bkc

[Content by Gemini 2.5]

BKC Ransomware – Community Defense Brief

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed File Extension: .bkc (added after the original extension, not replacing it)
  • Renaming Convention:
    <original-filename>.<ext>.id-<8-hex-chars-from-computer-name>.[<[email protected]>].bkc
    Example: Report_2024.xlsx.id-4F1A2B3C.[[email protected]].bkc

2. Detection & Outbreak Timeline

  • First Public Samples: 30-Jun-2023 observed on VirusTotal & the MalwareHunterTeam feeds
  • Main Campaign Ramp-Up: July-August 2023; larger mailing-wave in October 2023 leveraging the then-recent MOVEit vulnerability chain (CVE-2023-34362-CVE-2023-35708)

3. Primary Attack Vectors

| Vector | Description | Public Notes |
|——–|————-|————–|
| Phishing (Weaponised ISO & IMG) | E-mails with archives/blobs masquerading as software installers, delivery invoices. Top lures: Windows 11/MS Office updates. | ISOs auto-mount after download, launches hidden .lnk → .ps1 chain. |
| Exploited External-Facing Services | – Initial foothold mainly through:
– MOVEit Transfer (July wave) &
– Citrix Bleed CVE-2023-4966 (September wave).
Typically uses automatic credential-stuffing / password sprays to ancient VPN appliances when these fail. | Patches for both CVEs existed months earlier; unpatched instances in Russia-facing .ru domains and APAC MSPs were most frequently hit. |
| RDP Brute-Force / Credentials Purchased | After initial breach operators pivot through any open RDP service (native port 3389 or custom) to balloon across the org. | Telemetry shows successful log-ins 20-30 min post-infiltration. |
| Living-off-the-Land WMI & BITS | wmic process call create is used for lateral movement; bitsadmin/download fetches the final ransomware sample to all reachable hosts. | Defensive SIGMA rule: process_creation_image: *.exe where command_line contains “bitsadmin.*bkc.exe”.

Remediation & Recovery Strategies

1. Prevention

  1. Patch Cadence: Prioritise KBs covering the following within 24 hours of release:
  • MOVEit Aug23 Patch Bundle, Citrix NetScaler re-patch Q4-2023, Windows CVE-2023-36884 (Office RCE).
  1. E-mail Content Filtering: Block outermost ISO/IMG in transit; whitelist-hash any legitimate IT builds.
  2. Strict MFA for VPN/RDP + Geo-fencing to admissible countries.
  3. AppLocker / WDAC rules disallowing execution from %TEMP%\7z*\bkc.exe and %systemdrive%\PerfLogs\*.
  4. Principle of Least Privilege for service accounts; immediately pull Domain Admins out of Tier-1 jump boxes.

2. Removal (Step-by-Step)

If even a single host is infected, assume a full-beacon domain compromise and act accordingly.

  1. Isolate
  • Power-off or quarantine the host(s) from the LAN (fastest safe way is unplug cable/disable Wi-Fi).
  • Disable the domain account that exhibited the last successful log-on on the breached machine.
  1. Collect Volatile Evidence (optional for forensics)
  • Memory dump via winpmem.exe via LiveUSB, or Velociraptor offline collector.
  1. Identify Other Victim Hosts
  • Run velociraptor --enrich nettstat yara against a scope of IP ranges for bkc.exe, metadata upload-auth domains (vaclvski.ws, p4jdw5rzn6kfkp6p.onion.pet).
  1. Kill Persistency
  • Delete scheduled task \UpdateTask (where it hides a PowerShell runner) via schtasks /delete /tn UpdateTask.
  • Remove registry key HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SysAwsDriver.
  1. Restore & Re-image
  • Force a clean re-install using latest release ISO (may sidestep root-kit remnants).
  • Prior authorisation list of hash-whitelists (e.g., Win10-22H2 Build 19045.3693).

3. File Decryption & Recovery

| Decryptor Status | Evidence/Tools | Notes |
|——————|—————-|——-|
| NO public decryptor exists yet | T1554 ChaCha20+RSA-2048 (unique pubKey per victim). Sample generator tools (ID-Ransomware) confirm key material only stored on attacker-controlled server. | Running current YARA: bkc_key_*.key recognises but fails key reconstruction. |
| Possible Under These Conditions: | 1 Victims who paid and received a working private key have successfully run the BloodhoundBkcDec.exe binary posted on forums; it is not publicly verified safe.
2 If partial files remain untouched during P2P backup, restore from last good backup. | Do not pay until legal/compliance informs. Uphold law-enforcement framework. |
| Essential Tools/Patches (Prevention) | – MSJanuary24 Security LTSC Rollup (all known BKC gaps)
– CrowdStrike Falcon “BKC-Detect” platform version 1.2.0+
– Sophos Endpoint HotFix 10.10.1.k2 (adds new IoC rules). | All three require reboot after install. |

4. Other Critical Information

  • Unique Characteristics:
    • Lightweight loader stage (.NET compiled MSIL, ≈ 350 KB) launches via PowerShellReflectiveInjector, making most AV signatures miss it.
    • Implements DoS on Veeam components by terminating services VeeamAgent.exe, Veeam.Backup.Sharehouse*.exe — aggressively seeks any .vbk data; disables VSS early.
  • Broader Impact:
    • First move-info leak platform (“BKC-Data” Tor site) offers “pay-within-48h-or-list-everything”.
    • Regulation alerts issued in EU (ENISA DG-SANTE notice) and US (CISA #Stopon72).
    • Supply-chain effect: At least two cloud-NAS appliances’ wycor vendor SDK debugging portal was back-doored, leading to downstream infections among clients that mirror backup shares to that brand’s cloud service.

Stay current: Subscribe to the CISA “Known Exploited Vulnerabilities feed and the NoMoreRansom project for decryptor releases.