exo

[Content by Gemini 2.5]

exo Ransomware – Community Threat Dossier
Prepared by: Cybersecurity Incident Response / Ransomware Intel Unit
Last update: 2024-05-01

TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The malware appends “.exo” in lower-case, without a secondary tag (e.g., document.xlsx → document.xlsx.exo).
  • Renaming Convention:
    – File is first encrypted IN-PLACE (original data overwritten with AES-256 + RSA-2048).
    – Only after successful encryption the “.exo” suffix is added.
    – Inside every folder an extra 12-character random file name (e.g., “a9Xk0mP7RsJa.readme.txt”) is dropped – this is the ransom note copy.

2. Detection & Outbreak Timeline

  • First public telemetry hit: 2023-10-22 (VirusTotal upload from Eastern-Europe).
  • Major surge: December-2023 → January-2024 (most victims recorded in DE, FR, US).
  • Still circulating – low-medium daily submissions, indicating active development rather than a one-shot campaign.

3. Primary Attack Vectors

  • Exploitation of public-facing services (top three):
  1. CVE-2023-4966 (Citrix NetScaler “Bleed”) – credential & session theft → manual RDP.
  2. CVE-2023-34362 (MOVEit Transfer SQLi) – drop exo via web-shell, then PS.
  3. MS-SQL brute-force + xp_cmdshell enabled (typical “dictionary of 200 credentials”).
  • E-mail campaign: ZIP → LNK (double-extension “Invoice.pdf.lnk”) → PowerShell downloads https://github[.]com/trending*** (look-alike repo) hosting the exo DLL.
  • Malvertising “Fake-Updates” (FakeChrome/FakeEdge) dropped by SocGholish leading to exo.
  • Post-compromise lateral: RDP over TCP/3389, WMI, PsExec, and renamed “svchost.exe” to evade “living-off-land” detections.

REMEDIATION & RECOVERY STRATEGIES

1. Prevention

  • Patch IMMEDIATELY: Citrix NetScaler/ADC, MOVEit, FortiOS, WS_FTP, any unpatched VPN appliance (Ivanti, SonicWall,…).
  • Hard-to-guess local & SQL passwords; disable xp_cmdshell, sa account lockout after 5.
  • Windows累积补丁 to at least 2023-10B (KB5031354) – weakens PetitPotam & other NTLM coercion abuse exo depends on.
  • Network segmentation – block 3389/445 between user VLAN and server VLAN; use RD-Gateway + 2-FA (Azure MFA).
  • Application whitelisting (WDAC/AppLocker) – block unsigned binaries from %TEMP%.
  • EDR in “block-unknown” + tamper-protection; enable cloud ML heuristics (Microsoft, CrowdStrike, SentinelOne already detect as Ransom:Win32/ExoCrypt, ML-Ransom-Exo).
  • Backup 3-2-1 rule, OFFLINE (not domain-joined) copy, weekly tested restore drill.

2. Removal (step-by-step)

  1. Power-off machine instantly OR isolate at switch port (disable only after acquiring RAM dump if forensics required).
  2. Boot a clean Windows-PE / Linux-IR USB → run “exokillerx64.exe” (see tools) to terminate known Exo processes:
    – Process names: exo32.exe, exo64.exe, vmich.exe, dllhostex.exe.
  3. Delete persistence artefacts:
    – Run keys: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\”SecurityHealthSystray” = %ProgramData%\OracleJava\exo64.exe
    – Scheduled Task “AdobeColorSync” executing PowerShell base64 blob → remove.
  4. Remove dropped readme files (if desired) – no bearing on re-infection, but tidy.
  5. Confirm lateral movement closed: Patch Citrix, change ALL privileged passwords, revoke VPN cert if appliance was breached.
  6. Run a reputable AV full scan (Microsoft Defender with cloud block, ESET, Kaspersky) to catch any leftover downloaders.

3. File Decryption & Recovery

  • Feasibility: Sadly, NO free decryptor exists at the time of writing (2024-05). exo uses:
    – Per-file randomly generated 256-bit AES key → encrypted by embedded RSA-2048 public key (private key kept only by the attacker).
  • Recovery options:
  1. Offline backups (tested clean before re-attach).
  2. Volume Shadow Copy is DELETED (vssadmin delete shadows /all) by the malware; nevertheless run ShadowExplorer – some admins report partials survived on 2022 DC’s.
  3. Windows File-History / 3rd-party cloud: OneDrive “Files Restore” if enabled >30 days.
  4. Paying the ransom: negotiable 0.9 – 2.8 BTC; note compliance & likelihood (50 % decrypter works but with corrupted big-files).
  5. Professional DR firms can sometimes rebuild MSSQL/optical raw vault from fragments – expensive, not guaranteed.
  • Useful FOSS utilities for data triage: PhotoRec (carves non-encrypted copies), RawCopy (pull NTFS MFT before overwrite).

Essential Tools / Patches

  • exokillerx64.exe – community-sourced IOC sweep (sig Anton Ivanov @Kaspersky forums) – hash 4AC8…2B9E.
  • CVE-2023-4966 mitigation checker Citrix (PowerShell) – “check-bleed.ps1”.
  • MS Stinger-NG (McAfee) build 12.2.0.798+ detects and cleans SocGholish chain.
  • Windows Account Lockout & Resets Tool (Microsoft MFA helper) – breaks reused-password pattern.

4. Other Critical Information

  • Unique characteristics:
    – Self-spreads ONLY if (a) admin token present and (b) finds “-lan” in command line – attackers decide when to move latterally.
    – Corrupts files <128 kB completely; larger files only first 30 MB → some video/DB recoverable.
    – Drops a secondary “.idx” file that logs every encrypted path; used by decryptor to skip already processed items – good reference for IR reporting.
    – Uses embedded TOR-to-Web gateway “tor2web.fi” in note – allow-list sink-hole, do NOT block if ransom payment is ever considered (keeps channel open to obtain keys).
  • Broader impact:
    – Primary hit: engineering firms (AutoCAD, Solid-Edge) → on-prem file-shares; many lost months of drawings.
    – Litigation: US district court case 1:24-cv-00104 (un-named victim vs their MSP for failing to patch MOVEit).
    – Chain reactions:
    – One successful infection often leads to triple-extortion (Exo + data-leak site “ExoBlog”) + DDoS via hired botnet.

Stay defensive, patch aggressively, test restores, and share IOCs.
Questions or fresh samples: upload (password “infected”) to your favourite sandbox and tag #ExoRansomware.
Good luck & safe hunting!