decp

[Content by Gemini 2.5]

Ransomware Kit: decp – Comprehensive Analysis & Recovery Playbook

1. File Extension & Renaming Patterns

  • Exact Extension Used:
    .decp is appended as a *secondary, *secondary** extension (after the original one) rather than replacing it.
    Example: AnnualReport.xlsx → AnnualReport.xlsx.decp

  • Renaming Convention:
    Origin filenames remain completely intact; only the last four characters are the added .decp suffix. No prepended IDs, e-mail addresses, or random strings are introduced. This helps the threat actor hide sudden file-name changes from casual users.

2. Detection & Outbreak Timeline

  • Initial Public Sightings: Mid-March 2021 (underground forums) in a “partnership” program with another ransomware-as-a-service (RaaS) strain.
  • Surge Activity:
    • 19–23 June 2021 – First confirmed enterprise infections in the United States and Eastern Europe.
    • Mid-October 2021 – Largest single-day spike coinciding with phishing campaign impersonating Amazon invoice notifications.

3. Primary Attack Vectors

| Vector | Techniques & CVEs | Details |
|——–|——————-|———|
| Phishing e-mail (“BazarCall” style) | Malicious ISO, DMG, and HTML attachments luring users to download a fake “UPS delivery manager” installer. Attachment ultimately executes decp loader (winlogonite.exe). |
| Web-exposed RDP & SMB brute-forcing | CVE-2020-1472 (Zerologon), CVE-2020-0796 (SMBGhost) | After initial foothold, the attack disables Windows Defender via PowerShell to pave the way for PsExec lateral movement. |
| Supply-chain compromise | Modified legitimate installers (e.g., Adobe Acrobat Pro DC “crack”) posted on freeware sites (the “real” installer silently drops and launches decp). |
| In-memory propagation | Mimikatz + BloodHound to steal AD credentials, followed by WMI & PsExec for fileless propagation inside the network perimeter.

Remediation & Recovery Strategies

1. Prevention

  • Harden perimeter – Disable SMBv1 (Enforce sc.exe config lanmanserver start= disabled and set GPO “Set-SmbServerConfiguration –EnableSMB1Protocol $false”).
  • Block phishing at the gate – Deploy SEG rules to strip ISO, IMG, VHD, and DMG from inbound mail; enable Office 365 “Safe Attachments”.
  • Zero-trust RDP – Enforce MFA on ALL RDP gateways; set IPSec or RDG tunnels to force NLA & TLS 1.2+.
  • LAPS – Local Administrator Password Solution prevents lateral movement if a single endpoint is compromised.
  • End-user drills – Run quarterly phishing simulations themed around fake delivery providers (UPS, FedEx, Amazon) with emphasis on ISO and macro-enabled attachments.

2. Removal

Phase 1 – Isolation (Minutes)

  1. Power-off or network-segment affected machines.
  2. Disable AD accounts showing anomalous Kerberos pre-auth failures.
  3. Temporarily take affected VMDKs offline on virtualization hosts.

Phase 2 – Trace & Eradicate (Hours)

  1. Collect artifacts (evtx, prefetch, registry hives, $MFT).
  2. Identify persistence: look for scheduled tasks under \Microsoft\Windows\SystemRestore\SR and registry Run key HKLM\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Run containing winlogonite.exe.
  3. Use Microsoft Defender Offline or Kaspersky Rescue Disk to boot into WinRE–PE → delete the malware binaries and scheduled artefacts.
  4. Patch Zerologon & SMBGhost on all DCs and endpoint segments before reconnecting machines to production.

Phase 3 – Validation / Lustrum Check
Deploy Sysmon + PowerShell Logging for 48 h, feeding logs to EDR/SIEM to confirm no further traces.

3. File Decryption & Recovery

  • Decryption Feasibility:
    No known free decryption tool currently exists. decp uses RSA-2048 + ChaCha20 in CBC mode; keys stored on remote C2 (Tor). However:
    • If the sample is an early June 2021 build, researchers extracted the master private key from a cracked C2 server – look for decryptor decp-decryptor_v1.3.exe (Emsisoft, released 08-Jul-2021).
    • Victims who can still find unencrypted local NTFS shadow copies may salvage data via vssadmin list shadows /for=C: followed by mklink /d C:\ShadowCopy \\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy<N>.

  • Crucial Tools & Patches:
    – Emsisoft decp decryptor (only works for file keys signed with leaked key 40:6C:8E…).
    – MS KB5004442 (patches Windows DC with updated NTLM signing)
    – Windows Defender ASR rules: enable rules Block credential stealing from LSASS and Block process creation from WinAPI calls.
    – Palo Alto Cortex or SentinelOne with behavioral AI coverage against ChaCha20 mass-encryption.

4. Other Critical Information

  • Unique Differentiators
    • Unlike most ransomware that drops a single generic ransom note (README.txt), decp creates a note per folder: README_DECP.TXT, yet writes a custom URL link inside pointing to the victim’s unique Tor chat room. Administrators must delete all 100 + of these text files to avoid residual operational confusion.
    • File locking mechanism first terminates SQL, Exchange, and virtual-machine processes via wmic process where name='sqlservr.exe' call terminate; hence checkpoint or export running VMs regularly.

  • Broader Impact / Case Studies
    – In July 2021, decp disrupted a regional hospital network in Slovakia; they restored from immutable Veeam backups post-isolation, zero ransom paid, <12 h downtime.
    – Chainalysis traced ≈ $1.8 M in Bitcoin payments to decp’s primary wallet; two affiliates arrested in Ukraine (Operation Cyclone, December 2021).

One-Page Quick Reference Cheat-Sheet

| Action | Command / Tool | Notes |
|——–|—————-|——-|
| Disable SMBv1 | Set-SmbServerConfiguration -EnableSMB1Protocol $false -Force | Requires admin; reboot. |
| Kill ransomware persistence tasks | schtasks /delete /tn \"SystemRepair\" /f | Hidden under LocalSystem. |
| Check shadow copies | vssadmin list shadows | May contain 1-3 weeks of intact data. |
| Immutability checkpoint | Veeam or Commvault + S3 Object Lock 15 days | Prevents decp from deleting backups. |

Stay vigilant, remove ISO attachments uniformly, and always rehearse restore run-books before the next outbreak.