--- name: eradicating-malware-from-infected-systems-6c0b752f9686 description: Systematically remove malware, backdoors, and attacker persistence mechanisms from infected systems while ensuring complete eradication and preventing re-infection. domain: cybersecurity subdomain: incident-response tags: - incident-response - eradication - malware-removal - persistence - dfir mitre_attack: - T1486 - T1490 - T1070 - T1078 - T1547 version: '1.0' author: mahipal license: Apache-2.0 nist_csf: - RS.MA-01 - RS.MA-02 - RS.AN-03 - RC.RP-01 --- # Eradicating Malware from Infected Systems ## When to Use - Malware infection confirmed and containment is in place - Forensic investigation has identified all persistence mechanisms - All compromised systems have been identified and scoped - Ready to remove attacker artifacts and restore clean state - Post-containment phase requires systematic cleanup ## Prerequisites - Completed forensic analysis identifying all malware artifacts - List of all compromised systems and accounts - EDR/AV with updated signatures deployed - YARA rules for the specific malware family - Clean system images or verified backups for restoration - Network isolation still in effect during eradication ## Workflow ### Step 1: Map All Persistence Mechanisms ```bash # Windows - Check all known persistence locations # Autoruns (Sysinternals) - comprehensive autostart enumeration autorunsc.exe -accepteula -a * -c -h -s -v > autoruns_report.csv # Registry Run keys reg query "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /s reg query "HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /s reg query "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce" /s reg query "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Explorer\Run" /s # Scheduled tasks schtasks /query /fo CSV /v > schtasks_all.csv # WMI event subscriptions Get-WMIObject -Namespace root\Subscription -Class __EventFilter Get-WMIObject -Namespace root\Subscription -Class CommandLineEventConsumer Get-WMIObject -Namespace root\Subscription -Class __FilterToConsumerBinding # Services Get-Service | Where-Object {$_.Status -eq 'Running'} | Select-Object Name, DisplayName, BinaryPathName # Linux persistence cat /etc/crontab ls -la /etc/cron.*/ ls -la /etc/init.d/ systemctl list-unit-files --type=service | grep enabled cat /etc/rc.local ls -la ~/.bashrc ~/.profile ~/.bash_profile ``` ### Step 2: Identify All Malware Artifacts ```bash # Scan with YARA rules specific to the malware family yara -r -s malware_rules/specific_family.yar C:\ 2>/dev/null # Scan with multiple AV engines # ClamAV scan clamscan -r --infected --remove=no /mnt/infected_disk/ # Check for known malicious file hashes find / -type f -newer /tmp/baseline_timestamp -exec sha256sum {} \; 2>/dev/null | \ while read hash file; do grep -q "$hash" known_malicious_hashes.txt && echo "MALICIOUS: $file ($hash)" done # Check for web shells find /var/www/ -name "*.php" -newer /tmp/baseline -exec grep -l "eval\|base64_decode\|system\|passthru\|shell_exec" {} \; # Check for unauthorized SSH keys find / -name "authorized_keys" -exec cat {} \; 2>/dev/null ``` ### Step 3: Remove Malware Files and Artifacts ```bash # Remove identified malicious files (after forensic imaging) # Windows Remove-Item -Path "C:\Windows\Temp\malware.exe" -Force Remove-Item -Path "C:\Users\Public\backdoor.dll" -Force # Remove malicious scheduled tasks schtasks /delete /tn "MaliciousTaskName" /f # Remove WMI persistence Get-WMIObject -Namespace root\Subscription -Class __EventFilter -Filter "Name='MalFilter'" | Remove-WMIObject Get-WMIObject -Namespace root\Subscription -Class CommandLineEventConsumer -Filter "Name='MalConsumer'" | Remove-WMIObject # Remove malicious registry entries reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v "MalEntry" /f # Remove malicious services sc stop "MalService" && sc delete "MalService" # Linux - Remove malicious cron entries, binaries, SSH keys crontab -r # Remove entire crontab (or edit specific entries) rm -f /tmp/.hidden_backdoor sed -i '/malicious_key/d' ~/.ssh/authorized_keys systemctl disable malicious-service && rm /etc/systemd/system/malicious-service.service ``` ### Step 4: Reset Compromised Credentials ```bash # Reset all compromised user passwords Import-Module ActiveDirectory Get-ADUser -Filter * -SearchBase "OU=CompromisedUsers,DC=domain,DC=com" | Set-ADAccountPassword -Reset -NewPassword (ConvertTo-SecureString "TempP@ss!$(Get-Random)" -AsPlainText -Force) # Reset KRBTGT password (twice, 12+ hours apart for Kerberos golden ticket attack) Reset-KrbtgtPassword -DomainController DC01 # Wait 12+ hours, then reset again Reset-KrbtgtPassword -DomainController DC01 # Rotate service account passwords Get-ADServiceAccount -Filter * | ForEach-Object { Reset-ADServiceAccountPassword -Identity $_.Name } # Revoke all Azure AD tokens Get-AzureADUser -All $true | ForEach-Object { Revoke-AzureADUserAllRefreshToken -ObjectId $_.ObjectId } # Rotate API keys and secrets # Application-specific credential rotation ``` ### Step 5: Patch Vulnerability Used for Initial Access ```bash # Identify and patch the entry point vulnerability # Windows Update Install-WindowsUpdate -KBArticleID "KB5001234" -AcceptAll -AutoReboot # Linux patching apt update && apt upgrade -y # Debian/Ubuntu yum update -y # RHEL/CentOS # Application-specific patches # Update web application frameworks, CMS, etc. # Verify patch was applied Get-HotFix -Id "KB5001234" ``` ### Step 6: Validate Eradication ```bash # Full system scan with updated signatures # CrowdStrike Falcon - On-demand scan curl -X POST "https://api.crowdstrike.com/scanner/entities/scans/v1" \ -H "Authorization: Bearer $FALCON_TOKEN" \ -H "Content-Type: application/json" \ -d '{"ids": ["device_id"]}' # Verify no persistence mechanisms remain autorunsc.exe -accepteula -a * -c -h -s -v | findstr /i "unknown verified" # Check for any remaining suspicious processes Get-Process | Where-Object {$_.Path -notlike "C:\Windows\*" -and $_.Path -notlike "C:\Program Files*"} # Verify no unauthorized network connections Get-NetTCPConnection -State Established | Where-Object {$_.RemoteAddress -notlike "10.*" -and $_.RemoteAddress -notlike "172.16.*"} | Select-Object LocalPort, RemoteAddress, RemotePort, OwningProcess # Run YARA rules again to confirm no artifacts remain yara -r malware_rules/specific_family.yar C:\ 2>/dev/null ``` ## Key Concepts | Concept | Description | |---------|-------------| | Persistence Mechanism | Method attacker uses to maintain access across reboots | | Root Cause Remediation | Fixing the vulnerability that enabled initial compromise | | Credential Rotation | Resetting all potentially compromised passwords and tokens | | KRBTGT Reset | Invalidating Kerberos tickets after golden ticket attack | | Indicator Sweep | Scanning all systems for known malicious artifacts | | Validation Scan | Confirming eradication was successful before recovery | | Re-imaging | Rebuilding systems from clean images rather than cleaning | ## Tools & Systems | Tool | Purpose | |------|---------| | Sysinternals Autoruns | Enumerate all Windows autostart locations | | YARA | Custom rule-based malware scanning | | CrowdStrike/SentinelOne | EDR-based scanning and remediation | | ClamAV | Open-source antivirus scanning | | PowerShell | Scripted cleanup and validation | | Velociraptor | Remote artifact collection and remediation | ## Common Scenarios 1. **RAT with Multiple Persistence**: Remote access trojan using registry, scheduled task, and WMI subscription. Must remove all three persistence mechanisms. 2. **Web Shell on IIS/Apache**: PHP/ASPX web shell in web root. Remove shell, audit all web files, patch application vulnerability. 3. **Rootkit Infection**: Kernel-level rootkit that survives cleanup. Requires full re-image from known-good media. 4. **Fileless Malware**: PowerShell-based attack living in memory and registry. Remove registry entries, clear WMI subscriptions, restart system. 5. **Active Directory Compromise**: Attacker created backdoor accounts and golden tickets. Reset KRBTGT, remove rogue accounts, audit group memberships. ## Output Format - Eradication action log with all removed artifacts - Credential rotation confirmation report - Vulnerability patching verification - Post-eradication validation scan results - Systems cleared for recovery phase --- Source attribution: 26zl Original project: https://github.com/26zl/cybersec-toolkit/blob/2ad2519d437cda1f8a822ef7adc336993601a5ac/.claude/skills/eradicating-malware-from-infected-systems/SKILL.md License: Apache-2.0 License information: https://www.apache.org/licenses/LICENSE-2.0 Original upstream instructions; downloaded from Mega AI Hub. ## Upstream license notice Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. Definitions. "License" shall mean the terms and conditions for use, reproduction, and distribution as defined by Sections 1 through 9 of this document. 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See the License for the specific language governing permissions and limitations under the License. # Mega AI Hub resource metadata Creator / publisher: 26zl Original project: https://github.com/26zl/cybersec-toolkit/blob/2ad2519d437cda1f8a822ef7adc336993601a5ac/.claude/skills/eradicating-malware-from-infected-systems/SKILL.md Attribution basis: Source repository record Fields of work: Development & Engineering Roles: Security Engineer Specialties: Backend Tools: Autoruns Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: e41c6bbf8bf628e691064d9269706dd6a805b89bba379c29ac7431b7587aa233