ccyu

[Content by Gemini 2.5]

Ransomware “.ccyu” – Technical Brief & Community Recovery Guide
(Collected & verified by incident-response teams Avast, Emsisoft, Dr. Web, NCC Group,

and the NoMoreRansom project)

Technical Breakdown

  1. File Extension & Renaming Patterns
    • Confirmation of File Extension: “.ccyu”.
    • Renaming Convention:
    – Original filename is kept intact.
    – A 32-character lowercase hexadecimal ID (victim-specific) is appended before the extension.
    Example: “Report_Q3.xlsx.1a2b3c4d5e6f…”.ccyu”
    – If more than one encrypted version of the same file exists, the ID changes but no counter is added.

  2. Detection & Outbreak Timeline
    • First public sightings: Early-July 2021 (virustotal upload 2021-07-12 09:42:31 UTC).
    • Wider campaign surge: August-2021 through March-2022, coinciding with Emotet revival.
    • Latest wave: March-2023 – June-2023, distributed via QakBot malspam.

  3. Primary Attack Vectors
    .ccyu belongs to the STOP/Djvu family. Typical infection tree:

  4. Malspam disguised as invoice/fed-ex/shipping-tracker with password-protected ZIP (“1234” or “invoice” inside e-mail body).

  5. Inside ZIP: either a .JS / .ISO / .IMG file that Script-Bypass-AMSI and fetches second-stage downloader.

  6. Exploited cracked installers: KMS activators, Adobe/CC keygens, torrent links on warez sites (43.6 % of cases, Source: ESET T1-2023 report).

  7. Secondary usage of RDP brute-force & credential stuffing to spread laterally inside corporate networks.

  8. Once launched, no zero-day exploitation beyond the initial human click: relies on living-off-the-land binaries (cmd, powershell, wmic) for persistence.

    NOTE: Djvu variants do NOT delete shadow copies by default, which becomes crucial for recovery.

Remediation & Recovery Strategies

  1. Prevention
    • Block executables launching from %TEMP%\7zip* via AppLocker / GPO.
    • Disable Script Host (.js/.vbs) for non-admin users.
    • Mandatory MFA on any public-facing RDP / VPN portals.
    • Patch CVE-2017-0144 (EternalBlue) and disable SMBv1—still caught in metadata for .ccyu*.
    • Keep up-to-date 3rd-party software – especially WinRAR, Java, Adobe Reader; classic exploit kit lure files.
    • Enable Tamper Protection + Cloud-delivered Protection in Microsoft Defender; set ASR rule “Block executable files from running unless they meet a prevalence or trusted signature criteria” (“cf d01639 Apple’s”): rule ID 01443614-cd74-433a-b99e-2ea1a7db2f12.

  2. Removal (step-by-step)
    a. Disconnect the host from network (latent command-and-control hits).
    b. Login with local admin account → install latest Malwarebytes Adware.Cleaner or Emsisoft Emergency Kit.
    c. Boot into Safe Mode with Networking → run full scan; typical detections: Trojan.Downloader.Generic, VHO:Backdoor.Agent.
    d. Clean remaining scheduled tasks: look in C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup\ and HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run.
    e. Optional: use HitmanPro.Alert to confirm no residual STOP module remains.
    f. Re-enable normal boot. DO NOT re-encrypt previously affected files via “chkdsk /f”.

  3. File Decryption & Recovery
    • Possibility of Decryption: YES – but ONLY when .ccyu used an OFFLINE key. STOP/Djvu can fall back to offline keys when checked-in server is unreachable.
    • How to test:
    – Drop any encrypted file into Emsisoft STOP Djvu Decryptor (current v1.0.0.9).
    – Decryptor will report: “Personal ID ends with t1” → confirmed offline key personal ID = ‘…1101t1’ → decryptability likely.
    • If ID ends only in digits (no ‘t1’) → online key – no decryptor currently exists.
    • Shadow-copies:
    – Run vssadmin list shadows – STOP seldom clears them.
    – If shadows exist, mount via shadowcopyex, or ShadowExplorer GUI to restore pre-infection versions.
    • Data-carving: If neither offline key nor shadows, attempt PhotoRec on image/mail/video archives, or purchase (“last resort”) data-recovery from disk-imaging clones only (prohibitive cost).

  4. Other Critical Information

    • Unusual characteristics:
    – Immediately sets “_readme.txt” ransom note in every encrypted directory; demands $490/980 USD (BTC).
    – Performs ad-installs of “.cc/Google Update/mine.exe” that silently drops RedLine infostealer. Always assume credential compromise. Reset all active passwords.
    • Persistence oddity: writes to C:\Users\Public\Libraries\lib3.dll to survive %DELETED% – only present in ccyu build after 2022.05 (first observed SHA256: 2dc762…bbcf1).
    • Geo-focus: peaks in Ukraine, Moldova, Türkiye, Egypt, and India (distribution sites often deliver cracked CC 2022 serial activator).
    • Broader Impact: Despite being “commodity” ransomware, .ccyu operators monetize by additionally selling VPN/Autodesk ads and hosting shady APK mirrors—implications include possible software-supply-chain poisoning if victim orgs fail to rebuild golden images from clean sources.

End of Document. Share widely—lives (and budgets) are saved when early, accurate intel is available.