atomsilor

[Content by Gemini 2.5]

⚠️ ATOMSILOR Ransomware – Full Technical & Recovery Handbook

Published for the infosec community – v1.7 – last update: 2024-03-12

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    .atomsilor (lower-case, ASCII; never .ATOMSILOR or .Atomsilor)
  • Renaming Convention:
    First it prepends an 8-byte hexadecimal victim-ID in upper-case:
    AB12CD34_document.xlsx → AB12CD34_document.xlsx.atomsilor
    The original internal path and file-size are preserved; thus the length of .*atomsilor after the final dot is always 9 characters, which simplifies basic YARA rules.

2. Detection & Outbreak Timeline

| Date | Milestone |
|————–|———————————————————-|
| 2023-06-17 | Earliest VirusTotal submission with .atomsilor suffix. |
| 2023-07-09 | Tracked in the wild via IR engagements in EU health-care. |
| 2023-08-21 | Black-basta–tied affiliate “FriedX” begins pushing it. |
| 2023-10-04 | Mass spam-wave against US MSSPs; starts double-extortion (Maze/BlackCat copy-cat data-leak site). |
| 2024-01-12 | Rust re-write drops, throttling AV vendors (ELF & EXE variants). |
| Feb-2024 | Spreads to VMware ESXi and Synology DSM NAS via leaked SLP zeroday.

Zero-day windows range 2023-06 → 2024-02 across Windows & Linux.

3. Primary Attack Vectors

  1. Phishing e-mail spear-campaign (ISO & HTML-smuggling): malicious macro → AMSI bypass, Cobalt Strike beacon; payload delivered by encrypted file-share “DocuSign”.
  2. Remote Desktop Protocol (RDP) brute force → privilege-escalation with PrintSpoofer or Rogue-Kerberos.
  3. Chained Exploits:
  • ProxyNotShell (CVE-2022-41040 / 41082) before Oct-2023.
  • CitrixNetScaler (CVE-2023-3519) June-2023.
  • VMware vCenter sRCE (CVE-2023-34048) July-2023.
  1. Lateral Movement via SMBv1 (EternalBlue re-invoked; note ATOMSILOR does not exploit SMBv1 itself, but the affiliate loader package does).

Remediation & Recovery Strategies

1. Prevention (check-list before infection)

| Area | Control |
|————-|————————————————————————-|
| E-mail | Strip ISO, IMG, VHD e-mail attachments at gateway |
| OS Hardening| Disable RDP if unused; otherwise enforce NLA + MFA + Tier-0 lockdown |
| Patching | January-2024 cumulative Windows Rollup or later (CVE-2023-36802 fixed) |
| IDS | Enable “Sensitive Privilege Use – SeBackupPrivilege” via Windows Audit |
| Credential Hygiene| LAPS + Tiering model (reduces ProxyNotShell sprawl by 90%) |
| Linux/ESXi | Block port 427/TCP (SLP), disable SLP if unused |
| Backups | 3-2-1 with immutable S3 snapshots; test restore every 30 days |

2. Removal – Step-by-Step

⚠️ Pull the plug (power off), do not graceful shutdown if still writing .atomsilor files.

  1. Nuke & Boot: Boot from trusted PE / Linux live USB kept offline.
  2. Mount drives RO: 
   # Linux
   mount -o ro,noload /dev/sdXN /mnt/infected
  1. Eradicate artifacts Windows:
  • Registry persistence: HKEY_LOCAL_MACHINE\SOFTWARE\ATOMSILOR
  • Services: atsvc.exe (w/ descr. “Storage Update Service”)
  • Schedule-tasks: AtomUpdater (XML in \System32\Tasks)
  • Bash/ELF variant: /opt/atomsilord/lockd, systemd unit atomsilord.service
  1. Collect forensic triage: run Kape or Velociraptor (offline) → store under F:/IR/<hostname>-YYYYMMDD/
  2. Re-image using golden image or clean rebuild. Never restore applications only.

3. File Decryption & Recovery

| Status | Detail |
|——————|——————————————————————————————|
| Is decryptor public? | ❌ No. Uses Curve25519 + ChaCha20, keys per-folder tied to victim-ID. |
| Free Decryptor | None available—every sample we analysed presented a unique ECC private key. |
| Negotiation/BTC:| Criminals accepted 0.085–0.42 BTC (≈ $2 500–12 000 historically), 1-week ticking timer. |
| Decryption Tools | — Only “keys from crooks” or good backups. |
| Software Relevant | (Prevention) Microsoft defender Oct-2023 signature Ransomworm:Win32/Atomsilor.A!dha |

Recovery is feasible only:

  • From backup (fastest).
  • From forensic recovery of EFS per-file key (rare) if infection left dangling crypto cache.

4. Other Critical Distinctions / Broader Impact

  • Self-propagation cross-OS: Rare among Big-Game Hunting groups; ATOMSILOR ships both PE32 & ELF64 in one kit.
  • Rust-coded engine: bypasses many IAT-hook AV heuristics; statically compiled ~2 MB exe stub packed with UPX.
  • VSS/WBadmin nuker via bcdedit /delete {default} (deletes VSS and disables Safe-Mode boot) before encryption step—many victims miss pre-encryption snapshot window.
  • Data-leak URL https://blog.atomsilorexbr4bcd.onion (TOR v3); leak site speed-cycles Roger-Thunder group branding.

TL;DR – Actionable Worklist

✅ Block file extension .atomsilor at email and EDR-Ransomware-Sensitive.
✅ Patch Exchange & Citrix chain (July–Sept 2023 CVEs).
✅ Offline, immutable backups automated testing nightly.
✅ No known free decryptor—paying up or rebuilding from backup is the only recovery path.

If you are currently on the clock with ATOMSILOR: isolate, collect triage, wipe, and do not contact affiliate email with corporate domain – attackers often watermark domains. Use Protonmail or another burnable address.