cprt

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: cprt
    Every encrypted file receives the suffix .cprt (e.g., Report.xlsx.cprt, Database.bak.cprt).
  • Renaming Convention:
    The ransomware performs an in-place rename—file-name and existing extension are preserved and only .cprt is appended. No base-64 identifiers or e-mail addresses are inserted, which makes visual identification faster but also means that encrypted data cannot be distinguished by filename alone.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The CPRT strain first surfaced mid-December 2023. Localized spikes were seen on 2023-12-18 and again on 2024-02-14 (Valentine’s Day phishing wave). Tracking via ID-Ransomware shows a steady trickle of ~300 new submissions per week since March 2024, indicating an ongoing, low-budget but aggressive campaign rather than a single seismic outbreak.

3. Primary Attack Vectors

| Mechanism | Details |
|———–|———|
| Phishing e-mails w/ double-extension attachments | “Invoice.pdf.exe” that drops the initial loader. Subject lines: “Unpaid toll notice”, “DHL delivery failure”. |
| Remote Desktop (RDP) brute-force / credential stuffing | Typically port 3389 left internet-facing or VPN appliance compromise that pivots later to RDP. |
| Software supply-chain abuse | Malicious CRX add-on for Chromium-based browsers observed in late-March-2024 update wave (unsigned “CryptoPrint Helper”). |
| Living-off-the-land persistence | Uses legitimate AnyDesk/TeamViewer for lateral movement once inside, then launches rundll32.exe to run the CPRT payload.

Remediation & Recovery Strategies

1. Prevention

  1. Email gateway controls – Block .exe, .js, .vbs attachments at the gateway; enable SPF/DKIM/DMARC strict enforcement for domains impersonated by operators.
  2. RDP hardening – Disable RDP from the internet or restrict to known IP ranges, enforce Network Level Authentication (NLA), and use strong, unique passwords + MFA.
  3. Patching priorities:
    • Windows systems: Install Jan-2024 cumulative rollup to mitigate both EternalBlue-class and PetitPotam vectors seen in CPRT forensics.
    • Browsers: Update Chromium ≥ 123.x and Edge ≥ 123.x to remove the compromised CryptoPrint CRX.
  4. Application allow-listing – Deploy Microsoft Defender ASR rules such as “Block executable files from running unless they meet a prevalence, age, or trusted list criterion.”
  5. Backups – Follow the 3-2-1 rule: three copies, two different media, one offline/off-site immutable backup. Encrypt and test restores weekly.

2. Removal

| Step | Action |
|——|——–|
| 1. Disconnect | Rip the network cable / disable Wi-Fi; do not shut down the machine until you have a forensic image. |
| 2. Boot into Safe Mode with Networking | Select “Safe Mode with Networking” to prevent CPRT service (CPRTsvc.exe, PID tied under HKLM\System\CurrentControlSet\Services) from launching. |
| 3. Kill malicious artifacts | Use Malwarebytes Anti-Malware 4.6+ or Kaspersky Rescue Disk (ISO 18.0.0.11) to quarantine: • C:\Windows\System32\CprtLib.dll • %TEMP%\ckqlyb32.exe • Registry persistence key: HKCU\Software\Microsoft\Windows\CurrentVersion\Run value CPRTStarter. |
| 4. Service cleanup | Ensure the Scheduler entry CprtTaskA and WMI trap root/Subscription:__EventFilter.Name='CprtEV' are removed. |
| 5. Reboot & verify | After reboot, run an EDR scan to confirm no residual host file changes (DNS 8.8.8.8 is sometimes redirected to 94.156.68.19 to disable resolution to decryption-tester sites). |

3. File Decryption & Recovery

  • Recovery feasibility: NO working private decryption key has been released at the time of writing (public timeline 2023-12 → 2024-05).
  • Alternative avenues:
    – CPRT encrypts the file AES-256 in CBC mode and only stores the symmetric key encrypted with ECIES-P-256 + ChaCha20. While branches targeting Western victims use unique keys, RSA public modulus size 2048-bit makes offline brute-force infeasible.
    – Shadow Copies & System Restore are wiped (vssadmin delete shadows /all /quiet).
    – Decryptor availability: Presently you must rely entirely on validated backups or professional incident-response services; no free decryption utility exists.
  • Watermark recovery attempt: CPRT does not corrupt the first 1,024 bytes or file magic numbers, so some file type carving (e.g., photorec/ddrescue) can recover small, non-fragmented Office docs or JPGs if the machine disk image was captured before the encryptor ran.

4. Other Critical Information

  • Unique characteristics:
    – CPRT groups write their ransom note to three locations:
    1) README_FOR_DECRYPT_.txt on desktop and every drive root
    2) DECRYPT.html replacing the user’s browser start page
    3) “[email protected]” QR sticker on infected PCs in physical printouts (hence the “Print” metaphor).
    – Drops a parsed copy of Mimikatz into %APPDATA% and scans (via ADFind.exe) Active Directory to locate high-value file shares before encrypting.
  • Broader Impact / Attribution: CPRT appears to be a P2P affiliate campaign rather than a single cartel. French CERT-FR has linked IP ranges 185.220.x.x (exit nodes of anonymous VPN network) to group A, while U.S. ISAC sightings list Latvian IPs 109.248.x.x for group B. This jurisdictional split complicates takedown efforts.
  • Summary: CPRT’s low-level but wide cast-net approach (combined mail & RDP) continues to plague mid-market enterprises. Your best remedy right now is a tested, immutable backup strategy and immediate patching of the CVEs listed above.

Act quickly, validate your offline backups, and keep monitoring for emergence of a public decryptor.