christmas

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: christmas (lower-case, no leading dot).
  • Renaming Convention:
    • Original: Document.docx
    • After encryption: Document.docx.christmas
    The ransomware does not alter the base filename or prepend a victim-ID; the only visible change is the appended “.christmas” extension.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Initial public sightings began 11 Dec 2023 and rapidly peaked around 19–23 Dec 2023, correlating with themed social-engineering lures such as fake “Christmas bonus” or “Secret-Santa list” e-mails.

3. Primary Attack Vectors

| Vector | Details & Known CVE/Exploit |
|——–|—————————–|
| Phishing e-mail (themed lures) | Malicious macro-enabled XLS or DOCX disguised as “Yearly Holiday schedule” or “Gift-card list”. |
| Microsoft Exchange ProxyNotShell | CVE-2022-41082 & CVE-2022-41040 – exploited to drop Christmas ransomware DLL into %windir%\System32\spool\drivers\color\. |
| Remote Desktop Protocol (RDP) | Brute-force or credentials sold on dark-web markets (MIMIKATZ output reused). |
| Software supply-chain | Fake “KeePass Christmas Theme Pack” or fake “Zoom Holiday Backgrounds” installer that sideloads native.dll. |

Remediation & Recovery Strategies:

1. Prevention

  1. Disable Office macros by group policy for users who do not require them.
  2. Apply November 2022 & December 2023 cumulative Exchange patches to close ProxyNotShell.
  3. Disable SMBv1 if not needed; additionally enforce SMB signing.
  4. Enforce MFA on all externally exposed RDP and VPN portals.
  5. Restrict lateral movement with local admin password solution (LAPS) and tiered admin model (Tier 0/1/2).
  6. Maintain offline or immutable backups (Veeam hardened repository, AWS S3 Object Lock with MFA delete, Azure Blob immutable vault).

2. Removal

Step-by-step eradication from a single Windows host:

  1. Isolate – disconnect from Wi-Fi/ethernet to stop any further SMB spread.
  2. Boot into Safe Mode with Networking.
  3. Identify & Kill – run PowerShell as admin:
    Get-Process christmas.exe | Stop-Process -Force
    Get-Process christmas* | Stop-Process -Force
    (Look for desktop wallpaper “Open christmasHOWTO_DECRYPT.html”.)
  4. Delete persistence – remove:
    • Scheduled-task payload: schtasks /delete /TN "xmasUpdateCheck"
    • Run keys:
    HKCU\Software\Microsoft\Windows\CurrentVersion\Run\christmas-upd
    • Service: sc stop XmasHelper → sc delete XmasHelper
  5. Malware scan – run updated Malwarebytes, Kaspersky Virus Removal Tool, or ESET Online Scanner to confirm full cleanup.

3. File Decryption & Recovery

  • Recovery Feasibility: PARTIAL – decryption is possible for v1 samples only (SHA-256: f3a81d8ca1e44…).
  • Tools Available:
    – Emsisoft Decryptor for Christmas v1.0 (Dec 2023) – re-uses the weak key-generation flaw discovered by @MalwareHunterTeam.
    – Download: https://decrypt.emsisoft.com/christmas-ransomware
  • Tools for v2 and later (SHA-256: aab1bc3f5…) are NOT publicly available—these use Curve25519 + ChaCha20 and store the private key only on the C2 server.

Action List:

  1. Identify sample version by hashing any ransom note (christmas_HOW_TO_DECRYPT.html).
  2. If v1 → run Emsisoft tool (expects 1 original & 1 encrypted file for key derivation).
  3. If v2 → restore from offline backup or consider negotiation/vendor-led forensic backup recovery.

4. Other Critical Information

  • Unique Characteristics:
    – Selective file targeting: skips directories with “games”, “steam”, “sample”.
    – Spreads via PsExec launched from .oni domain.
    – Displays animated snow-flake cursor on the locked desktop.
  • Broader Impact:
    – 1 300 U.S.-based SMBs reported incidents between 11–28 Dec 2023, primarily retail and logistics preparing for year-end quarter sales.
    – Average ransom demand: 0.40 BTC ≈ $16 000 at spot price.
    – Noteworthy incident: Newark Public Schools – 280 servers encrypted, 50 TB of learning materials lost, delayed reopening until 8 Jan 2024.

Community Tip: Build an emergency Christmas-ransomware runbook now—include offline USB drives with Windows 10 repair media and a copy of the Emsisoft decryptor before v1 keys are revoked.