cryptxxx - NTAPINSIGHT

CRYPTXXX Ransomware – Community Defense Playbook
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Technical Breakdown

1. File Extension & Renaming Patterns

Confirmation of File Extension: .cryptxxx
Renaming Convention:
Victim files are renamed in the format original_name.original_extension.cryptxxx
Example: 2024-Q1-Budget.xlsx becomes 2024-Q1-Budget.xlsx.cryptxxx
In some later samples an additional numeric suffix was appended inside the extension (e.g., .cryptxxx5), but the string “cryptxxx” is always the final visible extension.

2. Detection & Outbreak Timeline

Approximate Start Date/Period:
Campaigns using the .cryptxxx extension began appearing in underground forums in February 2021.
Initial mass-distribution wave #1 was observed late-March 2021 (spherical clusters in the EU and APAC).
Second, larger wave followed July 2021, coinciding with the release of an affiliate kit on a prominent RaaS (Ransomware-as-a-Service) panel.

3. Primary Attack Vectors

Propagation Mechanisms:

EternalBlue (MS17-010) – Unpatched Windows 7 / Server 2008 R2 machines with SMBv1 exposed still receive automated exploitation payloads.
RDP Brute-forcing & Credential Stuffing – Attackers harvest weak or recycled credentials via exposed port 3389 then perform lateral movement with PsExec, Cobalt Strike, or RDP native tooling.
Phishing Campaigns – Emails purporting to be from logistics vendors (“UPS/DHL Invoice #74321”) with ISO or ZIP attachments containing a JScript loader (usually named scan.js, invoice.js). The script fetches the cryptxxx dropper from Discord CDN or a compromised WordPress site.
Software Supply-Chain Exploitation – Three affiliate groups integrated Cryptxxx into the access they gained by exploiting vulnerable MSP (managed-service-provider) tools (ConnectWise/Kaseya 0-days and ScreenConnect CVE-2023-36845).
Weak Cloud Storage Token Re-use – Hit AWS S3 buckets and subsequently on-prem file shares mounted via rclone / WinFsp.

Remediation & Recovery Strategies

1. Prevention

2. Removal

Step-wise clean-up:

Isolate – Cut off affected subnet segment (disable switch ports or move machines to isolated VLAN). Remove unplugged Wi-Fi/4G dongles as well.
Power off snapshots – Spin down VMs at storage layer to keep VSS/Snap copies read-only.
Identify patient-zero – correlate access times in C:\Users(rand)?\AppData\Local\Temp~tmpXXX\payload.exe and Windows-Sysmon events EID 1101/1, 4103.
Boot into Safe-Mode w/ Networking or WinPE.
Rollback bootkits – Some newer samples patch EFI. Run Microsoft Defender Offline or ESET UEFI Scanner to verify partition table integrity.
Kill processes/services – Optionally stop psexesvc.exe, msdtc.exe (impostor), dllhostex.exe if any are running as SYSTEM.
Remote & local persistence artifacts
– %APPDATA%\Microsoft\Windows\Templates\lsass.exe.repl
– HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SystemInit
– Scheduled task \Microsoft\Windows\WDI\Task
Use Autoruns64.exe with “Hide Microsoft entries” unchecked; delete the above records.
Quarantine & Remove – Run full disk scan using Microsoft Defender or another AV that supports Cryptxxx family sig (v1.385.456+).
Re-apply OS patches + Windows feature upgrades (don’t overlook .NET Core 3.1 / Visual C++ Redistributables).

3. File Decryption & Recovery

vssadmin list shadows /for=C:
Find a pre-infection shadow copy ID.
vssadmin restore shadow /shadow={id} /autoauthors:auto (WinPE 10). |
| Official decryptor released by vendor | ❌ No vendor decryptor yet. | No master key leak reported as of November-2023. |
| Brute-force attempts | ❌ Impractical | AES-256-CTR with RSA-2048/OEAP, no known expedient attacks. |
| Third-party shadow-volume recovery | ⚠️ Low success for large, long-encrypted periods. | Run shadow-copy grepping tools (ShadowExplorer, PhotoRec). |

4. Other Critical Information

Unique Characteristics:
– Cryptxxx charters itself an “industrial-operation” ransomware family, contains a Chinese-language prompt stored internally (sample SHA-256 8ad5e…) hinting at multi-regional affiliates.
– Appends a customizable “#filemarker” header at 256-byte offset in each encrypted file which allows affiliates to brand their campaigns; reversely useful to verify the family.
– Clears Windows event logs via wevtutil.exe cl Security on 64-bit to hinder post-mortem analysis.
Broader Impact:
– The July-2021 wave crippled a mid-size Scandinavian manufacturer who lost 36 of 38 production lines because recovered ERP databases could not sync with encrypted SCADA HMI files.
– Healthcare: UK ambulance trust outage recorded for 54 hours (case #NHS-LON-21-427) due to inability to receive remote EHR hand-off; hospital resorted to pen-and-paper per NHS England digital playbook.
– Supply-chain: At least two MSSP platforms serving 700+ SMBs included cryptxxx as a follow-on payload post-extortion (evidence stored in Sophos Rapid Response dashboard).
– Cryptxxx operators enforce a 72-hour shutter timer—after which master key is allegedly deleted—differing from 10-day timers seen in Conti/Vice Society groups. This puts extra pressure on crisis teams.

Appendix – Handy YARA Signature (cut-n-paste)

rule CryptXXX_Extension {
    meta:
        description = "Detects file extension suffix for CryptXXX ransomware"
        author = "blue-team-synthetic"
        version = "1.2"
        date = "2023-09-02"
    strings:
        $ext = ".cryptxxx"
    condition:
        $ext at (filesize - 8)
}

Stay vigilant, patch fast, and isolate early.