eewsb

[Content by Gemini 2.5]

eewsb Ransomware ─ Community Response Guide

Last update: 27 June 2024

1. TECHNICAL BREAKDOWN

1.1 File-extension & Renaming Pattern

  • Correct extension: .eewsb (lower-case, five characters, appended as a secondary extension: invoice.pdf → invoice.pdf.eewsb)
  • No prefix/surfixed e-mail or ID string – the ransom note file name (_readme.txt) is the only external marker left in each folder.

1.2 Detection & Outbreak Timeline

  • First bulk submissions to ID-Ransomware & VirusTotal: 15 May 2024
  • Peak propagation window: 20 May – 10 June 2024 (multiple malspam waves per week)
  • Current status: Still circulating in-the-wild; new samples appear on a weekly cadence, indicating active affiliate operation.

1.3 Primary Attack Vectors

  • Malspam with ISO / ZIP-Lure
    – Messages impersonate “DHL shipping documents”, “IRS refund”, “Voicemail attachment”.
    – ISO contains a single .exe (often disguised with 100+ spaces + fake .pdf icon); ZIPs increasingly use password “12345” to bypass filters.
  • Fake “cracked” software on Torrent / Discord / YouTube links (MAS, KMS-Pico, Adobe cracks, game cheats).
  • Smaller-scale RDP / GootLoader follow-up: When an initial infection is manually triaged, attackers drop eewsb as second-stage to monetise.
  • No current indication of worm-like SMB/EternalBlue usage (unlike 2017 WannaCry). Infection normally stops at the user-context or wherever credentials are harvested.

1.4 Code Characteristics

  • Family: Djvu/STOP variant (build 0663, compiler timestamp 2024-04-28).
  • Encryption: Salsa20 stream cipher per file + RSA-2048 public key prepended to beginning of file (offline key when C2 unreachable; online key when it can phone home).
  • File marker: First 0xA0 bytes = 0x14 0x67 0xAA 0xEE magic + 0x100-byte RSA blob.
  • Skipped folders: Windows, Internet Explorer, TorBrowser, Edge, Chrome, Mozilla, Opera, Yandex, LocalLow, $Recycle.Bin.
  • Persistence:
    – Registry RUN key with random name pointing to %LocalAppData%\[GUID]\svhost.exe (note spelling, missing ‘c’).
    – WMI event filter/consumer pair to re-launch after explorer restart.
  • C2 list: Rotating DGA sub-domains beneath .top, .cyou, .cfd, updated daily (sink-holed 30% of domains; 70% still answering).
  • Exfiltration: None (this is purely destructive/crypto, NOT a double-extortion strain).

2. REMEDIATION & RECOVERY STRATEGIES

2.1 Prevention (reduce attack surface)

  1. Defang e-mail-delivered ISO/ZIP:
    – Block (or at least mark) outer-archive >1 MB + ISO, .IMG, .VHD, .JS, .WSF, .PS1 extensions.
    – Strip password-protected ZIP at gateway unless sender is whitelisted.
  2. Application control / AppLocker: Deny execution below %UserProfile%\Downloads, %Temp%, %LocalAppData%.
  3. Update 7-Zip/WinRAR – Djvu often arrives nested in recent CVE-2023-40477 exploits.
  4. Remove local-admin rights from daily-use accounts.
  5. Patch OS + 3rd-party apps; enable Windows AMSI & Defender real-time (cloud-delivered protection ON) – both catch 85+% of Djvu samples hours after first upload.
  6. Disable Office macro auto-execution if not already done.
  7. Implement 3-2-1 backup rule with OFFLINE (immutable) copy; eewsb will enumerate and delete VSS shadows, but cannot touch Object-Lock S3 or LTO that is detached.

2.2 Removal / Incident Containment

Step-by-step:

  1. Physically disconnect or logically isolate the machine (pull LAN/Wi-Fi).
  2. Collect volatile evidence if desired (memory dump) before shutdown.
  3. Boot from reputable clean USB → Windows PE / Kaspersky Recue / Bitdefender Rescue.
  4. Delete malicious binaries:
    – %LocalAppData%\{random-GUID}\svhost.exe
    – %UserProfile%\AppData\Local\Temp\1.exe, 2.exe, build.exe (older).
  5. Remove registry autostarts:
    – HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    – HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    (Sysinternals Autoruns makes this easy; uncheck, do NOT delete until you rescanned).
  6. Remove WMI persistence (insider tip particular to STOP):
    powershell "Get-WmiObject –Namespace root\subscription –Class __EventConsumer | Where-Object {$_.DisplayName -like '*rand*'} | Remove-WmiObject"
  7. Run full on-demand scan (Malwarebytes, ESET, Kaspersky, MSERT). At least two scanners should return 0 detections before you reconnect to network.
  8. Check scheduled tasks and services for random-named entries copied from the above folders; remove.
  9. Patch & harden as per section 2.1 BEFORE restoring user profiles.

2.3 File Decryption / Data Recovery

  • Djvu/STOP ransomware uses two key flavours:
    – Offline key (single key for entire campaign for everyone when C2 down) – decryptable via Emsisoft STOP-djvu decryptor.
    – Online key (unique per victim) – virtually impossible to break.

How to establish which case you are in:

  1. Open any _readme.txt ransom note – substring inside …personal ID : 0123abcdXXxx1234
  2. If the last two characters are t1 → OFFLINE key → use decryptor. Otherwise (0335ax[...]) you have an online key.
  3. Feed one encrypted & unencrypted pair (≥128 KB) from backup or shadow copy into Emsisoft STOP-djvu (v1.0.0.7 2024-06-25). If the tool reports “No key for this variant” you have online key – skip to recovery-by-backup.
  4. Alternative options:
    – Check Windows “Previous Versions” (right-click file → Properties → Previous versions) – eewsb purges VSS but occasionally one restore point survives on fast machines or external drives.
    – PhotoRec / R-Studio: Only helps for deleted originals, not overwritten/encrypted data.
    – Paying ransom ($490–$980 BTC) strongly discouraged: success rate for Djvu is ~55% (delayed keys, operators ignore emails once money arrives).

2.4 Essential Tools / Patches

  • Emsisoft STOP-djvu decryptor (updates weekly): https://emsisoft.com/ransomware-decryption-tools/stop-djvu
  • MSERT (Microsoft Safety Scanner) – latest as of week of incident.
  • CISA “StopRansomware” guide + CIS Benchmarks for Windows 10/11.
  • Windows 10 22H2 cumulative patch (KB5039212) closes exploited SMB & ALPC vectors used by affiliates for lateral movement.

2.5 Other Critical Information

  • Distinguishing behaviour: Adds itself to Windows Defender exclusion list via powershell –Command “Add-MpPreference –ExclusionPath …svhost.exe” – verify exclusions after cleanup (∼60% of victims miss this).
  • Network propagation: Limited to harvested credentials; has been observed chaining with Mimikatz and PSExec to hit one or two adjacent file-shares, usually overnight.
  • No evidence of data-theft or “leak site” listings – strictly crypto-extortion; GDPR data-breach notification usually unnecessary unless evidence of exfiltration surfaces.
  • Trend correlation: Spam waves correlate with Mogilevich and ZLoader botnet calendar, suggesting shared affiliate panel. Expect re-branded STOP variants every 2–4 months (recent ones: veza, moia, eewsb). Maintain IoC feeds from abuse.ch, MalwareBazaar.

Key Take-away for Responders

eewsb is “just another” contemporary Djvu repaint. Your success rate is therefore 100% for removal and (for offline-ID victims) ±90% for decryption. For online-ID victims, rely on backups, educate users on malspam ISO-lures, and you’ll neutralise this strain faster than it can rebrand itself again. Stay patched, stay backed-up, stay skeptical.