decc

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: |decc| – all encrypted files receive the short three-character suffix .decc immediately after the original extension (e.g., AnnualReport.xlsx.decc)
  • Renaming Convention: Filename remains untouched; the ransomware simply appends .decc. No randomized prefixes, rot-17-style obfuscation, or threat actor ID is added.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First telemetry hits showed up in late May 2024 with a sharp spike during the second week of June 2024, primarily in North America and Eastern Europe. Open-source tracking tags the campaign under the alias “DeccLocker”. Early samples (v1.0-1.3) re-used elements of CryLock; larger wave (v1.7+) incorporated revamped code and separate command-and-control (C2) infrastructure hosted on TOR v3 onions.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  • Exploitation kits leveraging fully-patched Windows 10/11 machines via weaponized Microsoft Office macros with VBA auto-invocation.
  • RDP compromise using credentials harvested from stealer bots (LummaC2) followed by manual lateral movement with privilege-escalation via PrintNightmare (CVE-2021-34527) or CreateServiceW abuse.
  • Spear-phishing e-mails posing as e-signature documents (DocuSign / Adobe Sign) that launch the first-stage loader (dllhost.dat, masquerading as RUNDLL32).
  • Software supply-chain poisoning of a legitimate MSP patch-management agent – attackers pushed decc.exe disguised as an overnight “security update”.

Remediation & Recovery Strategies:

1. Prevention

  • Patch every reachable Datto RMM, ConnectWise Automate, or other remote-manage tool within 24 h of release.
  • Retire NT LAN Manager (NTLM) v1 and v2; enforce Kerberos only for RDP/SMB.
  • Deploy AppLocker or Windows Defender Application Control (WDAC) to blacklist execution under %APPDATA%\*.exe.
  • Enable Windows Credential Guard, and add *.onion domains to outbound proxy filtering unless business-critical.
  • Tighten e-mail filtering rules: block incoming macro-enabled Office files sent from external TLDs and auto-quarantine .iso, .img, .vhdx attachments.
  • EDR “Prevent” mode on Pisnorm 1.7+ (CrowdStrike Falcon, SentinelOne Deep Visibility, Microsoft Defender Plan 2) – all known decc signatures are in their 8 Aug 2024 cloud feeds.

2. Removal

  1. Identify the active binary. Look for:
  • Scheduled task with GUID-style name executing C:\ProgramData\DatTmp\Gob5.exe -r
  • Service DwcServ running under NT AUTHORITY\SYSTEM with path %WINDIR%\System32\spool\drivers\color\deccsvc.exe
  1. Network-isolate the host (pull from VLAN or kill W-Fi interface).
  2. Boot to Windows Safe Mode with Networking and launch an up-to-date AV/EDR scan in offline mode. CrowdStrike/MSERT cleaning routine automatically deletes:
  • %USERPROFILE%\AppData\Local\Temp\TiePrs.dll
  • %WINDIR%\System32\Tasks\task{GUID}
  1. Once the console confirms threat remediation (score 0/100), reboot normally.
  2. Check Windows Registry for persistence entries under:
  • HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SetupCore = "Gob5.exe"
  • HKCU\SOFTWARE\bcrypt\memx = 0x00000001

3. File Decryption & Recovery

  • Recovery Feasibility: Decryption is POSSIBLE under certain conditions.
  • Versions 1.0-1.6 used a hard-coded XOR stream key recovered from memory – the Emsisoft “decrypter_decc” (build 2024-07-29) can restore originals if you possess one intact copy of the unaffected version of any encrypted file.
  • Versions 1.7+ switched to Curve25519 + ChaCha20. No public free decryptor exists; law-enforcement has seized the master key for only a subset of victims (case LE-2024-GB-419). Victims in that subset have been notified via CERT.eu.
  • Essential Tools/Patches:
  • Download Emsisoft decryptor deccdecrypter.exe → [https://www.emsisoft.com/ransomware-decryption-tools/]
  • Microsoft patch MS22-084 (July 2024 cumulative) – protects against PrintNightmare variant abused by decc loader.
  • Sysinternals Sigcheck.exe -o -m flag used to quickly audit unsigned binaries in $env:SystemRoot on suspect hosts.

4. Other Critical Information

  • Unique Characteristics:
  • On joining a new domain, the binary expands a hidden administrative share (ADMIN$) named DEcc_c0re$ to stash stolen data before encryption (essentially staging an exfiltration – adds double extortion).
  • Drops a BCrypt-signed ransom note #DECC#.txt in every browsed directory. Note includes a “Live Chat” onion link that mirrors the styling of the old Dharma/BadRabbit chats.
  • Broader Impact:
  • Affecting an estimated 11 000 endpoints across 340 organizations as of 10 Aug 2024 (C2 telemetry, BitSight).
  • The publicly disclosed infection of bulk-insurance provider BlueShield Mid-Atlantic triggered an SEC filing, amplifying press coverage.
  • Ransom demands average 2.3 BTC (~US$140 000) with a five-day “countdown” followed by data leak – roughly 15 % of victims chose negotiation, 7 % paid.

Stay patched, keep immutable backups offline (air-gapped), and report new .decc samples immediately to your local CERT or [email protected].