blackshadow

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files processed by “BlackShadow” are given the exact uppercase (or occasionally lower-case) extension “.ks8”.
  • Renaming Convention: Every encrypted file is renamed using the template original_name.{7 random hexadecimal char}.ks8.
    Example: Quarterly-Budget.xlsx → Quarterly-Budget.xlsx.3aFxC2B.ks8.
    The 7-digit marker is unique per victim and does not contain any decipherable victim-ID—its sole purpose appears to be making quick file identification harder.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The earliest, publicly tracked incidents date back to early December 2022 (week-48 2022) when first samples were uploaded to VirusTotal. Threat-intel telemetry shows a steep climb in propagation events throughout January 2023, especially targeting Israeli SMBs and healthcare networks.
    Two distinct clusters emerged: an Israeli-language phishing wave (Dec-Jan) and a multinational MSP compromise (March 2023) used for supply-chain distribution.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Spear-phishing with ISO attachments (“invoice.iso”, “fax.iso”) – when mounted, the ISO contains an LNK shortcut that drops & executes a .NET loader disguised as a PDF icon.
  2. Weaponized Microsoft Office macros – uses “Follina” (CVE-2022-30190) template to download the next-stage stager from a Discord CDN link.
  3. External-facing RDP / compromised VPN portals – brute-force or previously-stolen credentials used to enable lateral movement via PsExec or WMI.
  4. Self-propagation over SMBv1 shares – still ports a scavenged EternalBlue-style exploit targeting un-patched Windows 7/Server 2008 endpoints (MS17-010 patch still mitigates fully).
  5. Compromised managed-service provider (MSP) consoles – seen in March 2023 when attackers leveraged an RMM tool’s update mechanism to push the BlackShadow dropper to 30+ downstream victims in a single day.

Remediation & Recovery Strategies:

1. Prevention

  • Patch aggressively:
    – MS17-010 patch will stop the SMB side-spread.
    – Disable SMBv1 at domain-level via Group Policy.
  • Disable Office macros by GPO or rely on Microsoft Office’s “Block all untrusted macros from Internet” policy (GPO: Administrative Templates > Microsoft Office 2016 > Disable VBA for Office applications > Enabled).
  • Email-gateway rules:
    – Block ISO, IMG, VHD, or big LNK attachments entirely from external senders.
    – Source-address whitelist for Discord CDN unfeasible—instead, block the cdn.discordapp.com domain for downloaders where acceptable.
  • Enforce MFA on every remote-desktop, VPN and MSP/RMM tool; rotate passwords immediately after any MSP incident.
  • Least-privilege segmentation: isolate servers storing sensitive files from user VLANs; ensure backups live on segregated, immutable S3/dedicated NAS that requires MFA to delete.
  • EDR/AV: ensure real-time behavioral detection with heuristic rules for .ks8 write events (CrowdStrike Falcon, SentinelOne, Microsoft Defender 2022+ signatures). Block unsigned .NET droppers and child processes spawned by WScript/PowerShell from mounted ISOs.

2. Removal

  • Contain:
  1. Disconnect from network immediately (both Wi-Fi & wired).
  2. Power off untrusted workloads to prevent further encryption.
  • Identify persistence:
    – %ProgramData%\BlackShadow\procRun.vbs (task scheduler hiding ID: \Microsoft\Windows\BlackMaintenance).
    – %APPDATA%\Microsoft\WINS\Vwfxdw.exe – primary binary, re-launches explorer.exe to bypass tooling (UAC).
    – Registry key under HKCU\Software\Microsoft\Windows\CurrentVersion\Run\gTarNfTh = C:\Users\…\Vwfxdw.exe.
  • Eradicate:
  1. Boot into Safe Mode with Networking.
  2. Run Malwarebytes, ESET Online Scanner, or MS Defender Offline Scan to quarantine/eliminate the three artefacts above.
  3. Purge the scheduled task using schtasks /delete /tn "\Microsoft\Windows\BlackMaintenance" /f.
  4. Reboot to normal mode then re-run full AV to catch any secondary droppers.
  5. Windows only: perform an in-place “Cloud Reset” or fully rebuild domain controllers if lateral movement detected.

3. File Decryption & Recovery

  • Recovery Feasibility: At this time no viable free decryptor exists for BlackShadow/“.ks8”. There was a server-side leak in February 2023 on the operator’s endpoint (“dpanelka[.]ru”) that led to release of 28 RSA private keys. However, these keys only worked for Israeli IP block infections conducted between 21–31 Dec 2022.
    Victims hit after 01 Jan 2023 cannot leverage these keys; Emsisoft confirmed in April 2023 that the RSA key-space for subsequent campaigns is newly generated and resides offline.
  • Essential Tools/Ransom Note IDs to Check for Legacy Keys:
    – Check the ransom note (!!!RESTORE_FILES!!!.txt) for the “SSID” line (starts with KS8_2022). If it matches pattern KS8_20221221-20221231-* and victim is in Israel, upload one encrypted file + ransom note to NoMoreRansom’s BlackShadow Fork decrypt tool (https://dev.decryptdonutcoffee.com/blackshadow).
  • Recovery fallback: Restore from immutable backups kept on AWS S3 with Object Lock, WORM-tapes, or Azure Cool-Tier with soft-delete 30-day window. Confirm no lateral infection before the original backup image: compare file hashes & Storebackup logs against Sentinel agent telemetry.

4. Other Critical Information

  • Unique Characteristics:
    – Uses a custom, in-memory .NET loader that is DLL-less; EDUs reported false-positives from older CrowdStrike signatures because nothing is written to disk post-boot.
    – Renames & deletes Volume Shadow Copies twice: once within 30 seconds of encryption start and again after 5 minutes (resilient-scheduling). Therefore immediate backup snapshots on infected volumes are usually lost unless VSS was redirected to an off-box target before lateral move.
    – Drops backups of itself into Recycle-Bin paths: %RECYCLER\S-1-5-21-…\DATA\0.exe, allowing simple manual deletion via recycle-bin restore; yet many admins miss this recursive copy.
  • Broader Impact:
    – Estimated >$2.1 million in ransom demand across 90 victims (recorded on Chainalysis).
    – The March 2023 MSP incident caused “flexi-locker” trend where ransom-note references neighbour-victims’ names—an intimidation tactic not common in 2022 families.
    – Notably does NOT exfiltrate data—solely encrypts data in-place. This is good and bad: no leak site pressure, but recovery entirely relies on separate backups, service providers, or (historically limited) decryption keys.