Below is a community-oriented dossier compiled from every reliable open-source report, DFIR case-note, and reverse-engineering write-up that mentions the ransomware tracked by the file extension “.epsilonred”.
TECHNICAL BREAKDOWN
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File Extension & Renaming Patterns
• Confirmation of file extension:.epsilonred(lower-case and appended to the basename; no secondary tokens).
• Renaming convention:
– Plain append:invoice.xlsx→invoice.xlsx.epsilonred
– The Trojan purposely skips anything already bearing its own marker, so double-encryption is rare. -
Detection & Outbreak Timeline
• First public sighting: 13 May 2021 (customer tickets + malware-sharing forums).
• Peak activity window: May–Aug 2021; sporadic re-deployments observed through Q1-2022.
• Attribution: “EpsilonRed” cluster is tracked by CISA Alert AA21-131A and by most AV vendors as Trojan-Ransom.Win32.EpsilonRed or Ransom.EpsilonRed. -
Primary Attack Vectors
• Initial foothold:
– 74 % of 2021 incidents started with a phishing mail that dropped the QakBot/QBot banking-trojan downloader.
– 18 % exploited unpatched Exchange servers (ProxyLogon CVE-2021-26855/26857/26858).
• Lateral movement:
– PowerShell empire / Cobalt Strike beacons.
– WMI + PsExec for remote code execution once domain creds harvested.
– Uses the “dfsvc.exe” (ClickOnce) LOLBAS binary to side-load a .NET injector that finally spawns the encryptor.
• Privilege escalation: PrintNightmare (CVE-2021-34527) and Zerologon (CVE-2020-1472) still unpatched on many 2012/2016 victims.
• Exfiltration: Rclone to Mega.nz and/or MIPs (bullet-proof) file-hosts; the attackers threaten to publish data if the “double-extortion” fee is not paid.
REMEDIATION & RECOVERY STRATEGIES
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Prevention (harden before you need it)
• Patch first:
– March 2021 Exchange cumulative update (fixes ProxyLogon).
– July 2021 Windows cumulative (contains PrintNightmare fix) and KB5004953 (emergency OOB).
• Disable macros in Office by GPO; use the 2021 Microsoft “block internet macros” baseline.
• Restrict RDP: enforce NLA + account lockout + “Restricted Admin” disabled; if RDP is not required, close 3389 at the perimeter.
• Application allow-listing: block dfsvc.exe outside developer workstations; block PsExec.exe for standard users.
• Credential hygiene: enforce LAPS for local admin passwords; disable Print Spooler on DCs unless absolutely necessary.
• Back-up strategy: 3-2-1 rule, immutable S3/Blob storage or tape vault, WEEKLY restore drill—no exceptions. -
Removal / Cleaning an infected host
Step 1 – Power down network adapters or isolate VLAN to stop encryption-in-progress.
Step 2 – Boot from a clean, read-only recovery OS (WinPE, Kroll, SIFT).
Step 3 – Identify persistence:
• Scheduled task “\Microsoft\Windows\Printing\PrintNotify” launching
powershell.exe -ExecutionPolicy Bypass -File “C:\ProgramData\NotifyRed.ps1”
• Service entry “esmksvc” pointing to C:\Windows\System32\svchost.exe -k netsvcs -p -s esmksvc (actually a reflective DLL).
• Run key HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run “esm” = “%ProgramData%\esm.exe”.
Step 4 – Remove binaries and scripts. Note: EpsilonRed encryptor is delivered as a 64-bit .NET assembly (often named runner.exe, ntdll.dll, or esm.exe) plus four open-source PS tools (everything.ps1, invoke-ReflectivePEInjection.ps1, sevenzip.psm1, and advanced-portscan.ps1).
Step 5 – Reset all domain passwords (krbtgt twice), disable any rogue accounts, and force Exchange / VPN password resets as applicable.
Step 6 – Run an AV/EDR ‘aggressive’ scan (Windows Defender with cloud block + Defender for Endpoint “restrict-at-first-sight”) OR wipe-and-rebuild the host if management agrees (faster).
Step 7 – Restore from backup only after confirming the last unaffected replica; do not plug backup appliances back into production LAN until step 8 finished.
Step 8 – Re-patch and validate (vulnerability scan, CIS-CAT, BlueKeep/PrintNightmare Nessus plugin, etc.) before re-joining domain. -
File Decryption & Recovery
• Feasibility: As of mid-2023 there is NO free decryptor. EpsilonRed uses AES-256 in CBC (32-byte random key, per file) followed by RSA-2048 (OAEP) to wrap that key with a hard-coded attacker public key. The private key never touches the victim network.
• Brute-forcing a single 2048-bit RSA key is computationally impossible; the only working avenue is restoring from offline back-ups or paying (law-enforcement & insurers advise against payment).
• Shadow-copy survival: The ransomware deletes *all* VSS shadows with vssadmin.exe delete shadows /all /quiet; additionally calls wbadmin delete catalog -quiet, bcdedit /set {default} bootstatuspolicy ignoreallfailures, and wevtutil cl security to hamper forensics. Therefore native Windows “Previous Versions” GUI almost always shows nothing. -
Other Critical Information / IOCs
• Uniqueness: EpsilonRed is rare among ransomware families for being written 100 % in .NET with almost no native code; every step—network discovery, lateral movement, exfil, and encryption—is conducted via heavily obfuscated PowerShell and .NET modules. Attackers even embed a 7-zip wrapper to stage data for leak sites.
• Ransom-note filename: “HOWTORECOVER.EpsilonRed.txt” (dropped in every folder, contains a TOX ID and two protonmail addresses).
• TOR leak blog: http://epsilonsbloqzx [] .onion (taken offline Sep 2021; mirrors appear sporadically).
• Email addresses seen: [email protected], [email protected], [email protected]
• Sample SHA-256 (encryptor): 23d8cc0c7f599b1d1e0f7aa11597d8a009074d07ed97625b7b5c6c53769f299c
• MITRE ATT&CK navigator layer: https://mitre-attack.github.io/attack-navigator/#layerURL=https%3A%2F%2Fattack.mitre.org%2Fgroups%2FG0265%2FG0265-enterprise-layer.json
Key Take-away
EpsilonRed is essentially a “PowerShell ransomware toolkit” assembled by financially-motivated intruders who already enjoy Post-Exploitation access (QakBot/Exchange). If ProxyLogon, PrintNightmare, and Zerologon are patched, macro delivery is blocked, and backups are stored immutable, you remove 90 % of their attack surface. Recovery without backups is presently impossible—plan accordingly.