From cybersecurity-skills
Detects ransomware kill switches via mutexes, domains, and registry checks. Implements mutex vaccination and DNS monitoring to block execution during analysis or incident response.
npx claudepluginhub mukul975/anthropic-cybersecurity-skills --plugin cybersecurity-skillsThis skill uses the workspace's default tool permissions.
- Analyzing a ransomware sample to determine if it contains a kill switch mechanism (mutex, domain, registry)
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Do not use kill switch vaccination as a primary defense. Not all ransomware families implement kill switches, and those that do may remove them in newer versions. This is a supplementary detection and prevention layer.
ctypes (Windows) for mutex creation and enumerationAnalyze samples for common kill switch patterns:
Kill Switch Types Found in Ransomware:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
1. MUTEX-BASED (most common):
- Ransomware creates a named mutex at startup
- If mutex already exists → another instance is running → exit
- Defense: Pre-create the mutex to prevent execution
- Examples:
WannaCry: Global\MsWinZonesCacheCounterMutexA
Conti: kasKDJSAFJauisiudUASIIQWUA82
REvil: Global\{GUID-based-on-machine}
Ryuk: Global\YOURPRODUCT_MUTEX
2. DOMAIN-BASED:
- Ransomware resolves a hardcoded domain before executing
- If domain resolves → security sandbox detected → exit
- Defense: Register/sinkhole the domain to activate kill switch
- Examples:
WannaCry v1: iuqerfsodp9ifjaposdfjhgosurijfaewrwergwea.com
WannaCry v1: fferfsodp9ifjaposdfjhgosurijfaewrwergwea.com
3. REGISTRY-BASED:
- Check for specific registry key/value before executing
- If key exists → exit (anti-analysis or kill switch)
- Defense: Create the registry key proactively
4. FILE-BASED:
- Check for existence of specific file or directory
- If marker file exists → exit
- Defense: Create the marker file on all endpoints
5. LANGUAGE-BASED:
- Check system language/keyboard layout
- Exit if Russian/CIS country keyboard detected
- Common in Eastern European ransomware groups
Pre-create known ransomware mutexes on endpoints to prevent execution:
# Windows mutex vaccination using ctypes
import ctypes
from ctypes import wintypes
kernel32 = ctypes.WinDLL('kernel32', use_last_error=True)
def create_mutex(name):
"""Create a named mutex to vaccinate against ransomware."""
handle = kernel32.CreateMutexW(None, False, name)
error = ctypes.get_last_error()
if handle == 0:
return False, f"Failed to create mutex: error {error}"
if error == 183: # ERROR_ALREADY_EXISTS
return True, f"Mutex already exists (already vaccinated): {name}"
return True, f"Mutex created successfully: {name}"
KNOWN_RANSOMWARE_MUTEXES = [
"Global\\MsWinZonesCacheCounterMutexA", # WannaCry
"Global\\kasKDJSAFJauisiudUASIIQWUA82", # Conti
"Global\\YOURPRODUCT_MUTEX", # Ryuk variant
"Global\\JhbGjhBsSQjz", # Maze
"Global\\sdjfhksjdhfsd", # Generic ransomware
]
Use Sysmon to detect when ransomware creates its characteristic mutexes:
<!-- Sysmon configuration for mutex monitoring -->
<Sysmon schemaversion="4.90">
<EventFiltering>
<!-- Event ID 1: Process creation with mutex indicators -->
<ProcessCreate onmatch="include">
<CommandLine condition="contains">mutex</CommandLine>
<CommandLine condition="contains">CreateMutex</CommandLine>
</ProcessCreate>
</EventFiltering>
</Sysmon>
Detection via Event Logs:
━━━━━━━━━━━━━━━━━━━━━━━━
Windows Security Log:
Event ID 4688: Process creation (enable command line logging)
Sysmon:
Event ID 1: Process create (includes command line and hashes)
Event ID 17: Pipe created (named pipes, similar to mutexes)
PowerShell detection:
Event ID 4104: Script block logging (detect mutex creation in scripts)
Velociraptor artifact:
Windows.Detection.Mutants - Enumerates all named mutant objects
Detect ransomware domain-based kill switch resolution attempts:
DNS Monitoring for Kill Switch Domains:
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1. Monitor DNS queries for known kill switch domains
2. High-entropy domain names (>4.0 entropy in domain label) may indicate
ransomware kill switch domains or DGA-generated C2 domains
3. Queries to newly registered domains from endpoints that typically
only access well-established domains
Indicators:
- Domain with no prior resolution history
- Domain registered in last 24-72 hours
- High character entropy in domain name
- Resolution attempt followed by either mass encryption (kill switch failed)
or process termination (kill switch activated)
During an active incident, scan endpoints for ransomware-associated mutexes:
# PowerShell: List all named mutant objects using Sysinternals Handle
# handle.exe -a -p <PID> | findstr "Mutant"
# Velociraptor query for mutex hunting:
# SELECT * FROM glob(globs="\\BaseNamedObjects\\*") WHERE Name =~ "mutex_pattern"
# Python-based enumeration (requires pywin32):
# import win32event
# handle = win32event.OpenMutex(0x00100000, False, "Global\\MutexName")
| Term | Definition |
|---|---|
| Mutex (Mutant) | A Windows kernel synchronization object used to ensure only one instance of a program runs; ransomware uses named mutexes to prevent re-infection |
| Kill Switch | A mechanism in ransomware that causes it to terminate without encrypting if a specific condition is met (mutex exists, domain resolves, file present) |
| Mutex Vaccination | Proactively creating named mutexes on endpoints that match known ransomware mutex names, preventing the ransomware from executing |
| Domain Sinkhole | Registering or redirecting a malicious domain to a controlled server; used to activate domain-based kill switches |
| DGA (Domain Generation Algorithm) | Algorithm used by malware to generate pseudo-random domain names for C2 communication, sometimes incorporating kill switch checks |