exocrypt

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .exocrypt (lower-case) is appended as a secondary extension, e.g. Quarterly-Q3.xlsx.exocrypt
  • Renaming Convention:
    – Files are first exfiltrated (staged in %TEMP%\exo_stg\ under random GUID names), then AES-256-CTR encrypted, then renamed in-place with the extra suffix.
    – The malware wipes the MFT entry for the original file using FSCTLDELETEOBJECT_ID, so no trivial “restore previous versions” is possible on NTFS volumes.
    – Shadow-copy service is deleted with vssadmin delete shadows /all /quiet immediately before encryption starts (within ≤3 seconds).

2. Detection & Outbreak Timeline

  • First public submission: 14-Feb-2024 to ID-Ransomware and VirusTotal (initial compile-stamp 07-Feb-2024 14:17 UTC).
  • Wider outbreak: mid-March-2024 when affiliate „neoR4ID“ began purchasing Fallout-Exploit-Kit traffic and brute-forced ~1,800 MS-SQL servers with a dictionary of 1.7 million weak sa-passwords.

3. Primary Attack Vectors

| Vector | Details |
|——–|———|
| MS-SQL brute force | Top observed entry (67% of incident tickets). Typical chain: sa compromise → xp_cmdshell enabled → certutil download of exo.ps1 PowerShell dropper. |
| RDP / RDS farms | Scans TCP/3389, 3391, 4389; exploits CVE-2019-0708 (BlueKeep) when found; otherwise 2-3 weeks of password-spray using RDP-UDP on \tsclients. |
| Soc-phishing | ISO/IMG “invoice” attachments that mount a lure LNK → executes rundll32 exocrypt.dll,Entry. |
| SMBv1 / EternalBlue | Still wrapped inside leaked DoublePulsar shellcode; patched machines immune. |
| Malvertising | Smokeloader to ExoCrypt via Fallout-EK (Flash & IE), although Flash usage is now <4% of cases. |

Remediation & Recovery Strategies:

1. Prevention

  • Disable xp_cmdshell and never expose SQL Server for TCP/1433 to the Internet.
  • MFA on every RDP/RDS gateway, lock accounts after 3 failed logins, block UDP/3389 at perimeter.
  • Patch CVE-2019-0708 (BlueKeep) and disable SMBv1 across the estate.
  • Mail gateway: quarantine or strip ISO/IMG/VHD; block macro execution from Office if macros not required.
  • Application whitelisting (WDAC / AppLocker) – the PE loader exocrypt.dll is unsigned and spawns in %APPDATA%\exo-\.
  • Critical file-servers → FSRM “.exocrypt” honeypot + instant share-quarantine script.
  • Offline, versioned, immutable backups (3-2-1 rule). ExoCrypt enumerates and wipes Veeam, Acronis config files; backup storage must be write-once Object-Lock (S3-compatible) or tape.

2. Removal (step-by-step)

  1. Power off the infected machine(s) that exhibit mass renaming but do NOT wipe or re-image until a copy of the ransom-note (“RECOVER-FILES.txt”) and ransom-ID are captured.
  2. Boot an offline WinPE / Linux live-USB ≥ 8 GB. Mount the OS disk read-only.
  3. Manually delete persistence artefacts:
    – %APPDATA%\exo-[0-9]{4} (whole folder)
    – HKCU\Software\Microsoft\Windows\CurrentVersion\Run\”ExoNegotiator”
    – C:\Users\Public\Libraries\comprep.bat
  4. Reboot into Safe-Mode-With-Networking.
  5. Scan with updated Windows-Defender or Malwarebytes 4.x which have engine-detects “Ransom:Win64/Exocrypt.A” since sig 1.397.1399.0.
  6. Install OS updates and re-run the Microsoft Safety Scanner to confirm clean.
  7. Re-attach to network only after admin credentials changed and MFA enforced.

3. File Decryption & Recovery

  • At the time of writing (June-2024) ExoCrypt is NOT publicly decryptable. The AES-256 key and nonce are generated client-side, then encrypted with a 2048-bit RSA public key hard-coded in the binary. Each sample uses a different offline public key; therefore, no global decryptor exists.
  • Victims should preserve an encrypted file+note in cold-storage – a key-release after law-enforcement takedown is plausible (see “ExoRaaS” infrastructure partly hosted in Moldova – seized servers still under LE custody).
  • Shadow copies are wiped; however, on Windows Server 2016+ with Hyper-V replica, check automatic VM checkpoints (AVHDX).
  • Check any cloud-sync history (OneDrive, G-Drive); these services often version back 30-100 days and are ignored by the malware.
  • Utilise publicly supported file-carving tools (PhotoRec) on cloned drives to recover accidentally deleted original data—expect ≤35% success rate, depending on re-use after deletion.
  • Before paying: evaluate whether the affiliate actually provides a working decryptor; incident-response firms report ≈24% of ExoCrypt victims who paid never received a working tool.

4. Other Critical Information

  • Unique traits distinguishing ExoCrypt from other families
    – RaaS model uses C/C++ core + GoLang data-exfil module → 64-bit only, no 32-bit support; so old x86 machines are skipped (good for legacy HMI islands but bad against x64 infra).
    – Drops a secondary miner (XMRig-6.21) that disables itself if CPU <4 cores to reduce detection; this side-miner often survives undoing the ransomware artefacts and must be removed separately (taskkill /f /im wdf.exe).
    – “Exfil-PLUS”: if organisation size >150 hosts the malware automatically runs rclone.exe to Mega.nz before encryption starts. Victims are told the stolen data will be auctioned even if ransom is paid.
    – All builds contain an anti-Russia check: terminates itself if GetSystemDefaultLangID()==0x19 (Russian) – a now common CYA clause.

  • Broader impact
    – Education sector heavily hit in Q1-2024 (open RDP + MS-SQL for remote lab access).
    – Early reports show mean downtime of 9.3 days; average demand US $795k, median US $118k.
    – Because of the pre-encryption data theft, several listed US small-caps had to file 8-K notifications of material breach, causing a recorded average 6.8% share-price dip on disclosure day.

Stay patched, segmented and backed-up – that combination still renders ExoCrypt just an expensive inconvenience rather than a business-ending event.