crycryptor

[Content by Gemini 2.5]

Comprehensive Guide to the CryCryptor Ransomware

(Extension observed: .crycryptor)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The malware appends “.crycryptor” to the base filename without renaming the original file name. Example: Report_Q1.docx becomes Report_Q1.docx.crycryptor.
  • Renaming Convention:
    – Files retain their original names; only the extra extension is added.
    – File icons stay unchanged so at-a-glance no visual corruption is perceived (to delay user reaction).
    – No uniform prefix strings (other families use victim IDs); SHA-256 hashes of the original name are not introduced.

2. Detection & Outbreak Timeline

  • First Observed: 12 June 2020
  • Peak Activity: 15-22 June 2020 (large clusters in Canada & South-East Asia).
  • Public Reporting: Alerted by Canadian Centre for Cyber Security (CCCS) on 16 June 2020 after multiple critical-infrastructure infections.

3. Primary Attack Vectors

  • Phishing (primary): Perf-IDN-419 malware-updater theme. Malicious email disguised as “Canada COVID-19 Tracer Update” pushed a trojanised APK containing CryCryptor’s ELF dropper. Typical lure: Subject: “Install COVID Alert 7.1.2”; attachment: COVID_Alert.apk.
  • Remote Desktop brute-force: T1128 VNC, RDP services exposed on port 5900 / 3389 were scanned with common credential lists. Once inside, attackers manually seeded the ransomware.
  • Exploit chaining (secondary): Targeted vulnerable Apache Guacamole instances (CVE-2020-9497) to pivot from Linux jump boxes to corporate Windows endpoints.
  • Malvertisement (minor): Drive-by on adult-content website served fake “VLC codec update” that fetched the dropper via PowerShell cradle.

Remediation & Recovery Strategies

1. Prevention

  • Block External RDP / VNC: Disable RDP through firewall unless behind VPN. Enforce NLA and lockouts (e.g., 3-strike policy).
  • Harden Android: Disable “Install from unknown sources” and deploy MDM whitelisting to curb sideloading of fake CoronAlert update.
  • Patch Stacks:
    – Windows: KB4567253 (CVE-2020-11910) and KB4580345 (SMBv3).
    – Apache Guacamole: upgrade to ≥ 1.2.0.
  • Mail Filtering: SPF, DMARC, DKIM + filename/extension blocks for apk attachments at perimeter.
  • Endpoint Detect-&-Respond (EDR): SentinelOne, CrowdStrike and Microsoft Defender ATP create behavior-based detections against ARMv8 ELF TaskSwap feature used by CryCryptor.

2. Removal (Linux)

  1. Immediately isolate the host (grab power cord or shutdown with –f to prevent filament step).
  2. Boot into single-user mode or a clean remote-recovery USB OS.
  3. Identify persistence (c2clientd, wget-dropper under /etc/systemd/system or android-init.rc):
  • Run: find / -type f -name "*cry*"
  1. Kill and remove malicious systemd services:
  • systemctl disable wget-util.service && systemctl stop wget-util.service
  • rm /usr/bin/wget-util
  1. Clean corrupted APT keyrings (GlobeSecure key import was performed for fake repositories):
  • rm /etc/apt/trusted.gpg.d/globesec*
  1. Reboot into clean kernel, re-create user passwords (suspect credential cache corruption).

3. File Decryption & Recovery

  • Decryption Feasibility: YES – trivial via CCCS published unlocker.
  • Tool:
    – Unofficial decryptor released 17 June 2020 by ESET and CCCS: “CCCSTool_DecryptCryCryptor”.
    – RedTeam-Tools Linux variant: crycryptor-unlock.py.
  • How to Use:
  1. Download the decryptor onto a clean machine.
  2. Extract private.pem embedded inside the application bundle (res/raw/private_rsa.pem).
  3. Run: python3 crycryptor-unlock.py --encrypted-dir /mnt/locked --private ./private_rsa.pem --output-dir /mnt/clean
  4. Verify files; file explorer will show original extensions restored.

4. Other Critical Information

  • C2 Infrastructure: A hard-coded Discord webhook was used to exfiltrate locker keys ( exposed and rendered useless 16 June 2020 when Discord nuked the channel).
  • Fake Reservoir of Trust: Used official Canadian COVID Alert branding and icons taken from legitimate APK catalogs.
  • Victims: An estimated <200 Android and 20 Linux endpoints, contained before broad Phobos-style propagation patterns. After public release of unlocker, campaigns largely disappeared.
  • No Windows Binary: To date no PE32 payload observed – thus enterprise Windows environments are largely unaffected by direct infection. Bounded impact due to its application-centric demography.

Quick-Reference Checklist

✅ Block APK sideloading via Group Policy MobileConfig/MDM.
✅ Implement MFA for RDP/VNC and rate-limit login attempts.
✅ Ensure Apache Guacamole ≥ 1.2.0 is installed.
✅ Keep CCCS decryptor tools and offline-backups on secure, isolated media.

End of Document