cryptbit

[Content by Gemini 2.5]

📋 cryptbit Ransomware Intelligence Brief

🔍 Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    Encrypted files are renamed with the .cryptbit suffix appended directly after the existing extension.
    Example: Report.xlsx → Report.xlsx.cryptbit

  • Renaming Convention:
    Original filename and internal directory structure remain unchanged; only the extra suffix is added. After encryption, a companion ransom note called !!_info-decrypt.txt is dropped into every affected folder.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First observed at scale during mid-January 2023. Larger campaigns peaked between February and April 2023, with continuous but lower-volume waves through Q3 2023.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Remote Desktop Protocol (RDP) brute-force & credential stuffing – Most widespread initial access observed to date.
  2. ProxyShell / ProxyLogon chain – Active exploitation of unpatched Microsoft Exchange servers (CVE-2021-34473, CVE-2021-34523, CVE-2021-31207).
  3. Phishing with ISO or IMG attachments – Macro-laced documents dropping a first-stage loader.
  4. Software supply-chain abuse – Compromised MSP tooling (AnyDesk, ScreenConnect) leveraged for lateral deployment.
  5. Smishing & spear-phishing – SMS-based lures directing users to fake VPN or “security-update” sites that trigger drive-by downloads.

🛠️ Remediation & Recovery Strategies

1. Prevention

  • Baseline Hardening Steps
    • Switch RDP from default port 3389; enforce network-level authentication (NLA) and lock-out policies (≤3 attempts).
    • Require MFA for all external logins—RDP, VPN, OWA.
    • Rapidly patch Exchange, Windows, and VPN appliances—especially the ProxyShell trio.
    • Filter or quarantine .iso, .img, .vhd attachments at the mail gateway and apply Microsoft “Mark-of-the-Web” (MotW) propagation rules.
    • Segment local admin accounts—no reuse between servers & endpoints.
    • Deploy application whitelisting (Windows Defender ASR/WDAC or third-party EDR blocking unsigned payloads).
    • Add behavioral-detection rules in your EDR that fire on vssadmin delete shadows /all, bcdedit /set safeboot and similar destructive commands.

2. Removal

  • Step-by-Step Cleanup Guide
    ‎1. Disconnect from network immediately to halt lateral spread.
  1. Identify active process(es): Samples often drop as %ProgramData%\csrss\flt.exe or similar; look for unsigned binaries launched from %TEMP% or %APPDATA%.
  2. Boot into Safe Mode with Networking.
  3. Run reputable removal tools:
    • Microsoft Defender Offline Scan
    • Sophos “HitmanPro Kickstart” or ESET’s rescue media
    • Kaspersky’s free TDSSKiller for rootkit clearing
  4. Delete persistence artifacts:
    • Scheduled tasks in Task Scheduler Library/Microsoft/Windows/Crypt (misc)
    • Registry keys under HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run pointing to %APPDATA%\[random]\crypt.exe
  5. Reset strong passwords for every local and domain account touched.
  6. Reboot into normal mode and confirm the infection bucket is clean via fresh AV/EDR full scan.

3. File Decryption & Recovery

  • Recovery Feasibility:
    At time of writing (latest samples, June 2024), cryptbit is NOT decryptable for free. Its core encryption routine uses ChaCha20 + RSA-4096, and each system receives a unique RSA key pair encrypted with the attacker-controlled public key. Consequently, a workable offline decryption tool does not exist.

  • Essential Tools / Processes:
    • Offline backups (immutable, air-gapped and test-restores) remain the single reliable path to recover.
    • Volume Shadow Copies are routinely wiped (vssadmin delete shadows /all), but an offline VHD snapshot or SAN-level replication snapshot may be intact if the ransomware can’t reach the hypervisor.
    • Restore Windows services via DISM /RestoreHealth if system files have been tampered with.

4. Other Critical Information

  • Unique Characteristics:
    • cryptbit shuts down Windows Volume Snapshot Service (VSS) at process start-up—even before encryption begins.
    • Uses multi-threaded, fast-queue encryption which can encrypt a 1 TB file share in ~30 min on SSD/HDD arrays.
    • Drops a second-stage info-stealer (Telegram channels term it “cbit-dump”) that exfiltrates *.kdbx, *.rdp, *.ppk files before final encryption—raising both extortion risk and regulatory notification obligations.

  • Broader Impact & Notable Incidents:
    • Most heavily damaged verticals include regional hospitals in LATAM, UK municipal councils, and North-American manufacturing SMEs.
    • Average ransom demand is 0.85 BTC (≈ USD 31 k as of 04/2024) with a 72-hour deadline.
    • Data-leak portal (“cryptleaks”) posted 11 victims in March 2024, totaling ~4 TB of stolen documents.

🔔 Take-Action Checklist Today

  1. Confirm your Exchange server is on March 2023 CU or newer—including the ProxyShell backports.
  2. Review backup integrity (3-2-1 rule) and DR runbook—restore test against a clean VM.
  3. Enable network segmentation for RDP (block 3389 on WAN unless via VPN & jump-box).
  4. Push GPO to block email delivery of .iso and .img attachments if not already enforced.
  5. Validate that EDR can detect by running an open-source cryptbit sample in an isolated sandbox (MalwareBazaar hash: 8e5e6b1e89b90eccab87dc656b0b5154).

Stay vigilant & share the knowledge—together we reduce the success rate of cryptbit and similar strains.