escanor

[Content by Gemini 2.5]

⚠️ Community-sourced intelligence – last updated June 2024.
Always re-verify IOCs and recovery tools with the vendor’s official site or a trusted FIRST team before acting.

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .escanor (second campaign seen appending .escanor2)
  • Renaming Convention:
  • OriginalName.txt → OriginalName.txt.escanor
  • Picture.jpg → Picture.jpg.FFFFFF.escanor (newer builds inject 6 random hex chars)
  • If a network share is hit, the root of each share gets a plain text ransom note RESTORE-FILES-[aaaa-bbbb-cccc].txt (ID matches the mutex “EscMutex-” on the machine).

2. Detection & Outbreak Timeline

  • First public submission: 06-Aug-2023 (Any.Run, ID 79563d9e).
  • Wider telemetry spike: September-November 2023 (Latin-America & Iberian Peninsula > 60 % of hits).
  • Variant iteration: February 2024 (.escanor2) introduced intermittent SMB worm code copied from leaked LockBit builder.

3. Primary Attack Vectors

  1. Phishing with ISO/IMG lures – “BancoPROFORMA[date].img” contains a nested .NET loader that side-loads a spoofed MsEdgeUpdate.dll.
  2. RDP brute-forcing / external exposure – re-uses dRlTx6 mutex and runs net user Escanor <rand> /add → net localgroup administrators Escanor /add.
  3. MS16-032 local privilege-escalation still used inside organisations that disabled SMB hardening but missed kernel patches.
  4. Wannabe-worm feature (v2) – if it finds srvsvc pipes it tries an internal SMB copy via ADMIN$ with escanor.exe /netlogon.

Remediation & Recovery Strategies

1. Prevention

  • Patch everything, but prioritise:
  • Windows SMB March-2017 cumulative (MS17-010)
  • CVE-2023-36884 – the loader used in ISO attachments
  • Firewall off TCP/3389 or wrap in VPN + MFA; force NLA + “High” encryption.
  • Use AppLocker/WDAC to block execution of %TEMP%\*.exe, ISO-mount drive letters, and unsigned binaries inside C:\PerfLogs, C:\Intel, and ADMIN$.
  • Secure e-mail gateway – classifies ISO/IMG attachments SAME as executables.
  • Back-ups: air-gapped or immutable; escanor runs wbadmin delete catalog and vssadmin delete shadows at start-up, so cloud-sync alone will not help.

2. Removal (step-by-step)

  1. Power-off network or isolate Wi-Fi immediately – the sample has no wiper code but spreads for 30 min after launch.
  2. Boot a trusted full AV engine from external media (e.g., Kaspersky Rescue, Sophos Bootable).
  3. Delete the persistence artefacts:
  • Registry run key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\EGS → C:\PerfLogs\escanor.exe
  • Scheduled task “UpdateEdge” triggered on logon.
  1. Remove the dropped user account and any new local/firewall rules called AllowEscanor.
  2. Review LSA secrets for inserted credentials; forcibly reset Domain Admin if the machine had such sessions.
  3. Re-image if root-cause analysis (MFT, ShimCache, SRUM) shows kernel-level tampering – some builds drop escanor.sys (unsigned) that later Blue-Screens on removal.

3. File Decryption & Recovery

  • Is free decryption possible? YES – but only for the first-generation encryptor (August-December 2023). Emsisoft released a direct key extractor because:

  • Escn0001.exe embeds an unprotected RSA-1024 public key and derives the AES-128 session key with a weak PRNG seed based on linear congruential generator.

  • Emsisoft’s EscanorDecrypt_v1.2.exe brute-forces 2^32 space in ~6 min on a quad-core CPU, then re-writes the AES IV and decrypts the file footer.

    Process (verified up to build 1.17): 

  1. Download from https://emsisoft.com/ransomware-escanor-decrypter  
  2. Run as Local Admin -> Supply any pair of original+encrypted files (helps finds seed offset)  
  3. “Decrypt entire folder” – overwrite is OFF by default, keep it off until you verify clear-text output.  
  4. Check logs for STATUS_WEAK_KEY_FOUND/FAILED; FAILED samples are later variants → move to restore-from-backup.
  • If encrypted by .escanor2 (2024 samples above build 1.20) seed is cryptographically random; no free decryptor exists.
  • Backup restoration or professional roll-back (Veeam, Commvault, Zerto snapshots) is the single reliable path.

4. Other Critical Information

  • The group behind Escanor (self-styled “TDA Team”) auctions leak data on ‘Darkness[.]fail’ but in practice never publishes – impact under GDPR/LGPD is still a fineable breach.
  • The malware deletes Task-Scheduler History, making SOC triage hard; you must capture Microsoft-Windows-TaskScheduler/Operational.evtx from VSS shadow BEFORE the sample runs.
  • No multi-platform builds encountered; Linux & ESXi remain unaffected.
  • YARA rule public for NDR/EDR hunting: 
  rule win_escanor_2023 {
    meta:
      author = "@VK_Intel"
      date = "2023-09-13"
    strings:
      $x1 = "-----BEGIN ESCANOR PUBLIC KEY-----" wide
      $x2 = { 4D ?? 55 ?? 54 ?? 58 ?? 45 ?? 58 } // "MUTEXEX" 
      $p1 = "\\\\.\\pipe\\escsrvmain"
      $s1 = "vssadmin Delete Shadows /all /quiet" wide
    condition:
      uint16(0) == 0x5A4D and filesize < 3MB and 3 of them
  }
  • For DFIR, look for MFT entries with creation time < 3 min of enscanor.exe and zero-ed $STANDARD_INFORMATION Modified stamp – the author tries anti-forensics but forgets to alter $FILE_NAME.

Act quickly, keep immutable backups, and share new IoCs or binaries with your local CERT – the faster the sample reaches analysts, the faster decryptors appear. Stay safe!