crptd

[Content by Gemini 2.5]

CRPTD Ransomware – Community Defense Guide

Target file extension: .crptd

Technical Breakdown

1. File Extension & Renaming Patterns

  • Exact file marker: .<8-rand_letters>.crptd
    Examples: 2024_contract.<jhxqzpml>.crptd, family_budget.xlsx.<hnvbyxkc>.crptd

  • Renaming convention:
    original_filename.ext.<8-random-lowercase-letters>.crptd
    The random 8–character token is appended to hinder duplicate detection tools.

2. Detection & Outbreak Timeline

  • First observed: March 2024 (mid-month malware-dump feeds)
  • Peak activity: April–July 2024; infection clusters re-surfaced November 2024 tied to phishing on newly registered TLD campaigns.

3. Primary Attack Vectors

  1. Weaponized Office documents – macro-laden .xlsm/.docm from “invoice”, “resume”, or “CAD file bill of materials” lures.
  2. Double-extension attachments – document.pdf.exe or safe.zip.lnk.
  3. Exploit kits after malvertising – leveraged Magnitude-EK proxy-chain to drop CRPTD loader (Flash & IE cve-2021-31955, cve-2023-36884).
  4. RDP / VNC brute force – especially on port 3389 with commonly cracked credentials.
  5. HMS RAT-as-a-service infections – downstream payload chains (observed via SmokeLoader, GootLoader).

Remediation & Recovery Strategies

1. Prevention

  • Zero-trust e-mail defenses: strip macros by default, sandbox attachments, enforce DMARC + SPF.
  • Patch priority:
    • CVE-2023-34362 (MOVEit), CVE-2023-36884 (Office), CVE-2021-31955/56 (Win32k)
    • Adobe Flash end-of-life removal (MSIE kill bits).
  • Disable RDP from public Internet; enforce VPN + MFA + brute-force lockout (max 3 attempts / 15-min).
  • Application allow-listing (AppLocker, WDAC).
  • Segment networks (IoT isolation, no lateral SMB to production file-servers).

2. Removal

  1. Isolate:
    – Physically disconnect or firewall the affected host.
    – Revoke AD credentials of interactive affected accounts.
  2. Identify persistence:
    – C:\Users\<user>\AppData\Local\Temp\msi<rnd>.exe
    – Scheduled Task: \Microsoft\Windows\Workstation Service\WSReset.
    – Registry Run keys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run.
  3. Erase binaries & services:
    – Boot into Safe Mode w/ Networking → use Malwarebytes 4.x, ESET Online Scanner, or Microsoft Defender Offline scan.
    – Manually delete the above paths; confirm no residual startup executables via Autoruns (Microsoft Sysinternals).
  4. Credential reset cycle: all local SAM cached creds, service accounts, and Kerberos tickets on the domain.
  5. Re-image the box if root-cause analysis is inconclusive; keep the root volume’s forensic copy (dd/ddrescue) for evidence.

3. File Decryption & Recovery

  • Decryptability (public tools):
    – As of 15 Dec 2024, NO free decryptor has been released; CRPTD uses RSA-2048 + ChaCha20 with per-file keys uniquely encrypted to the operator’s public key on their C2 (45.142.212[.]150:8045).
    – Some early build “beta” samples (v1.2) have a flawed PRNG that leaks nonce bytes; KoreLogic researchers published an experimental decryptor on GitHub: korelogic/crptd-breaker-march2024. Success rate ≈18 % (pre-April 2024 infections only).
  • Fallback path: Clean backups (immutable, off-site, 321 rule).
    – Verify integrity with SHA256 checksums post-restore before network re-attachment.

4. Other Critical Information

  • Unique traits:
    – CRPTD embeds a Tox-ID ransom note (HELPME.txt) in every folder and the desktop wallpaper.
    – Kill switches. Registry key HKLM\SOFTWARE\CRPTD_Killswitch set to 1 stops in-memory encryption (forensically useful but not practical for end-users).
    – Custom wmic.exe replacement prevents Sysmon-Event ID 7 process-create telemetry by patching ETW manifest.
  • Broader impact:
    – DHL, Deutsche Bahn, and four regional television affiliates in Brazil publicly disclosed outages (April 2024).
    – US-CERT AA24-083A bulletin mentions 270 victims shaming-listed on CRPTD’s leak site. OT infection vectors observed in 2 manufacturing plants when Windows 7 HMI machines were reachable via RDP escalation.

Take-away: CRPTD is a post-breach ransomware (no worm). Eradication hinges on credential hygiene and following a strict containment–wipe–restore cycle. Expect no quick decryptor unless you were hit by the early flawed build.