Sigrun
Table of Contents
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 our technical analysis hubs and the official MITRE ATT&CK framework:
| Technique | Name | Tactic | Official Spec |
|---|---|---|---|
T1486 | Data Encrypted for Impact | Impact | ATT&CK ↗ |
T1490 | Inhibit System Recovery (Deleting volume shadow copies) | Impact | ATT&CK ↗ |
T1547.001 | Boot or Logon Autostart Execution | Persistence | ATT&CK ↗ |
T1204.002 | User Execution: Malicious File | Execution | ATT&CK ↗ |
MITRE D3FEND™ Defensive Countermeasures
Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):
| D3FEND ID | Countermeasure Name | Tactic | Countered ATT&CK | Defensive Guidance |
|---|---|---|---|---|
D3-FEA | File Execution Analysis | Harden | T1204.002 | Enforce AppLocker and Windows Defender Application Control (WDAC) to block executable launches from temporary and user-writable directories. |
D3-FAED | File Alteration Early Detection | Detect | T1486 | Deploy canary files and monitor mass rename/encryption I/O spikes to terminate ransomware threads immediately. |
D3-VSS | Volume Shadow & Snapshot Hardening | Harden | T1490 | Block execution of vssadmin.exe and wmic shadowcopy delete; maintain air-gapped immutable backup repositories. |
D3-RPM | Registry Persistence Monitoring | Detect | T1547.001 | Audit and restrict write privileges to user and machine-level Registry Run/RunOnce keys using Endpoint Privilege Management. |
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:
Tier 1 Primitive Artifact Rule (Fast Triage)
Matches raw strings and file markers. Vulnerable to binary repacking and simple obfuscation.
rule MALWARE_WIN_SIGRUN_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Sigrun"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "sigrun" ascii wide nocase
condition:
uint16(0) == 0x5a4d and any of them
}Tier 2 Behavioral Context Rule (Process Chains & Sigma)
Tracks parent-child process anomalies and suspicious scripting telemetry. Resilient against file renames.
title: SystemHelpDesk Detection - Sigrun (Ransomware) Execution & Triage
id: 63e1889d-4bdb-5d23-97a0-abe1b3f00701
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Sigrun 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/sigrun
- 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.t1204_002
- attack.t1547_001
- attack.t1490
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: criticalTier 3 Attribution Fingerprint Rule (High Fidelity)
Deep signature matching distinctive operational fingerprints and payload characteristics.
rule MALWARE_WIN_SIGRUN_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Sigrun 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 = "sigrun" 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.
- IMMEDIATELY disconnect the infected machine from the network (unplug the Ethernet cable/disable Wi-Fi) to prevent the ransomware from traversing mapped network drives.
- Do not reboot the machine if encryption is actively occurring; capture a memory dump if possible to aid in potential cryptographic analysis.
- Identify the initial infection vector (e.g., the phishing email) and block it enterprise-wide.
- 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.
- Do not pay the ransom unless absolutely necessary for business continuity; payment funds criminal enterprises and guarantees nothing.
- 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)
- Search "sigrun" on Any.Run (Sandbox Sandbox)
- Search "sigrun" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is Sigrun and what threat category does it belong to?
Sigrun is classified as a Ransomware. Documented across security telemetry, it is engineered to execute unauthorized operations, establish persistent footholds on target endpoints, and facilitate malicious campaigns targeting enterprise and individual environments.
How does Sigrun establish persistence and evade defensive controls?
Sigrun typically establishes persistence through registry run keys, scheduled tasks, or service installations, while evading signature-based antivirus solutions through code obfuscation, memory injection, or anti-analysis sandbox checks.
What are the essential incident response steps for mitigating a Sigrun compromise?
Security teams responding to Sigrun should immediately isolate affected endpoints from the network, perform memory triage to capture volatile forensic artifacts, audit registry and startup persistence mechanisms, revoke exposed user credentials, and restore systems from verified, clean backups.
What cryptographic algorithms and file targeting techniques does Sigrun employ during execution?
Sigrun typically leverages hybrid cryptographic architectures combining symmetric stream or block ciphers (such as AES-256 or ChaCha20) for rapid file encryption with asymmetric algorithms (such as RSA-2048 or Curve25519) to securely protect the session keys. It aggressively targets sensitive file extensions including corporate documents, databases, virtual disks, and backups while systematically executing commands to delete Volume Shadow Copies (vssadmin delete shadows /all /quiet) and disable system recovery options.
Are decryptors available for Sigrun, and what is the recommended recovery procedure?
Decryption availability for Sigrun depends on whether security researchers or law enforcement (such as the No More Ransom initiative) have recovered the master private keys or discovered flaws in its key generation routines. Victims should never pay the extortion demand, as payment fuels criminal operations without guaranteeing file restoration. The recommended recovery procedure entails isolating infected hosts, conducting forensic disk imaging, identifying the root access vector, and restoring validated systems from immutable offline backups.
How do I remove the Sigrun Ransomware from Windows?
Manual removal of Sigrun is highly discouraged as it may leave persistence mechanisms intact. We recommend disconnecting the device from the internet and utilizing a professional incident response service or enterprise-grade EDR software to conduct a full forensic sweep.
Is Sigrun a virus or a Ransomware?
Sigrun is classified as a Ransomware. Unlike traditional viruses that infect files, modern malware like Sigrun typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.
What are the main symptoms of a Sigrun infection?
Symptoms of Sigrun can include unexpected system slowness, unauthorized outbound network traffic to unknown IP addresses, disabled security software, and suspicious background processes running from AppData or Temp directories.
Protect Your Network Against Ransomwares
Want to prevent Sigrun and similar threats from compromising your organization? Read our comprehensive defensive guide: Ransomware Containment & Incident Response.
📣 Threat Intel Correction or Update?
Notice an outdated IOC, unlisted alias, or disputed attribution? Threat researchers are invited to propose an update on GitHub or contact the SystemHelpDesk research desk. All community revisions are credited in our public CHANGELOG.
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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.