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Detects and exploits ransomware kill switch mechanisms (mutex, domain, registry) and implements proactive mutex vaccination to prevent execution. Useful during malware analysis or incident response for WannaCry-style threats.
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/cybersecurity-skills:implementing-ransomware-kill-switch-detectionThe summary Claude sees in its skill listing — used to decide when to auto-load this skill
- Analyzing a ransomware sample to determine if it contains a kill switch mechanism (mutex, domain, registry)
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:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
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 |
npx claudepluginhub costrict-plugins-repo/mukul975-anthropic-cybersecurity-skills-cybersecurity-skillsDetects and exploits ransomware kill switch mechanisms including mutex, domain, and registry checks. Implements proactive vaccination and monitoring to prevent ransomware execution.
Detects and exploits ransomware kill switch mechanisms including mutex, domain, and registry checks. Implements proactive vaccination and monitoring to prevent ransomware execution.
Detects ransomware kill switches via mutexes, domains, and registry checks; implements mutex vaccination and domain monitoring to prevent execution. For malware analysis and incident response.