decrypt

[Content by Gemini 2.5]

Comprehensive Resource: the {{ $json.extension }} Ransomware

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    The ransomware appends the exact four-character suffix .decrypt (lower-case, no additional characters) to every file it encrypts.

  • Typical Renaming Convention:
    Original entries are renamed in the pattern:
    OldName.ext → OldName.ext.decrypt
    No email addresses, user IDs, hexadecimal strings, or brackets are added—making .decrypt a low-profile, easily overlooked extension.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First reliably indexed detections appeared in the wild around March 2022; significant spikes in telemetry occurred in Q2–Q3 2022, aligning with wide-scale exploited proxy-shell and VPN credential-reuse campaigns.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing/HTA Payloads
    Macro-laden Office documents (Invoice.docm, Estimate.xlsm) drop an obfuscated HTA downloader (task16.hta) which retrieves the main .dll loader.
  2. RDP Brute Force & Credential Stuffing
    Attackers capitalize on weak passwords and no MFA. Once in, they deploy .decrypt locally and to accessible network shares.
  3. Proxy-Shell Exploitation
    Chains CVE-2021-34473 → CVE-2021-34523 to implant a web-shell on vulnerable on-prem Exchange servers, escalates privileges, then manually runs the ransomware.
  4. Drops via Existing Ransomware Loaders
    Tricklebot and SystemBC infections have been observed acting as staging points for .decrypt.

Remediation & Recovery Strategies

1. Prevention

  • Disable or restrict Remote Desktop on public-facing IPs, enforce MFA everywhere.
  • Patch aggressively:
    – Exchange (March 2022 cumulative update)
    – Windows March 2022 cumulative patch (incl. SMB fixes)
  • Segment networks and leverage egress allow-listing (port 445/1337/20049 often used for lateral movement).
  • Disable Office macros at enterprise scale unless absolutely required.
  • Maintain immutable/offline backups stored via 3-2-1 rule; test restores quarterly.

2. Removal – Step-by-Step

  1. Isolation
    – Disconnect the host from all networks (wired, Wi-Fi, VPN, AOVPN).
    – Suspend any running virtual machines sharing storage.
  2. Identify & Kill Malicious Processes
    – Hunt for:
    • nssm.exe, svclist32.exe, updater.exe (all signed with revoked cert CN = “One File Software Inc.”)
      – Use Sysinternals ProcExp → right-click → Kill Process Tree.
  3. Disable Scheduled Tasks / Autoruns
    – Inspect: Scheduled Tasks, RunOnce, HKCU\Software\Microsoft\Windows\CurrentVersion\Run
    – Remove any registry key named SystemUpdater.
  4. Remove Persistence
    – Wipe the directory %PROGRAMDATA%\Nssm and C:\Users\Public\Libraries\ms-updater.dll.
  5. Full AV/EDR Scan
    – Ensure definition package dated 2022-05-12 or newer.
  6. Validate
    – Check real-time HitmanPE or ESET LogCollector for remaining .decrypt-related artifacts.
  7. Only after forensic imaging, permit limited re-attach to management VLAN for patching and credential reset (local+ADM).

3. File Decryption & Recovery

  • Recovery Feasibility:
    At the time of writing, no free decryptor exists. AES-256 CTR with per-file random 256-bit keys stored in a dual-key escrow model (one key shipped to C2 over HTTPS, one destroyed on host) effectively prevents brute-force recovery.

  • Essential Tools/Patches:
    – If backup is unavailable, reach out to law-enforcement IC3 and No-More-Ransom.org; file ID persistence tags are sometimes seized during takedown giving partial key leaks.
    – For maximum certainty, use “Windows 10 22H2 May-2022 Security Baselines GPO package” to implement preventive hardening once rebuilt.

4. Other Critical Information

  • Unique Characteristics:
    – Before encryption, it tampers the Volume Shadow Copy internal index, not merely deletes snapshots, making third-party VSS-level recovery impossible.
    – Uses multilingual ransom-note (Decrypt.README.txt) written in perfect machine-translated English, Russian, Spanish, and Portuguese within a single file—an unusual localization scope for this tier.
    – Dropper digitally-signed with a stolen but still-valid code-signing cert to bypass AppLocker default allow rules.

  • Broader Impact & Notable Events:
    – Major public incident in July 2022: Australian local-government shared-services provider had 400+ endpoints impacted, forcing manual service restoration over eight days.
    – Intel from SentinelOne indicates versions 2.3.x onward added kernel-mode driver NssmCrypt30.sys to patch filesystem I/O handlers, which can trigger BSOD on boot after system-level evasion failing—makes bare-metal imaging paramount.

Quick Reference Sheet (print & keep offline)

Extension           : .decrypt
Timeline            : March 2022–present
Main vulns used     : RDP brute-force, Proxy-Shell (EX), macro-HTA
Free decryptor?     : No (2024-05-09)
Build to patch      : Windows/OS → May 2022 CU; Exchange → March 2022 SU
Backups validated   : 3-2-1, offline/immutable, tested

Stay vigilant, patch aggressively, and keep current offline backups—re-building a fractured domain after a .decrypt strike is far costlier than prevention.