Sigma

Overview

Ransom:Win32/Sigma is a severe threat classified as Ransomware. It is designed to extort victims by strongly encrypting critical personal or corporate data, appending a specific extension (often `.sigma` or similar variations) to the files, and demanding payment in cryptocurrency for the decryption key.

Understanding Sigma
To an end-user, a Sigma infection represents an immediate crisis: documents and databases are suddenly inaccessible, and a ransom note (often a `.txt` or `.hta` file) is presented on the desktop. For an enterprise, it triggers a 'Code Red' incident response, requiring immediate network isolation to prevent lateral movement and the encryption of enterprise file shares and backups.

Execution and Extortion Mechanics
Sigma is frequently distributed via targeted phishing (`T1566.001`), exploit kits, or dropped by other initial access malware. Upon execution, it achieves persistence (`T1547.001`) and actively attempts to impair endpoint defenses (`T1562.001`). Crucially, before encryption begins, it executes commands like `vssadmin.exe delete shadows /all /quiet` to destroy Windows Volume Shadow Copies, preventing easy system restoration (`T1490`). It then rapidly iterates through the filesystem and mapped network drives, encrypting files matching high-value extensions (e.g., `.docx`, `.sql`, `.pdf`) using robust encryption algorithms (`T1486`).

Indicators of Compromise & Impact
The impact is catastrophic data loss. Host-based IoCs include massive spikes in disk I/O and CPU usage during the encryption phase, the sudden appearance of ransom note files in every directory, and EDR alerts for `vssadmin.exe` or `wmic.exe` attempting to delete shadow copies. Network IoCs may include anomalous outbound traffic if the ransomware incorporates a data exfiltration module.

MITRE ATT&CK Techniques

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

Tactical Mitigations

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

• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

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

Sigma Rule

title: Suspicious Sigma Activity
id: e773536932c61c7ee11944cefde49e30
status: experimental
description: Detects generic indicators of the sigma malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*sigma*"
    condition: selection
level: medium

Containment & Response Steps

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

1. Immediately physically disconnect the infected endpoint from the network (pull the Ethernet cable) to stop the ransomware from encrypting network shares and spreading laterally.
2. Do NOT reboot the infected machine; if possible, capture a live memory image (RAM dump) as the encryption keys might temporarily reside in memory.
3. Restore the encrypted systems from secure, offline backups that were isolated from the network at the time of the attack.
4. Verify the integrity of Active Directory; ransomware is often deployed network-wide by attackers who have already compromised Domain Admin credentials.

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 immediately; paying funds criminal syndicates, and there is no guarantee the provided decryptor will actually work.
2. Avoid reconnecting restored machines to the network until the initial entry vector has been completely secured.

References & External Analysis

• Search "sigma" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: ransomware)

Explore other malware families in the same category:

• Walerlop
• Tarayt
• Tspy
• Trpctrooper
• Axbn

Machine-readable

Get this profile as JSON: https://jordan123234-malware-families-explorer.static.hf.space/api/sigma.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.