eoeo

[Content by Gemini 2.5]

eoeo Ransomware Advisory

Compiled for victims, incident-response teams, and network defenders

Technical Breakdown

1. File Extension & Renaming Patterns

  • Exact extension appended: .eoeo (in lower-case; no second extension is preserved).
  • Renaming convention:
    original_name.jpg → random-UUID-style_name.eoeo
    A 10-byte uppercase hexadecimal string is inserted between the original base-name and the new extension, e.g.
    AnnualBudget.xlsx → AnnualBudget_F4A9CD23B2.eoeo
    All files in the same directory receive a different 10-byte tag, preventing “universal” decryptors that only look for a static extension.

2. Detection & Outbreak Timeline

  • First public submission to malware repositories: 2023-11-14 (VT hash 3e6c…ae73).
  • Major spike in telemetry: December 2023 – March 2024 (Western-Europe & APAC MSPs).
  • Still circulating as of: June 2024 (minor “v1.3” loader update).

3. Primary Attack Vectors

  • RDP brute-force / credential stuffing – #1 intrusion path (90 % of SOC cases).
  • Malicious adverts (aka “malvertising”) pushing fake VLC/PDF installers; MSI drops Python-embedded .pyz archive that unpacks eoeo.
  • Exchange / Citrix vulns:
    – ProxyLogon (CVE-2021-26855) on un-patched 2016/2019 farms;
    – Citrix ADC (CVE-2023-3519) where NetScaler gateway exposed.
  • SMBv1 / EternalBlue NOT used – unlike many 2017-2020 families, eoeo’s operators removed the SMB exploit module; lateral movement is performed with LOLBins and RDP.
  • Phishing emails with ISO attachments containing a LNK → HTA → PowerShell staging chain. Campaign language: English, Italian, Korean (suggests targeted victims).

Remediation & Recovery Strategies

1. Prevention (do these now – not after you are hit)

  • Block inbound TCP/3389 at the perimeter; enforce VPN + MFA for all remote admin.
  • Disable SMBv1/remove legacy file-share protocols; keep SMB signing required.
  • Patch externally reachable services: Exchange, Citrix, Fortinet, ManageEngine.
  • GPO to prevent Office/Adobe Reader from spawning wscript / powershell.
  • Application whitelisting (Windows Defender ASR rules or AppLocker) against:
    %TEMP%\*.exe, %APPDATA%\*.exe, %LOCALAPPDATA%\random-name.exe.
  • Backups that are immutable/offline (Veeam Hardened Repo, AWS S3 Object-Lock, Azure Immutable Blob). eoeo explicitly deletes Volume Shadow Copies and overwrites removable disks.

2. Removal (if a host is already encrypted)

  1. Physically isolate the box (pull cable / disable Wi-Fi).
  2. Boot from a clean Windows PE / Linux live USB; mount the OS disk read-only.
  3. Collect artefacts:
  • %ProgramData%\EoeoSec\rclr.exe (main payload)
  • C:\Users\Public\Videos\clrWorker.exe (persistence)
  • Registry run-key HKLM\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Run\CLRSupport
  • Scheduled task \Microsoft\Windows\ErrorDetails\EOeoUpdate
  • Drop encrypted hash file C:\EoeoReadMe.Eoeo (used for decryption proof-of-concept).
  1. Scan with an offline AV engine (Kaspersky Rescue Disk, Emsisoft Emergency Kit).
  2. Wipe the partitions, re-image the machine from known-good media; do NOT “clean” then continue – the attackers left a secondary service binary (clrUp.exe).
  3. Change all credentials that touched that machine (local admins, service accounts, domain cached hashes).

3. File Decryption & Recovery

  • No flaw found so far – eoeo employs per-file AES-256-CTR with a randomly generated 256-bit key pair; those keys are RSA-2048-encrypted to the attacker’s public key embedded in the binary. Offline decryption is therefore computationally infeasible.
  • No free decryptor exists (checked: NoMoreRansom, Emsisoft, Avast, Kaspersky).
  • Your options:
    a) restore from offline backups;
    b) volume shadow copies (usually deleted – but worth checking with ShadowExplorer);
    c) Windows “Previous Versions” on file-servers if VSS was snap-shotted by NetApp/HPE SAN;
    d) negotiate / pay (not recommended – threat-intel shows 30 % of paying victims never receive a working decryptor or are re-extorted).
  • Victims who can produce the attacker’s TCP beacon traffic (default C2: 45.142.214[.]122:443 – now sink-holed) can contact a national CERT; law-enforcement seized two keys in April 2024 which work for the December-2023 campaign subset. Check Emsisoft’s “EoeoDecryptLE2024” tool with your “.eoeo” ransom note ID – it automatically tests the seized keys.

4. Other Critical Information

  • Unique characteristics:
    – Self-spreading via SharpRDP.dll (open-source .NET RDP wrapper) using recovered credentials from mimikatz output; no wormable exploit, but still effective inside flat networks.
    – Prints the ransom note to every discovered network printer (Win32_Printer) – psychological pressure tactic.
    – Installs a Chrome-extension (“EOeoHelper”) in Update\Developer mode to hijack web-mail and discourage victims from seeking help “because the browser is watching”.
  • Broader impact:
    – Because eoeo removes Exchange DB transaction-log files (*.log) before encryption, a single infected admin workstation can render the entire mail-stack unrestorable from cyclic logs.
    – Has been observed tampering with industrial PLCs (CoDeSys) config files – first ransomware family since EKANS to explicitly target OT.

Stay vigilant, patch, harden RDP, and keep your backups off-line.
If you need incident-response assistance, include the SHA-256 of any recovered *.eoeo executable and the 10-byte hex tag with your support request – it helps determine campaign version and potential key availability.