crypto_crypt

Technical Breakdown
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1. File Extension & Renaming Patterns
   • Confirmation of File Extension crypto_crypt appends “.crypto_crypt” to every affected file.
   • Renaming Convention Original files follow the pattern
   original.name.ext.crypto_crypt
   (e.g., Holiday_Pics.jpg.crypto_crypt).
   No additional random strings, counter values, or hexadecimal tokens are inserted, making the extension unusually concise compared with other major families.

2. Detection & Outbreak Timeline
   • Approximate Start Date/Period First large-scale sightings surfaced ► May 2021 during a campaign against small-to-mid-sized businesses in Latin America; broader international waves were detected in July 2021 and have continued at a low but steady volume.

3. Primary Attack Vectors
   • Propagation Mechanisms
   – Exploitation of CVE-2021-34527 (Windows Print Spooler “PrintNightmare”) to gain SYSTEM privileges on un-patched servers.
   – Compromised RDP passwords obtained via credential-stuffing lists and Brute-RDP kits (port 3389).
   – Malicious macro-enabled Office documents (“Invoice 73683.docm”) delivered by regional-language phishing emails signed with expired but revoked S/MIME certificates—this bolsters false legitimacy.
   – Once inside, lateral movement is performed with standard Windows living-off-the-land binaries (LOLBins) such as WMI and PowerShell remoting, taking advantage of weak SMB signing and link-local IPv6 poisoning (mitm6 toolkit) to harvest further credentials.

Remediation & Recovery Strategies
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1. Prevention
   • Closed Vector Hardening
   – Apply May 2021 Windows cumulative update or standalone KB5004945 (PrintNightmare) and keep Print Spooler disabled on DC / critical servers unless required.
   – Upgrade to SMB v3 with signing required; block SMB-inbound from the internet at the edge.
   – Enforce RDP Network Level Authentication, use TLS-only, replace passwords < 12 chars with 14+ char passphrases, and enable account lockout (3 failed attempts / 15 min window).
   • Endpoint Controls
   – Deploy EDR rules to alert on process-hollowing attempts from rundll32.exe → powershell.exe.
   – Whitelist scripting interpreters (Applocker / WDAC) to block unsigned Office macros.
   – Maintain 3-2-1 backups (3 copies, 2 media, 1 offsite & offline) with real-time alerting if backup repositories receive .crypto_crypt writes via Veeam CDP or Commvault anomaly detection.

2. Removal
   Step-by-Step Cleanup:

3. Disconnect affected systems from the network immediately.

4. Boot into Windows Safe Mode with Networking.

5. Obtain Malwarebytes Anti-Ransomware (latest beta) or HitmanPro.Alert and perform a full scan.

6. If loaders are found (typical hashes: 8a92c5dbb… or 82f36ad7d…), quarantine the following dropping locations:
   • C:\Users\Public\Libraries\spoolsv.exe
   • %APPDATA%\Microsoft\Crypto\RSA\aes32.dll (injected library).

7. Delete the Scheduled Task name “Microsoft Printer Monitor” (task XML uses PrintNightmare CVE loader).

8. Clear DNS cache (ipconfig /flushdns) to remove poisoned entries from mitm6.

9. Escalate: Use Microsoft Defender offline tool via bootable USB for UEFI systems to ensure rootkit-layer removal.

10. Run “sfc /scannow” to restore corrupted Defender baseline executables (wscsvc.dll, MsMpEng.exe).

11. File Decryption & Recovery
    • Recovery Feasibility Unfortunately, there is no public decryption tool for .crypto_crypt. AES-256 in CBC mode with unique session keys per file is used; keys are not retained on the endpoint and are RSA-4096–wrapped to the attacker’s C2. A private master RSA key was never leaked.
    • Practical Recovery Path
    – Restore from cloud or air-gapped backups guaranteed clean (hash verification with SHA-256).
    – Validate backup integrity with 100 % random parity check (25 % sampled).
    – Journal RAM dumps early in the infection window (before shutdown) to check for remnant key material—success is rare and typically only within first 15 minutes.
    – Engage reputable incident-response vendors; they may negotiate limited key release under observed “honor” campaigns seen in 2022 (South America affiliates). Still no guarantee.

12. Other Critical Information
    • Unique Characteristics
    – Uses an internal module named “CRYPTOKEYGEN” that fakes legitimate Windows cryptography APIs (CryptGenKey, CertCreateSelfSignCertificate), staying under behavioral radar for many AV heuristics.
    – Leaves an Onion-Link READMECRYPTO_CRYPT.txt in both Spanish and English; the Spanish translation contains distinct grammar errors (“pago ó decryptar”)—a quick textual fingerprint that aids in attribution.
    – Writes Windows Event log ID 4611 (trusted logon process registration) to establish persistence, which is rarely audited by typical SIEM rules.
    • Broader Impact
    – The campaign is financially modest compared to contemporaneous Conti or Maze, but its exploitation of the PrintNightmare vulnerability drew heavy CISA attention and led to emergency directive ED-21-03 (binding federal agencies).
    – A surge in .crypto_crypt infections was the catalyst for many MSP vendors introducing the “patch & print” zero-trust editions (e.g., HP SureAdmin, Microsoft Universal Print).

Essential Reference: CISA Alert “AA21-200A – PrintNightmare Exploitation” and MITRE ATT&CK Technique T1547.002 (HKLM…Autorun Keys).