EXOCRYPT-XTC Ransomware – Community Threat Guide

(File extension observed: .xtc)

1 – Technical Breakdown

1.1 File Extension & Renaming Pattern

Confirmed extension appended: .xtc
Example: Quarterly-Report.xlsx → Quarterly-Report.xlsx.xtc
No email, victim-ID, or random hex string inserted – the malware keeps the original base name and simply tacks on “.xtc”.
Ransom note dropped in every affected folder: README_TO_RESTORE_XTC.txt (generic name; may vary slightly in recent builds).

1.2 Detection & Outbreak Timeline

First public hunting-rule hits: late-October 2023 (uploads to VirusTotal from US & DE victims).
Notable spikes:
– Nov 2023: SMB-facing healthcare servers (ESXi+Windows dual campaigns).
– Jan-Feb 2024: exposed RDP + MSSQL brute-forces targeting MSPs in LATAM.
Top AV signatures: Ransom.Exocrypt, Trojan-Ransom.Win32.XTC.*, RansomXTC-A.

1.3 Primary Attack Vectors

EternalBlue / SMBv1 – still weaponised because many small networks have not disabled SMBv1; spreads laterally once a single host is breached.
Brute-forced or stolen RDP / VNC credentials – attacks on TCP-3389, 5900; explicit logon events (ID 4624, type 10) followed by xtc-ransom.exe dropped in %ProgramData%.
Phishing with double-extension ISO or ZIP → LNK → PowerShell loader – the final payload is retrieved from https://files-anonymous[.]top/xtc/x64.bin (URL rotated weekly).
Weaponised flaws in public-facing apps – observed exploitation of:
– PaperCut NG/MF CVE-2023-27350 (Mar-Apr 2024)
– MovableType 7 CVE-2023-39361 (only a handful of cases, but proves Linux variants exist).
Living-off-the-land: Uses nltest /dclist, net view, PsExec.exe (redist version) to self-propagate; terminates 92 security / backup processes by hash list before encryption.

Encryption engine: ChaCha20 + RSA-2048 (public key embedded). Volume shadow copies deleted via vssadmin delete shadows /all; Windows backup catalog wiped; ESXi /vmfs/volumes halted with esxcli vm process kill.

2 – Remediation & Recovery Strategies

2.1 Prevention (apply BEFORE any incident)

Disable SMBv1 at domain/DC level (GPO: Computer > Policies > Admin Templates > MS Security Guide > Disable SMB1).
Segregate VLANs; place critical servers behind jump hosts; enforce MFA on ANY remote-desktop or SQL endpoint.
Harden RDP: set NLA + account lockout (5/30 min), move to non-default port, and use RDP-Gateway + MFA.
Patch aggressively: PaperCut, MovablType, ESXi, Fortinet, ConnectWise – every campaign variant so far has used n-day, not 0-day, flaws.
Application allow-listing / WDAC. Hash of primary dropper up to 24 Apr 2024:
– 8bda6b1fd2cf9a71c4cb9189bc5ec6a9 (MD5) – block.
Backups: at least one daily offline (tape or immutable cloud), plus quarterly restore drill; backup solutions must require MFA for retention-policy change.

2.2 Removal / Incident Handling (step-by-step short checklist)

Disconnect NIC / shut off Wi-Fi—power-off is a last resort; live-response preferred.
Collect triage: MFT, AmCache, SRUM, EVTX, RAM dump (use Kape or Velociraptor).
Boot an offline AV/EDR scanner (Windows PE + Defender or ESET SysRescue) – delete the ransom binaries listed in next bullet.
Typical files (paths randomised by affiliate; look for same hash):
– %ProgramData%\xhelp.exe
– %TEMP%\svcss.exe
– %AppData%\Microsoft\Windows\psexec.exe
Run del /f /q after hash verification inside WinRE to avoid reinfection.
Reset all local admin & service account passwords from a clean DC; revoke any new local users (names “backup”, “svc”, “wusa”).
Review GPO / scheduled tasks – removes any RunOnce entries invoking README_TO_RESTORE_XTC.txt or PowerShell stagers.
Patch & re-image any machine that was encrypted (forensic image first if regulators require).
Only after a 24-hour passive monitoring period (network taps, EDR telemetry clean) reconnect to production VLAN.

2.3 File Decryption & Recovery Options

CURRENT STATUS: No free decryptor as of 24 Apr 2024. Key pair is uniquely generated per victim, private key never leaves C2.
Options:
a) Restore from OFFLINE backup (fastest, safest).
b) Negotiation is technically possible but strongly discouraged—payments fuel the ecosystem and there is no guarantee; 2023 victims reported 35% non-delivery rate.
c) Shadow-explorer hunt: sometimes fails because VSS is purged, but if you have SAN-level snapshot (NetApp, Pure, etc.) map and copy before removal script runs.
d) Partial recovery artefacts: For Office documents only, try Office “Open & Repair” – XTC encrypts in 1 MB chunks; files < 1 MB are 100% encrypted and therefore unreadable, larger ones may recover headers.
If a universal decryptor is ever released, the #NoMoreRansom project will host it; subscribe to RSS feed www.nomoreransom.org/en/rss-index.html.

2.4 Other Critical Information & Wider Impact

Distinctive lateral-movement marker: makes a WMI class root\default:XTC_PING and stores campaign ID & bitcoin wallet in it—look for it when hunting.
ESXi / Linux variant extensions: .xtc (same) but note name in ransom note is _README_TO_RESTORE_XTC.txt__ (double underscore) – helps distinguish VMware-only hit from Windows hit.
Extortion model: data-theft + encryption (double extortion). Data leaks posted at 6i5ytw5ey3t6oqygfrs6k665axc3t6cs3rvoolcpskdtvwf3jyge4mad.onion (currently offline) when victim refuses to pay within 7 days.
Community-contributed IOC Yara (short):

  rule Windows_Ransom_XTC_Apr2024 {
      meta:
          author = "community"
          description = "Detects PE builds of Exocrypt-XTC (cha-cha key schedule)"
      strings:
          $rsa="-----BEGIN PUBLIC KEY-----"
          $cha="expand 32-byte k"
          $xtc="XTC_PING"
      condition:
          all of them
  }

Run across memory dumps and pagefile.sys during DFIR; fires even if sample is packed.

Regulatory fall-out: Because health-care orgs were early targets in the US, HHS OCR issued a sector alert (Dec 2023); breach notifications now hitting 60-day timer and risk category “Cyber-Extortion”.

Bottom Line

.xtc = Exocrypt-XTC – ransom note README_TO_RESTORE_XTC.txt.
No publicly working decryptor – recovery hinges on immutable backups.
Kill-chains merge old tricks (SMBv1, brute RDP) with new CVE n-days—patch, MFA, segment, and keep at least one daily offline backup.

Stay safe, share IOCs, and never run unknown .exe attachments. If you uncover new decryptor news or fresh hashes, feed them back to the #NoMoreRansom project so we can update this guide for everyone.

exocrypt xtc