blackcat

[Content by Gemini 2.5]

Ransomware Community Resource
Targeted Variant: BlackCat / ALPHV (Observed file extension: .blackcat)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension → .blackcat (sometimes simply .alphv or a campaign-specific 3–4 character suffix supplied via affiliate JSON config).
  • Renaming Convention → Original file names are not merely appended—they are randomized using 5–6 lowercase letters plus the chosen suffix (e.g.,
    2024_Q2_Budget.xlsx → mfzkeo.blackcat). Each encrypted file is additionally written with a 32-byte blob at the end which contains its unique ChaCha20 file key, encrypted by the attacker-supplied RSA public key.

2. Detection & Outbreak Timeline

  • First public disclosure: posted on Russian-language crimeware marketplace in November 2021.
  • First high-profile victim (US fuel distributor) reported mid-Dec 2021. Peak activity observed Q1–Q2 2022; still actively maintained as of Q4 2024 through affiliate model (Ransomware-as-a-Service).

3. Primary Attack Vectors

  • Initial broker intrusion: Credential stuffing / brute-force against public-facing RDP / SSH; purchase of stolen VPN credentials in Telegram or Genesis-like markets.
  • Living-off-the-land: Uses WMI, PowerShell, PsExec, then embeds rust-based payloads (blackcat.exe) that can run on Win, Linux and ESXi.
  • Lateral movement: Exploits EternalBlue (MS17-010), PrintNightmare, Log4Shell (CVE-2021-44228), PaperCut (CVE-2024-27325); pivoting via RDP or Impacket secretsdump.
  • Defensive evasion: Disables Defender via AMSI bypass and deletes Volume Shadow Copies (vssadmin delete shadows /all /quiet).

Remediation & Recovery Strategies

1. Prevention Essentials

  1. Disable SMBv1 on every domain controller and endpoint.
  2. Apply every critical patch (especially Log4j ≥2.17.1, PrintNightmare, PaperCut, MS17-010).
  3. Harden perimeter services: Block internet exposure of RDP (port 3389/tcp) and SSH; enforce MFA on every VPN concentrator.
  4. Credential hygiene: Rolling forced-reset of local admin and service accounts; enforce 14-character minimum, NTLM hardening (LSA Protection, Defender Credential Guard).
  5. Tiered network segmentation with deny-all outbound firewall rules for high-value servers.
  6. Backups: 3-2-1 rule, air-gapped or immutable (e.g., Azure Blob With immutability, Veeam Hardened Repo). Test restores monthly.
  7. EDR + Microsoft Sentinel / CrowdStrike with detect-ions tuned to Rust Screenshot tool screenshotter.exe, bcdedit.exe /set safeboot, and bulk vssadmin.

2. Removal (If You Spot It Early)

Step-by-step “contain, clean, validate” workflow:

  1. Isolate the affected hosts immediately: pull network cables, disable NICs, log off VPNs.
  2. Identify the payload PID (often blackcat.exe or alph.exe with random 10-char names) using Get-Process or EDR.
  3. If Windows Safe Mode not already triggered, boot to WinRE or off-line media → run recovery disk with Windows Defender Offline or Malwarebytes Rescue Kit.
  4. From Safe Mode or WinRE:
    • Delete registry persistence (HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run, random GUID task scheduled under schtasks /query /fo LIST >> persistence.txt).
    • Remove scheduled tasks grunt, svc2, rdsvc, etc.
    • Inspect ExtFS-compatible VMs as well (/var/spool/cron, /etc/rc.local).
  5. Forensic evidence: capture RAM dump before shutdown for legal teams.
  6. Rebuild rather than “repair” for domain controllers, file servers, and critical ERP machines. Patch offline, then join to isolated network segment for rebuild verification.

3. File Decryption & Recovery

  • Feasibility: No public decryptor exists (uses ChaCha20 + RSA-4096, private keys controlled by affiliates).
  • Decryption Avenue 1 – FBI keys (Dec-2023 takedown): FBI seized 500+ decryption keys; victims who still hold encrypted files should upload file pair (cipher + plain) plus ransom note to https://www.ic3.gov/Decryptor.
  • Paywall choice: BlackCat/ALPHV provides web-UI chat; reporting structure mandates US victims evaluate OFAC sanctions before any payment. Strongly recommended not to pay under new OFAC bulletin unless expressly cleared.
  • Alternative recovery ≥90 % of files rely on offline backups; if immutable backups exist, forensic teams restored 250 TB+ in 72 h average downtime.

4. Other Critical Information

  • Cross-platform reach → Only major Rust-written ransomware that natively targets ESXi, Synology, FreeBSD; expects --vm-snapshot argument to fork virtual disks.
  • Public extortion → Nov 2023 ALPHV affiliate created “searchable leak portal” with custom filter; do not store plaintext on public shares—they index every share name explored.
  • Ransom note content: dropped as RECOVER-[hash]-NOTES.txt, includes Tox ID (`7C3C39E12613906A47”) and One-Time-Secret URL plus fresh QR Code per victim.
  • Insurance impact: BlackCat threat actors repeatedly urge companies to hide events from cyber insurers; insurers started adding retroactive non-payout clauses tied to RDP exposure after Q3 2023.

Useful Links & Tools
• Patch Tuesday Tracker – https://msrc.microsoft.com
• FBI Recover Keys Portal – https://www.ic3.gov/Decryptor
• ESXi BlackCat IoCs – VMWare advisory VMSA-2023-0012
• CrowdStrike Falcon OverWatch BlackCat Playbook – requires entitlement

Stay vigilant: BlackCat’s affiliate program means tactics evolve monthly. Maintain regular incident-tabletop exercises with recovery measured against realistic RTO/RPO metrics.