cryakl

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    The ransomware family known as Cryakl originally added the literal suffix .cryakl (or uppercase .CRYAKL) to every encrypted file and has since added secondary email-based extensions that look similar, e.g.:
    .lockcryakl@[attacker-domain].com
    The root “cryakl” string remains, so any of the above variants are symptomatic of Cryakl infection.

  • Renaming Convention:
    Before encryption, files are triple-compressed and AES-128 encrypted in memory. The resulting file is renamed thus:
    original.name.sha1-hash-of-filename.cryakl
    Example:
    Report Q4.xlsx.520c2104eacc6e5f8f35a9f5b67719a0b4e4d2bf.cryakl
    Every subsequent infection repeats this SHA-1 + extension logic.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    • Spring 2014 – first samples submitted to VirusTotal under “Crystal/Cryakl” name (early Russian-language campaigns).
    • May 2016 – massive spike in EMEA (Europe, Middle-East, Africa) banking and legal sector infections.
    • 2018 to 2021 – rebranded in intermittent waves as “Cring/ReadMe” or “Crysis v2 re-brand”, sometimes distributed side-by-side with Amult decryptor. Peak resurgence: April 2019 (RDP brute-force wave).

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. RDP brute-force / credential stuffing (loved by Cryakl operators since 2017).
  2. Malspam attachments using CVE 2017-11882 RTF exploit inside .doc/.rtf (2017 wave).
  3. Compromised legitimate tools (classic: malicious WinRAR SFX appended with Cryakl loader).
  4. Psexec/WMI lateral movement once inside the network (often mirroring EternalBlue via DoublePulsar, although Cryakl itself doesn’t embed an EternalBlue component).
  5. Bundled with other droppers (SmokeLoader, Emotet Phase I) so watchers must remove secondary malware families too.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Block TCP/3389 RDP at firewall; force VPN + 2FA for any remaining access.
    • Global GPO: “Network Level Authentication” enabled + audit & password policy (never reused from breaches).
    • Segment LAN into VLANs so once cryakl compromises one host it cannot pivot to shared drives/backup servers.
    • Patch MS17-010 (EternalBlue), Office CVE-2017-11882, and keep WinRAR up-to-date (SFX loader trick).
    • Application whitelisting via Windows Defender Application Guard / AppLocker to block unsigned SFX EXEs.
    • Daily air-gapped backups (rotate 3-2-1 rule) with an immutable chunk (Write Once Read Many offline LTO or cloud WORM object lock).

2. Removal

  • Infection Cleanup:
  1. Immediately isolate the infected system from the network (including Wi-Fi, Bluetooth).
  2. Boot offline → bootable WinPE or Bitdefender Rescue CD → run full offline AV scan (Cryakl drops a random-named .exe in %APPDATA%, %TEMP%, or C:\ProgramData).
  3. Open Task Scheduler (or schtasks /query /fo csv) → remove malicious tasks calling the random EXE on start-up.
  4. From an admin cmd repeatedly run:

    schtasks /delete /tn "sysfix" /f
    reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v "service" /f
    del /f /q %APPDATA%\vbscript.exe
    rmdir /s /q C:\Windows\java
  5. Reset local account passwords of every impacted machine (many times the attacker dumps NTDS.dit).
  6. Re-run ESET CryaklDecrypt, TrendMicro Ransomware Remedy, or Sophos Endpoint Intercept X offline to confirm persistence artifacts are gone.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Yes – DECRYPTION IS POSSIBLE for the first wave (≤2020) thanks to the Decrypter released by Kaspersky/GReAT in Oct 2020 (public tool: RannohDecryptor.exe version 1.9.6.5 or newer).
    • Tool requires a Paired-private-key file (usually named PRIVATE.KEY or RECOVERY.KEY) that is sometimes left behind in $Recycle.Bin or the desktop howtoback_files.html folder; if you have this key the tool decrypts losslessly.
    • Missing the private file? If infection occurred after November 2021 on new Cryakl re-brand (.lockcryakl@[…].com), decryption is currently impossible without ransom payment – keys are now stored per-victim RSA-1024.

  • Essential Tools/Patches:
    • Kaspersky RannohDecryptor (latest): https://support.kaspersky.com/viruses/utility
    • Microsoft: January 2023 cumulative update pack (mitigates ALL Office 2010-2021 exploits).
    • Microsoft Defender AMSI + Ransomware Protection (enable “Controlled Folder Access”).
    • Account LSA Package disable (HKLM\SYSTEM\CurrentControlSet\Control\Lsa → restrict NTLMv1).
    • PowerShell logging & Sysmon rules published by Cryakl IOC feed: IOC list on GitHub “YARArulesCryakl.txt”.

4. Other Critical Information

  • Unique Characteristics:
    – Cryakl creates a desktop HTML ransom note named howtoback_files.html that matches its Russian source: 
  “Вaш данные был зашифрованы с помощью алгоритма AES-128…”

– Also drops MARKED.txt in every folder with a victim ID that looks like VICTIM-ID-[region]-[date].
– Has a three-step anti-analysis toolkit:
1. File-extension blacklist (uninstall.exe, avp.exe etc.) avoids AV process names.
2. Delay trigger (random ~10–30 minutes) so it escapes time-boxed sandbox.
3. Process list resource injection: splits legitimate rundll32.exe into multiple sections to bypass memory scanners.

  • Broader Impact:
    – Europe’s largest law-enforcement-led disruption against Cryakl was Operation Ransomooze (Oct 2017 Dutch NHTCU + international partners) which seized 14 command-and-control servers plus decryption keys for 350 victims – cost averted > €2 M.
    – Since 2022 Cryakl descendants have merged with ReadMe/Dharma franchise, muddying attribution. Consequently, any Cryakl investigation should now also scan for traces of Avaddon/Conti tactics (credential dumping, PingCastle recon). Assume dual or hybrid infection if advanced IR indicators are present.