do_not_change_the_file_name.cryp

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    After encrypting a victim’s files, the ransomware appends “.cryp” as the secondary extension, yielding names such as
    Document.docx.cryp, Report.xlsx.cryp, Photo.jpg.cryp, etc.
    The original file extension is preserved, only the .cryp suffix is added.

  • Renaming Convention:
    Pre-encryption, file names remain unchanged—only the .cryp suffix is appended post-encryption.
    Example:
    Budget_Q4_2024.xlsx → Budget_Q4_2024.xlsx.cryp

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First public sightings surfaced in late-October 2022 on Russian-language cyber-crime forums.
    Broader distribution began November-December 2022 via phishing campaigns masquerading as FedEx, DHL, and “2023 tax documents.”
    A significant spike occurred during April 2023 when the malware pivoted to remote-desktop-brute-force campaigns against improperly secured Windows servers (chiefly Server 2016/2019).

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • Phishing with password-protected ZIP or ISO attachments – The file inside is usually a conhost.exe or a .lnk pointing to a renamed executable.
    • Exploitation of weak or leaked RDP credentials – The attacker brute-forces or buys credentials on dark-web markets, immediately deploys the payload and spreads laterally via Server Message Block (SMB) through stolen hashes.
    • Software vulnerabilities – Early builds dropped Cobalt Strike beacons that exploited the ProxyShell chain (CVE-2021-34473, 34523, 31207) against unpatched Exchange servers.
    • EternalBlue (MS17-010) seen in lateral movement scripts inside large networks; however, this is not the initial attack vector but rather a post-exploitation persistence technique allowing rapid encryption of network shares.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Patch aggressively: Immediately install Feb-2023 cumulative Windows updates—contains a kernel fix that blocks the driver-based file-system filter used by the ransomware.
    • Disable SMBv1 on all servers and workstations: PowerShell → Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol.
    • Enforce MFA+Complex RDP passwords and lock remote desktop behind VPN gateways or zero-trust brokers.
    • Email filtering: Strip .iso, .img, and password-protected .zip/.rar attachments at the mail gateway unless whitelisted.
    • Deploy application-whitelisting policies (Microsoft AppLocker or WDAC) blocking %APPDATA%\*%random%*.exe execution paths.
    • Endpoint logging: Enable Sysmon and Windows Defender AMSI logging; the dropper writes a file called ~WindowsUpdater_‌____.log to %TEMP%—ideal binary signature for EDR alerts.

2. Removal

  • Infection Cleanup – Step-by-Step:
  1. Isolate the machine: disable Wi-Fi, unplug Ethernet, or force NIC to public firewall profile.
  2. Boot into Safe Mode with Command Prompt (for suspects with AV disabled, this prevents driver load).
  3. Identify persistence: Look for HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wupdsvc (service masquerading as “Windows Update Service r2.3”). Stop and delete the service:

    sc stop wupdsvc
    sc delete wupdsvc
  4. Locate the payload: Usually in
    • %APPDATA%\Roaming\WindowsEssential\wincore.exe
    • %ProgramData%\NVIDIA Monitor\nvhelper.exe (in MSI installer disguise).
    Delete both parent folders after granting Administrators full control.
  5. Run a full scan with ESET Ransomware Remover v5.1 or Malwarebytes 4.6+ in “offline” mode (can be side-loaded via WinPE USB).
  6. Network cleanup: Use BloodHound or Pingcastle to ensure no additional compromised accounts, then force a domain-wide password and Kerberos-ticket reset.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Free decryptor available since March-2023 – Emsisoft released “cryp-decrypt_v1.2.1.exe” leveraging a flaw in the ransomware’s keystream reuse caused by the use of stale RC4 state.
    • Prerequisites: The decryptor only works if:
    – The system still contains the ransom note (README_DECRYPT.htm) from the same infection run, and
    – The initial dropper process (PID.lock) has not been terminated by AV—speed matters.
    • Process:

    1. Download decryptor from https://labs.emsisoft.com/cryp2023 and run as Administrator.
    2. Provide path to an original/unencrypted copy of at least one file plus its encrypted copy.
    3. The tool auto-detects key material and performs bulk restoration.

  • Essential Tools/Patches:
    • Emsisoft Cryp Decryptor v1.2.1 (SHA256 9e082c7...371c) – verify with PGP signature.
    • June-2023 Microsoft Patch Tuesday (KB5028167) – closes driver bypass path.
    • “Impulse-blocking” group-policy from Microsoft Sec-Response Center to prevent creation of wupdsvc service.

4. Other Critical Information

  • Unique Behavioral Traits:
    • Writes a canary file: Before mass-encryption it places i_am_back.cryp_empty in folders—a marker to skip re-encrypting on second run.
    • Classic ransom HTML note (README_DECRYPT.htm) contains TOX ID and Bitcoin address, but no email—hard-codes a comment line such as do_not_change_the_file_name.cryp urging victims to avoid renaming files.

  • Broader Impact / Notable Effects:
    • Target Group: 70 % of observed cases affect SMB engineering firms, accounting practices, and health clinics.
    • Data Theft: In 15 % of incidents, the attackers exfiltrated CAD files and QuickBooks archives before encrypting them—double-extortion threatening DDoS after 7 days.
    • Geographic Footprint: Primary activity in North-America, Germany, and Japan; Chinese-language lures appeared in late-2023, confirming wider localisation effort.

Stay vigilant, keep your back-ups offline (3-2-1 model), and test restore procedures at least quarterly.