doppelpaymer

[Content by Gemini 2.5]

DoppelPaymer Ransomware – Comprehensive Technical & Recovery Guide

Compiled for defenders, responders, and the wider community

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    • .locked is the primary appended extension.
    • Numbered extensions (.locked1, .locked2, .locked3,…) appear on successive attacks to track campaign waves.
  • Renaming Convention:
    Files: original-name.ext.locked
    e.g., Report.xlsx becomes Report.xlsx.locked
    Shares: Same pattern across all mapped drives and discovered resources.
    Attackers also drop a ransom note readme.README.txt (or README_LOCKED.txt) in every directory and usually on the desktop/root of shares.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    • June 2019 – First public sightings emerged on BleepingComputer and ID-Ransomware.
    • Peak Activity: October 2019 – January 2021.
    • Tapering: After the Emotet takedown (January 2021) and improved defenses the volume declined, but new waves continued until Europol & FBI’s Operation Cyclone arrested key operators (February 2021). Sporadic resurfacing is observed when operators reinstate infrastructure under new TTPs.

3. Primary Attack Vectors

DoppelPaymer is human-operated, post-exploitation ransomware leveraging multiple entry points:

  1. Emotet → Dridex → Cobalt Strike kill-chain – Most common.
    • Emotet malspam drops Dridex banking trojan.
    • Dridex downloads Cobalt Strike beacon.
    • Cobalt Strike hands off to DoppelPaymer payload.

  2. Malicious RDP access (brute-forced, abused exposed 3389, Phanguling).
    • Often preceded by credential-stuffing from earlier breaches (Collection#1, #2).
    • Attacker achieves elevated RDP session, runs dopplecomp.exe, dopple32-msi.exe, or PowerShell implant.

  3. Unpatched servers – Mainly:
    • CVE-2019-19781 – Citrix ADC & Gateway (vulnerability disclosure Dec 17 2019).
    • BlueKeep CVE-2019-0708 – RDP remote code execution (older but still seen until 2020).
    • ProxyLogon chain (CVE-2021-26855 and siblings) although these are more recent than original peak.

  4. Tooling & Privilege Escalation assists:
    • MimiKatz – credential dumping from LSASS/memory.
    • ProcessHacker / GMER – AV/EDR killing.
    • PsExec & WMIC for lateral movement.

Remediation & Recovery Strategies:

1. Prevention

Essential preventive hardening:

  • Patch immediately: Citrix ADC, RDS Gateway, Exchange, SMBv1-disabled OS.
  • Disable legacy protocols:
    • SMBv1 (Server Registry: HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters | SMB1 = 0).
    • Block RDP from the internet if possible or tunnel via VPN with MFA.
  • Restrict powershell.exe and cmd.exe execution: Use Windows Defender/ASR rules or AppLocker policies to whitelist authorized scripts.
  • Email filtering:
    • SPF + DKIM + DMARC against Emotet.
    • Macro blocking for Office documents from external senders.
  • MFA for service & domain admin accounts.
  • Network Segmentation & EDR visibility.
  • Offline encrypted backups that cannot be reached through observed net use /delete tactics.

2. Removal

Step-by-step cleanup for infected PCs/Servers:

  1. Physically isolate affected systems; pull network cables or disable adapters at hypervisor level.
  2. Power down suspected storage hosts to mitigate additional encryption.
  3. Boot into Safe Mode or WinRE and use a clean offline Windows PE/WinPE USB to inspect OS.
  4. Enumerate persistence:
    • Registry: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SerCxFLT, RunOnce keys.
    • Scheduled Tasks named iprep or UpdateSystemHelper.
  5. Delete malicious binaries wherever renamed (default names:
    %TEMP%\[random]\dopplecomp.exe, %WINDIR%\System32\dopple*.exe).
  6. Remove Cobalt-Strike/Emotet beacons (watch for base64-encoded PowerShell from %WINDIR%\Fonts\ directory).
  7. Revert malicious GPO/ACL changes on shared folders (icacls C:\Data /reset).
  8. Re-image the OS partition once forensic triage is complete.

(Use Microsoft Defender Offline/Intune Cloud-Delivered Protection, Bitdefender GravityZone Rescue, or ESET SysRescue Live when volume-shrinking the C: drive.)

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Decryption WITHOUT paying is impossible for most strains—DoppelPaymer shipped both a locally-stored asymmetrical RSA-2048/4096 master public key and AES-256 per-file key pairs. The private key never touches the victim environment.
    • Exception: On July 11 2020 the DoppleLeaks administrator leaked the master private key for one campaign branch (Found156729e66…) with 15 000+ victims.
    – A decryptor compiled by BleepingComputer + Emsisoft (doppledec.exe) will decrypt only the files encrypted before July 2020 campaign repositories are rekeyed repeatedly).
    – Check ransomware ID services (https://id-ransomware.malwarehunterteam.com) and PCRisk tool for that narrow scenario.
  • Essential Tools & Patches:
    • CrowdStrike’s DoveTail DoppelPaymer-detect YARA rules (Q1 2020).
    • Microsoft’s KB4538483/ KB4499164: ensure Exchange has April 2020 cumulative updates.
    • AnyConnect Secure Client ASA patch for VPN bypass leaks.
    • Domain Controllers: KB4499164 + protect from Zerologon (CVE-2020-1472) which attackers used to rubber-stamp DoppelPaymer domain admin rights.
    • CISA & FBI joint alert TA20-280A – IOCs and IP/domain blocklists still relevant for legacy infrastructure.

4. Other Critical Information

  • Rebranding Trend:
    • After arrests in 2021 several affiliates moved to LockBit 2.0 and TeslaCrypt-Nunov franchising while reusing the TeamViewer/DarkComet rewrite standards.
  • Double-Extortion & “DoppelLeaks”:
    • Exfiltration framework muhstik used Mega.nz & ISC-FTP to steal data prior to encryption. Victims who refused payment had filenames posted on the public DoppelLeaks Tor site (until February 2021).
  • Notable Impacts:
    • Fresenius Group – Europe’s largest private hospital operator; dialysis devices taken offline in May 2020.
    • Garmin – multimillion-dollar ransom allegedly paid through Arete IR even if denied.
    • DHB-Wernsdorf (Germany) – Emergency transports redirected at peak COVID-19 surge.
  • Unique Command-line flags:
    • -network_only – encrypt network shares only (shipped Oct 2020).
    • -safe – skip predefined anti-crash directories (e.g., C:\Windows).

Quick Reference for the Heat-of-Battle

Emergency Actions (30-second checklist):

  1. Disable any %TEMP%\dopplecomp.exe or %WINDIR%\System32\dopple*.exe scheduled tasks.
  2. Check eventvwr.msc under System Log IDs 4674 (service execution) for unusual shell32.dll launch from C:\perflogs.
  3. Run bcdedit /delete "%wild%" if you see the boot-load injecting SerCx.sys driver (driver-level disk encryption).
  4. If nothing critical is lost – wipe and reinstall. DoppelPaymer removes Shadow Copies (vssadmin delete shadows /all /quiet) but does not touch **Windows Backup (image)` or *Macrium/Acronis offline images*.

Stay vigilant, patch promptly, and never negotiate—the only long-term solution is resilient backups, layered defenses, and skilled incident response.