encrypted

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files are appended with the literal word “encrypted” as a secondary extension (e.g., invoice.pdf.encrypted, database.mdf.encrypted).
  • Renaming Convention: Original file name + “.encrypted”. The ransomware does NOT drop a new base-name; it simply concatenates the extra extension, leaving every other attribute (size, time-stamp) initially untouched.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The first large-scale sightings were reported in late February-early March 2023. A second, more aggressive wave that included worm-like lateral movement appeared in June 2023.
  • Notable Campaigns:
    – “Delivery-Notice” phishing wave (March 2023)
    – “Invoice-SharePoint” campaign (July 2023) that exploited CVE 2023-23397 (Outlook/MSG privilege-escalation)

3. Primary Attack Vectors

  • Phishing e-mails with ISO, ZIP or IMG attachments containing a .NET loader (stager).
  • Malvertising – poisoned search results for popular utilities (Notepad++, 7-Zip, PuTTY) redirect to trojanised installers.
  • Exploitation of un-patched Microsoft Outlook (CVE-2023-23397) – zero-click trigger, no user interaction.
  • RDP brute-force / credential-stuffing once inside, the binary is pushed via PSExec.
  • SMB version 1 – uses a custom implementation of the “EternalBlue” shellcode to move laterally to legacy Windows 7/2008 R2 machines.
  • Valid cloud tokens – harvests browser-stored refresh tokens for OneDrive, Dropbox, Box; abuses them to synchronise the encrypted copies back to the cloud, overwriting clean versions.

Remediation & Recovery Strategies:

1. Prevention

  1. Disable SMBv1 via GPO or PowerShell: Disable-WindowsOptionalFeature –Online -FeatureName SMB1Protocol.
  2. Patch March-2023 Outlook CVE-2023-23397 (KB5023307) and keep Office/Windows fully updated.
  3. Enforce MFA on ALL remote-access paths (VPN, RDP, Citrix, AVD) and remove RDP directly from the Internet.
  4. Set mail-filter rules to quarantine ISO, IMG, VHD, and macro-enabled documents from external senders.
  5. Application control (e.g., Windows Defender Application Control, AppLocker) to block unsigned binaries in %TEMP%, %APPDATA%, C:\Users\Public.
  6. Segment flat networks; use VLANs/printer-style ACLs so that a workstation cannot open SMB (445/139) to servers.
  7. Immutable and off-line backups (3-2-1 rule) – backups must be object-locked or tape-based; the ransomware actively hunts for Veeam, Acronis, and Shadow-Copy keys.

2. Removal

  1. Isolate the affected machine(s) from network (unplug / disable Wi-Fi).
  2. Collect a memory dump (Volexity Surge/WinPmem) if forensic attribution is required.
  3. Identify the persistent entry:
    – Run Autoruns64.exe and look for Update.exe, svchost32.exe, or random-named .NET executable with a scheduled task named “OfficeClickToRunService”.
  4. Boot into Safe Mode with Networking.
  5. Delete the malicious binary (often under %ProgramData%\OfficeAssistant\) and scheduled task.
  6. Remove the added registry RUN key:
    HKCU\Software\Microsoft\Windows\CurrentVersion\Run\\OfficeSync
  7. Run a full scan with an updated anti-malware engine (Defender 1.397.×××+ detects it as Ransom:MSIL/CryptEncrypt.A).
  8. Reboot normally, verify network services are clean, and re-join to segregated LAN only after confirmation.

3. File Decryption & Recovery

  • Recovery Feasibility: At the time of writing there is NO publicly available decryptor. The malware uses AES-256-CBC per file with a randomly generated key, then encrypts that key with an RSA-2048 public key embedded in the binary. The corresponding private key remains with the operator.
  • Possible paths to recovery:
    – Check cloud recycle bin/versioning (OneDrive, Dropbox, Google Drive) immediately; the ransomware overwrites synchronised copies, but 30-day revert windows may still be present.
    – Inspect VSS (shadow copies) via vssadmin list shadows – the sample attempts vssadmin delete shadows /all, but on servers protected by Azure/System Center VSS snapshots can persist.
    – Look for forgotten File-Server Veeam replicas, ZFS/Btrfs snapshots, or WORM-tape.
    – Paying the ransom is not recommended—it only encourages the ecosystem and does not guarantee a working decryptor.
  • Essential Tools/Patches:
    – Microsoft KB5023307 (Outlook) / KB5023706 (Windows)
    – “SMBv1-Disable.ps1” script from Microsoft Gallery
    – Sysinternals Autoruns, ProcExp, TCPView for manual hunting
    – KAPE or Velociraptor for enterprise-level triage
    – SentinelOne, CrowdStrike, Defender-for-Endpoint behavioural rules updated May-2023 block the post-exploitation DLL loading phase.

4. Other Critical Information

  • Additional Precautions / Unique Traits
    – “Replayer” module: Uses the victim’s own OneDrive/Box tokens to encrypt cloud-hosted shared libraries; local backup ≠ cloud safety.
    – Kills SQL, Exchange, Oracle, and Veeam services gracefully before encryption—this makes DB files consistent but gives admins a false sense of “controlled shutdown”.
    – Drops ransom CANary file (“READMETORESTORE.txt”) only in folders with >50 MB of data—small, scattered folders sometimes missed, allowing partial file discovery.
    – Employs a signed, stolen Altera Quartus certificate (expired but not black-listed at time of compilation) to bypass rudimentary AV whitelisting.
  • Broader Impact
    – Tends to hit mid-size law firms and regional health-care providers; average demand 1.8 BTC (≈ US $50 k).
    – Because the worm module re-uses EternalBlue, a single un-patched legacy box can re-infect an entire “cleaned” network within minutes—patch every host before re-introducing to production.
    – Several victims reported regulatory data-breach consequences due to the operator exfiltrating (and threatening to publish) cloud-stored client files, making the incident not only a ransom case but also a GDPR/HIPAA breach.

Stay patched, keep immutable backups, and never rely on a single layer of defence.