurrency in exchange for the decryption key.

Understanding Sigrun (Ransomware)
To an end-user, the impact is devastating: critical documents, databases, and media files are encrypted and appended with a specific extension, followed by the display of a ransom note on the desktop. For a security operations center (SOC), a Sigrun infection represents a critical incident requiring immediate containment to prevent the infection from spreading to network shares and crippling organizational infrastructure.

Execution and Encryption Mechanics
Sigrun is typically delivered via phishing emails containing malicious attachments (`T1566.001`), drive-by downloads, or by exploiting exposed Remote Desktop Protocol (RDP) services (`T1133`). Upon execution (`T1204.002`), it establishes persistence, often via the Registry Run keys or Scheduled Tasks (`T1547.001`). Crucially, before encrypting files, Sigrun executes commands (like `vssadmin.exe delete shadows` or `bcdedit /set {default} recoveryenabled No`) to inhibit system recovery (`T1490`). It then iterates through local drives and accessible network shares, utilizing strong encryption (e.g., AES + RSA) to lock files (`T1486`), leaving behind a ransom note (often a `.txt` or `.hta` file) detailing payment instructions.

Indicators of Compromise & Impact
The primary impact is severe data loss and business interruption. Host-based IoCs include rapid, massive file modification events detected by EDR, the execution of shadow copy deletion commands, the presence of the dropped ransom note, and modified file extensions. Network IoCs may include beaconing to the attacker's Command and Control (C2) server to register the infection and exchange cryptographic keys.

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_SIGRUN {
    meta:
        description = "Detects Sigrun (ransomware)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "sigrun" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Sigrun Activity
id: 6ca29f9e114dab5343202f302cf48215
status: experimental
description: Detects generic indicators of the sigrun malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*sigrun*"
    condition: selection
level: medium

Containment & Response Steps

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

1. IMMEDIATELY disconnect the infected machine from the network (unplug the Ethernet cable/disable Wi-Fi) to prevent the ransomware from traversing mapped network drives.
2. Do not reboot the machine if encryption is actively occurring; capture a memory dump if possible to aid in potential cryptographic analysis.
3. Identify the initial infection vector (e.g., the phishing email) and block it enterprise-wide.
4. Restore systems from verified, offline backups that were completely inaccessible to the infected host.

What to Avoid

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

1. Do not pay the ransom unless absolutely necessary for business continuity; payment funds criminal enterprises and guarantees nothing.
2. Avoid relying solely on local backups or Volume Shadow Copies, as Sigrun explicitly targets and destroys these recovery mechanisms.

References & External Analysis

• Search "sigrun" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: ransomware)

Explore other malware families in the same category:

• Primawega
• Fgarb
• Jumpta
• Jigsawlocker
• Adkubru

Machine-readable

Get this profile as JSON: https://jordanricky1604-ship-it.github.io/malware-families-catalog/api/sigrun.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.