ehiz

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .ehiz
  • Renaming Convention: Each affected file is appended with a second extension in lower-case → .ehiz
    Example:
    annual_report.xlsx → annual_report.xlsx.ehiz
    No e-mail, ID string, or random prefix is added—only the new extension.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First submissions to public sandboxes and incident-response forums appeared in late August 2023. Wave of infections continued through Q4-2023 and remains visibly active in 2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    – Malicious e-mail attachments (fake invoices, job offers, and “payment advice” PDFs with embedded .js or .iso).
    – Exploitation of exposed or brute-forced RDP / AnyDesk / TeamViewer sessions—once inside, attacker drops ehiz manually.
    – Software cracks & keygens on warez/torrent sites (WinRAR, Adobe, Ableton, KMS-pico, etc.).
    – Secondary payload to existing TrickBot/RedLine Stealer infestations.
    – No indication (so far) of worm-like behaviour or SMB-based exploit (EternalBlue, etc.).

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    – Disable Office macros by policy; treat .js, .vbs, .hta, and .iso coming from outside as high-risk.
    – Harden RDP: enforce NLA, lock-out after 3–5 failed logins, white-list source IPs, move to 3389/rdp-gateway + MFA.
    – Keep Windows, Office, and AV/EDR signatures fully patched (ehiz has been seen bypassing older Defender builds).
    – Use application whitelisting (AppLocker / WDAC) to block %TEMP%\random-name.exe execution.
    – Network segmentation + offline/off-site backups tested weekly (3-2-1 rule).
    – Restrict user write permissions to mapped shares whenever possible.

2. Removal

  1. Disconnect machine(s) from network (Wi-Fi & Ethernet).
  2. Boot into Safe Mode with Networking or use a clean WinPE/Windows-RE USB.
  3. Delete the persistence registry value typically placed at
    HKCU\Software\Microsoft\Windows\CurrentVersion\Run → SysHelper = %AppData%\syshelper.exe (name may vary).
  4. Remove the dropped executable (common locations):
    %AppData%\syshelper.exe
    %UserProfile%\recent\<random>\<random>.exe
    C:\Perflogs\<random>\<random>.exe
  5. Delete accompanying scheduled task (“ServiceInstall” / “BackupSync”).
  6. Wipe shadow copies only after ensuring clean backups are available).
  7. Update AV engine; run a full scan or preferred remediation tool (see section 4) to sweep secondary loaders.
  8. Reboot; re-scan before reconnecting to LAN.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – .ehiz is part of the STOP/Djvu family, 2023+ variants. Encryption is secure (Salsa20 + RSA-2048 offline key set).
    – If the sample used the OFFLINE key (commonly observed) a free decryptor released by Emsisoft will restore files:
    https://www.emsisoft.com/ransomware-decryption-tools/stop-djvu
    – If an ONLINE key (unique per victim) was used, the public decryptor will NOT work; only the criminals possess the private RSA key.
    – Check by feeding any tiniest encrypted file + original into the Emsisoft decryptor—tool will report key availability.
    – Data-recovery without a key: rely on clean backups, Windows shadow copies (often deleted), or file-carving tools (PhotoRec) only for non-fragmented files that existed pre-encryption.

  • Essential Tools/Patches:
    – Latest Windows cumulative update (Defender engine ≥ 1.391.x detects as Ransom:Win32/StopCrypt).
    – Emsisoft STOP/Djvu Decryptor v1.0.0.4+.
    – Malwarebytes ADWCleaner / ESET Online Scanner for follow-up cleanup.
    – Microsoft’s Sysinternals Autoruns + Process Explorer for manual inspection.
    – “ShadowExplorer” (freeware) for quicker shadow-copy restore if VSS survived.

4. Other Critical Information

  • Additional Precautions:
    – Ransom note filename is _readme.txt (identical to other STOP/Djvu strains) and asks for $499–$999 paid in BTC.
    – Contact e-mails vary (    [email protected],[email protected]`, etc.).
    – The malware also drops several information-stealer modules (RedLine) before encryption—assume passwords, browser data, and crypto-wallets are compromised; rotate all credentials post-recovery.
    – Signing certificate revoked quickly, so binary hash is different in every campaign: rely on behaviour rather than hash block-listing.

  • Broader Impact:
    – STOP/Djvu currently accounts for >70% of ransomware submissions to ID-Ransomware; .ehiz is one of >600 extensions used since 2018.
    – Home users paying the ransom frequently receive no key or a non-functional one—law-enforcement & AV vendors therefore discourage payment.
    – Criminal group’s toolchain overlaps with data-theft, leading to double-extortion in separate cases (RedLine exfil first, then .ehiz encryption), so treat incidents as both ransomware + data-breach.

Stay sceptical of “miracle” unlock offers, patch aggressively, keep offline backups, and verify decryption feasibility with the free Emsisoft utility before considering any ransom payment.