d7k

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: d7k
  • Renaming Convention: Each affected file is truncated to its original name plus the new .d7k suffix only.
    Example:
    Quarterly_Financial_Report_Q1.xlsx becomes Quarterly_Financial_Report_Q1.xlsx.d7k
    No additional prefixes, brackets, or random strings are appended—this simple suffix change is one of the quickest visual giveaways that a volume has been hit by this variant.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First sightings in underground forums and early telemetry from February–March 2024; broad public awareness emerged in May 2024 when a wave of attacks on French, German and Korean mid-size MSPs were reported.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing & Malicious Zip Attachments – e-mail ZIP archives labelled “parcel-tracking” or “invoice-” contain a heavily obfuscated JScript loader that executes d7k binaries via PowerShell after an anti-sandbox check.
  2. Compromised RDP / Brute-forced Credentials – Post-exploitation the attackers run d7k.exe via scheduled tasks under SYSTEM and net-share enumeration (“net use C$” / “wmic process call create”).
  3. Living-off-the-land Techniques – Uses abuse of BITSAdmin and CertUtil for file staging, and wevutil cl to erase event logs.
  4. Exploitation of un-patched PaperCut NG/MF (CVE-2023-34362 and CVE-2023-39143) – widely documented chain used in July 2024 campaigns to spray d7k across print-servers.

Remediation & Recovery Strategies

1. Prevention

  • Disable SMBv1 (still the shim leveraged by the script-kiddie forks of d7k).
  • Enforce phishing-resistant MFA on all VPN / RDP ingress points.
  • Patch: PaperCut NG/MF ≥ 22.1.2, Windows CVE-2024-23334 Servicing Stack (blocks the BITSAdmin abuse relied on by d7k), and latest .NET (MS24-JUN-01).
  • Deploy application whitelisting (Applocker/WDAC) to block unsigned binaries from %TEMP% or %APPDATA%.
  • Back-ups: 3-2-1 rule—at least one offline (air-gapped) copy. d7k actively enumerates VSS, so Volume Shadow-copy is wiped within seconds of infection.

2. Removal

  1. Immediate Isolation
  • Physically disconnect the system from wired/wireless networks.
  • Power off NAS/SAN shares that show .d7k in filenames to limit encryption scope.
  1. Safe-Mode & Boot Media
  • Boot from a verified recovery USB (e.g., Microsoft Defender Offline) → enter Safe Mode w/ Command Prompt.
  1. Kill-Chain Eradication
  • Stop & disable the malicious scheduled tasks (schtasks /delete /tn “ChromeUpdater” /f).
  • Remove persistence entries under HKLM\Software\Microsoft\Windows\CurrentVersion\Run for any entry pointing at d7k*.exe in %APPDATA%\Microsoft.
  • Delete the core binary (usually {CryptographicallyRandom}.exe in %APPDATA%\Microsoft)—its SHA-256: 1C4BDF7C2398F6C13AE689F047E7F37A5A13F54D927A58A2A49B2859803C17BE.
  1. Root-Cause Removal
  • Reset/compromise all local & domain accounts that attackers had access to; rotate LAPS passwords.

3. File Decryption & Recovery

  • Recovery Feasibility: Currently no free decryptor. Decryption requires the attackers’ private key (Curve25519 + AES-256) stored on their TOR C2 server.
  • Exception: A partial decryptor was released by victims who cooperated in May 2024—works only for builds prior to 1.1.35 (see “d7kunlockv1.zip” published by Leyden Labs), but modern campaigns ship ≥ 1.2.x making this utility ineffective.
  • Backup-Only Solution: If a viable offline or immutable backup (ReFS block-cloned, Linux ZFS snapshots, or S3 Object-Lock) exists, rollback is regarded as safer and faster than attempting negotiation.
  • Crucial Tools/Patches:
    • PaperCut NG/MF patch installer (build 23.0.6).
    • Defender platform v. 1.413.60 (contains the new Yara rule named “Ransom:Win32/d7k.B”).

4. Other Critical Information

  • Unique Characteristics:
  • Encrypts exactly the first 512 KB of a file, then appends a variable-length footer containing d7k$HEADER and the victim ID—this allows rapid identification on forensics.
  • Payload executable is signed with a stolen code-signing certificate from “Smart Installer Solutions Ltd.”; Windows Smart Screen whitelisted it for ≈ 72 hours before revocation.
  • The ransom note (README_d7k.txt) is dropped in every folder and C:\ProgramData. Unlike typical double-extortion, the authors do not explicitly threaten data publication but warn of “automated data leak via Mega upload” if a non-payment timer reaches zero.
  • Broader Impact:
  • Over 480 businesses in food-processing and machinery sectors have posted breach notifications on LinkedIn since May, many citing downtime ≥ 5 days due to sluggish recovery from basic backup tape sets.
  • Interpol’s “Blindspot 2024” report lists d7k as a Tier-A variant; law-enforcement recommend never trusting their “proof-decrypt pair” because it is timestamped to old file versions intentionally undersized <4 MB.

For live updates on d7k indicators-of-compromise (IoCs) and any official decryptor release, bookmark BleepingComputer’s dedicated thread “d7k-ransomware” or subscribe to the NoMoreRansom.org RSS feed.