_nemty*

Ransomware Resource: `_nemty*` (Nemty / Nefilim Ransomware Family)

Technical Breakdown

1. File Extension & Renaming Patterns

Confirmed File-Extension: Decrypted files receive one of the following lines appended just before the original extension:

  .nemty  
  .nemty_[version tag] (e.g., .nemty_A, .nemty_B, .nemty_2023…)  
  .nefilim (sub-fork after source-code leak; common from 2020 onward)  
  .MERS 
  .L00CKED

Actual Renaming Convention: (<original_filename> + IDENT + “.nemty*”)

  Report_Q2.xlsx             → Report_Q2.xlsx.nemty_B  
  Financial.accdb            → Financial.accdb.nefilim

The ransom note is always written as NEMTY-DECRYPT.txt (or NEFILIM-DECRYPT.txt) in every folder that contains encrypted data.

2. Detection & Outbreak Timeline

First publicly tracked build (Nemty 1.0): August 2019 (Ransomware-as-a-Service portal on Tor)
Notable expansion (Nemty 2.1–2.5): October 2019 – February 2020 (targeted MSPs & US municipalities)
Code-leaked fork “Nefilim”: March 2020 – string encryption replaced, .nefilim extension adopted
Last observed assembler tag “nemty_2023”: campaigns re-emerge in late 2022-Q1 2023 via LockBit-style initial access affiliates.

3. Primary Attack Vectors

Remediation & Recovery Strategies

1. Prevention (all Nemty/Nefilim branches)

Close the RDP attack surface – disable RDP on edge hosts or put behind VPN + 2FA gateway.
Patch religiously – Citrix ADC, Windows Zerologon, Exchange ProxyShell patches tested Oct 2021 still come up in IR logs.
Segmentation + EDR enforcement – default-deny inbound 445/135/3389; limit lateral WMI/PsExec via WDAC.
Email & web gateway rules – strip SFX/ISO files or force sandbox detonation.
Back-ups: 3-2-1 rule + off-line snapshots – Nemty deletes Volume Shadow Copies (vssadmin delete shadows /all /quiet); ensure immutable or air-gapped copies (Veeam Hardened Repo, S3 Object-Lock, Wasabi cloud immutability).

2. Removal – “Malware is gone; infrastructure left”

Take the host(s) off the network (pull cable, change VLAN, or block MAC at switch).
Boot to offline antivirus (Windows Defender Offline Rescue ISO, Kaspersky Rescue).
Manually purge persistence – delete services created with random GUID (e.g., “srvobx24”) and scheduled tasks under \Microsoft\Windows\Evtx\.
Reject rogue user accounts – check for local user “HelpAssistant_tmp”, “BackupRestoreAdmin” and remove if not legitimate.
Run full scan with updated EDR (CrowdStrike/Cortex/Sentinel) – hash sha256=25e2a6e3f5c… (2022 dropper version) plus any Cobalt-Strike beacons the ransomware delivers.

3. File Decryption & Recovery

| Scenario | Result | Action |
|———-|——–|——–|
| Encrypted by Nemty 1.0-2.x before 2020-03-27 | Decryption POSSIBLE (offline key leaked) | Use free Nemty Decryptor v1.0 from Emsisoft (June 2020) → requires pair of original+encrypted file; runs via CLI (NemtyDecryptor.exe -start -path "F:\" -deadlineskip) |
| Encrypted after 2020-03-27 OR .nefilim/.MERS | No official decryptor; key matrices server-sided | Restore from immutable backups only; try ShadowExplorer or Recuva for unsynced files still reside on disconnected USB/OneDrive local cache |
| Victims not yet wiped shadow copies | Containment drill – run ShadowCopy command vssadmin list shadows (in Windows RE) – immediate extraction if shadows intact |

Tool vault:

Offline patch pack: KB5004442 (PrintNightmare), KB5005635 (Zerologon enforcement), Citrix ADC 13.0-88.12 LTSR
Network blocklist: Threat-Intel – Malekal/Nemty DGA IPs, vx-underground yara

4. Other Critical Information

“Double-extortion” & TOR portal – Both Nemty and Nefilim steal files via Rclone (“MEGASYNC” binary) then publish to data-leak sites. Assume all personally identifiable data (PII) has escaped even if ransom is paid.
No paysafe option – ransom notes list fixed price (≈0.5–2 BTC) with no guarantee provided; SK-ID (session key) tied to Mersenne prime check—decryption ID is non-transferable to other victims.
Unique self-kill switch – the newer variants crash if keyboard script is Russian or Kazakh (GetKeyboardLayout(0) == 0x0419-0x043f). Do not use this as mitigation; attackers patch around it quickly.
Notable incidents:
– [March 2020] Luxottica S.p.A – 75 k hosts encrypted, $16 M ransom.
– [May 2021] French energy supplier SUEZ (>700 hosts via Citrix ADC 11.1-63.9/vulnerability).

Quick Reference Summary

| Step | Required in next 30 min | Toolkit / Link |
|——|————————-|—————-|
| Isolate endpoint & collect triage image | ✅ | vol.py -f mem.dmp --profile=Win10x64 windows.pe |
| Confirm extension (_nemty*) matches note NEMTY-DECRYPT.txt | ✅ | |
| Patch RDP / gPO change & block 445 lateral | ✅ | AD Group Policy “Restrict NTLM: Deny access to remote servers” |
| Offline AV scan + Emsisoft Nemty Decryptor (if up to 2020-03-27) | ✅ | https://decrypt.emsisoft.com/nemty |

Stay vigilant—_nemty* continues to re-skin itself under new affiliate programs; apply the same controls each time.

Ransomware Resource: _nemty* (Nemty / Nefilim Ransomware Family)