Grandcrab
Table of Contents
Overview
Ransomware:Win32/GandCrab (often detected as GrandCrab) is one of the most historically significant Ransomware-as-a-Service (RaaS) operations to ever exist. Active primarily from early 2018 to mid-2019, the GandCrab operators claimed to have extorted over $2 billion before formally announcing their 'retirement.' GandCrab pioneered the highly structured, affiliate-based RaaS business model, where core developers maintained the malware and payment portals, while 'affiliates' were responsible for breaching networks (`T1190`) and deploying the payload in exchange for a percentage of the ransom (`T1486`).
Understanding GandCrab (The Rise of RaaS)
To an infected organization, GandCrab was devastating, encrypting servers and demanding payment via Dash or Bitcoin on a Tor-hosted portal. For threat intelligence analysts, GandCrab represents the industrialization of ransomware. When the operators 'retired', the affiliate network did not vanish; highly credible evidence suggests the core team and top affiliates immediately transitioned to form the notorious REvil (Sodinokibi) cartel.
Execution and Evasion Mechanics
Because GandCrab relied on affiliates, the initial access vectors varied wildly: RDP brute-forcing (`T1133`), massive malspam campaigns (often using Emotet or Trickbot loaders) (`T1566.001`), and exploit kits (like RIG and GrandSoft). Once on a network, affiliates utilized tools like Cobalt Strike and BloodHound for lateral movement. The GandCrab executable itself utilized custom packing and 'process hollowing' (`T1055.012`) to evade AV. It terminated database and backup processes (`T1490`) before using Salsa20 and RSA-2048 to encrypt files, appending extensions like `.GDCB`, `.CRAB`, or a randomized string depending on the version.
Indicators of Compromise & Impact
The impact was catastrophic data loss and severe business interruption. Host-based IoCs include files appended with the GandCrab extensions, the presence of ransom notes (e.g., `GANDCRAB-DECRYPT.txt`), and the execution of commands designed to delete Volume Shadow Copies (`vssadmin.exe delete shadows /all /quiet`). Network IoCs include connections to known GandCrab Tor domains via the Tor proxy network for payment negotiation.
MITRE ATT&CK Techniques
Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:
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-PHA | Process Hollowing Analysis | Detect | T1055.012 | Inspect unbacked executable memory regions (PAGE_EXECUTE_READWRITE) for replaced PE image headers inside legitimate host processes. |
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. |
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_GRANDCRAB_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Grandcrab"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "grandcrab" 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 - Grandcrab (Ransomware) Execution & Triage
id: c33ac0b4-9ea0-51a2-b071-1de06a374a2c
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Grandcrab 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/grandcrab
- 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.t1490
- attack.t1486
- attack.t1055_012
- attack.t1133
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_GRANDCRAB_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Grandcrab 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 = "grandcrab" 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 isolate infected hosts to prevent lateral movement and the encryption of network shares.
- Determine the specific version of GandCrab; free decryptors developed by Bitdefender and Europol (NoMoreRansom) are available for versions 1, 4, and 5 through 5.2.
- Conduct a full forensic investigation to determine the affiliate's entry point (e.g., compromised RDP, phishing) to prevent re-infection.
- Restore data from offline, immutable backups if a free decryptor is unavailable or fails.
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; the operators are formally 'retired', and paying funds organized crime. Use the free decryptors.
- Avoid restoring backups without first identifying and closing the initial access vector used by the affiliate.
References & External Analysis
- Search "grandcrab" on VirusTotal (External Analysis)
- Search "grandcrab" on Any.Run (Sandbox Sandbox)
- Search "grandcrab" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is Grandcrab and what threat category does it belong to?
Grandcrab 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 Grandcrab establish persistence and evade defensive controls?
Grandcrab 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 Grandcrab compromise?
Security teams responding to Grandcrab 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 Grandcrab employ during execution?
Grandcrab 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 Grandcrab, and what is the recommended recovery procedure?
Decryption availability for Grandcrab 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 Grandcrab Ransomware from Windows?
Manual removal of Grandcrab 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 Grandcrab a virus or a Ransomware?
Grandcrab is classified as a Ransomware. Unlike traditional viruses that infect files, modern malware like Grandcrab typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.
What are the main symptoms of a Grandcrab infection?
Symptoms of Grandcrab 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 Grandcrab 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.
Machine-readable
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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.