atom

[Content by Gemini 2.5]

# ATOM RANSOMWARE – COMMUNITY RESOURCE

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .atom (lower-case, always appended after the last dot).
  • Renaming Convention:
  • Original name: Budget_Q2.xlsx
  • After encryption: Budget_Q2.xlsx.atom
  • Nested folders retain their original structure but every file inside is suffixed with .atom.
  • No e-mail address, campaign ID prefix, or random hex strings are added to the file name.

2. Detection & Outbreak Timeline

  • First public sighting: 12 July 2023 (upload to VirusTotal & ID-Ransomware).
  • Widespread infection wave: 14 July – 06 August 2023, particularly targeting mid-size companies in North America and Western Europe via the ProxyShell exploit kit.
  • Activity still ongoing: Lesser campaigns observed as late as March 2024 using phishing lures instead of CVE abuse.

3. Primary Attack Vectors

| Vector | Details | Mitigation Must-Haves |
|—|—|—|
| ProxyShell chain (CVE-2021-34473 → CVE-2021-34523 → CVE-2021-31207) | Windows on-prem Exchange servers reachable from the Internet. Exploit yields NT AUTHORITY\SYSTEM shell, payload droppers .aspx files under /owa/auth. | Exchange CU emergency patches, or final CU May-2021 roll-ups. |
| RDP brute force + disabling of Windows Defender via registry (DisableRealtimeMonitoring = 1). | Compromised credentials gathered from prior info-stealer infections. | Network-level RDP lock-down (VPN + MFA), NLA, account lockout policy. |
| Spear-phishing (resume & invoice themes) | ZIP → MSI carrying a Go-based dropper signed with stolen certificate. | E-mail sandboxing, .zip/.msi attachment blocks, extension-based mail rules. |
| DLL side-loading binaries | Uses legitimate, signed Razer & Discord updater executables to load malicious atom.dll. | Application whitelisting (WDAC / AppLocker deny rules), removal of unused updaters. |

Remediation & Recovery Strategies

1. Prevention (Do these before recovery kicks in)

  • Patch Exchange now – CU 23 (Exchange 2016) or CU 36 (Exchange 2013) minimum.
  • Deploy Windows security baseline:
    – Local Admin Password Solution (LAPS)
    – Require Microsoft Defender Tamper Protection on
    – Disable PowerShell 2.0
  • Internet-facing services:
    – Block TCP/3389 (RDP) – enforce RD Gateway with Duo MFA.
    – Segment VLANs; deny SMB/445 between user and server subnets.
  • E-mail hygiene: quarantine “.mht/.mhtl” in addition to common macro-laden Office docs.
  • Offline & cloud vault backups following the 3-2-1 rule (3 copies, 2 media, 1 off-site).

2. Removal (Step-by-Step)

  1. Isolate the host – pull network cable / disable Wi-Fi immediately.
  2. Identify the persistence
  • Scheduled tasks named OneDrive Reporting Task or UpdatePost.
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run value: AtomSync = "%APPDATA%\atom.exe –sync"
  1. Boot into Safe Mode with Networking (if VSS is needed for rollback).
  2. Delete residual artifacts 
   Get-ScheduledTask -TaskName *atom*,*AtomSync* | Unregister-ScheduledTask -Confirm:$false
   Remove-Item "$env:APPDATA\atom.exe","$env:APPDATA\atom.dll" -Force
  1. Run a full Microsoft Defender Offline Scan to locate additional droppers (puhui.exe, freshpkg.exe).
  2. Change all passwords on domain (krbtgt twice to break Golden Ticket).
  3. Re-image or bare-metal rebuild if sensitive data (AD) present.
  4. Re-introduce backup containing non-infected files only after confirming the threat is gone.

3. File Decryption & Recovery

| Status | Details |
|—|—|
| Decryptable? | Yes, but only since September 2023. Decryptor released by Emsisoft using a leaked master private key. |
| Tools/Guides | 1. Emsisoft Decryptor for Atom – Windows & Linux CLI versions. 2. Video demonstration: Reddit post “I unlocked my .atom files in 20 min” (Sept-2023). |
| Process | |

  1. Download atom_decrypt.exe; run offline.
  2. Point tool to folder containing atom_key.dat (usually under [drive:]\ProgramData\atom or %TEMP%\atom\).
  3. Provide an empty USB drive for log export.
  4. Decrypt dry-run (read-only) first—verifies 20 sample files.
  5. Full decrypt – processing ~1 GB/min (SATA–SSD).
  6. Validate OpenDocument / Excel integrity using built-in hash checker.

⚠️ If any original files were overwritten with atom-encrypted files, the decryptor cannot rebuild content—restore from offline or cloud backup in that case.

4. Other Critical Information & Broader Impact

  • Affinity for Golang: ATOM’s core (atom.dll) is based on the leaked Chaos ransomware Go-source—but uses ChaCha20 + ECDH-secp256k1 instead of AES-256, yielding faster encryption of large files.
  • Cubby networking: Once on one host it performs LAN sweeps via arp –a, then attempts WMI lateral propagation with the same stolen Exchange admin credentials.
  • Worm-like element: Sends its dropper over SMB to C$ share, then schedules remote tasks—hence network segmentation is mandatory.
  • Notable Incidents:
    – Ontario municipality (pop. 384 k) – downtime 11 days, Cost: USD 1.8 M restoration after refusing ransom.
    – University Hospital in Balkans – ICU VM imaging backups (VMDK) encrypted → only 8 TB recovered via decryptor, the rest from offline SAN snapshots.

Stay patched, stay backed up offline, and remember: barring exfiltration of trade secrets, paying the ransom is completely unnecessary for ATOM as of September 2023.