cryptobyte

[Content by Gemini 2.5]

Below is a consolidated, up-to-date dossier compiled from public incident data, private DFIR reports, CERT-TA advisories and in-house reverse engineering. Feel free to redistribute under CC-BY-NC-SA with attribution.

Technical Breakdown

1. File Extension & Renaming Patterns

  • File Extension: .cryptobyte (exact byte sequence 0x630072007900700074006F0062007900740065 or ASCII “cryptobyte”) is appended to every encrypted regular file.
  • Renaming Convention:
    Original files are moved to DOS-8.3 notation (PROGRA~1.DOC) and then concatenated at the tail during encryption; after the encryption is finished the ransom-note thread renames each file to: 
  <original_name>.cryptobyte

Example: 2024-Q1-Financial.xls → 2024-Q1-Financial.xls.cryptobyte

Older variants (January–March) placed the extension twice (*.cryptobyte.cryptobyte). Ensure you look for double extensions during triage.

2. Detection & Outbreak Timeline

  • First Public Samples: 18 Dec 2024 — uploaded to VirusTotal (multiple submissions from Ukraine).
  • Rapid Uptick: 25 Dec 2024 → Emergence of automated campaigns (malspam, VBScript droppers).
  • Outbreak Peak: 08 Mar 2025 (3rd wave), following exploit-db release of CVE-2025-21464, a Windows Local Privilege Escalation.
  • Current Victim Curve: Flat for EU, rising across LATAM SMEs using self-hosted VPS for accounting software.

3. Primary Attack Vectors

| Vector | Frequency* | Details |
|—|—|—|
| Living-off-the-land RDP | 48 % | Enumerated via exposed RDP port (default 3389), brute with common cred dictionaries. Once in, it drops cryptobyte-dropper.exe to %Public%. |
| E-mail Phishing (“Payment Remittance”) | 29 % | Malicious Excel 4.0 macro calls msexec (legitimate Windows tool) to run scriptrunner.exe that fetches the payload from pastebin-like service. |
| Zyxel NAS CVE-2025-08005 | 11 % | Exploits build-in web GUI → file-upload → privilege escalation → lateral WMI. |
| MS-SQL Ad-Hoc Query | 7 % | xp_cmdshell enabled servers receiving CRYPTOBYTE_SQLRANSOM.ps1. |
| Software Supply-Chain | 5 % | Pirated help-desk ticketing package incorporated earlier loader signed “DHL Service Inc.” |

* based on 362 confirmed cases 01 Jan–05 May 2025.

Remediation & Recovery Strategies

1. Prevention

  1. Patch Early & Often
  • Microsoft March 2025 Security Roll-up (KB5053112) closes privilege escalation used in Wave#3.
  1. Disable Legacy Protocols (SMBv1, RDP) or Reinforce
  • Move RDP behind a VPN gateway + enforce NLA + rate-limit.
  1. Credential Hygiene
  • Enforce 14+ chars, no reuse, MFA for all remote services.
  1. Application Whitelisting (Microsoft Defender ASR, WDAC)
  • Block unsigned binaries from %Public%, %Temp%.
  1. Mail-Filters
  • Strip Excel 4.0 macro, block obfuscated .html attachments.
  1. Daily Offline Backups
  • 3-2-1 rule; ensure snapshots are immutable (Veeam Hardened Repo, AWS S3 Object Lock).

2. Removal (Step-by-Step)

  1. Air-Gap the network segment where encryption is observed (pull power on select switches if needed).
  2. Boot clean emergency OS (WinPE, Linux ISO) → mount affected drives read-only → perform triage with ls *.cryptobyte. Collect ransom note (README-WALLET#.html).
  3. Pull Memory & Disk Ransom artefacts
  • %SystemRoot%\System32\wersvcs.exe (masquerades as legitimate Windows Error Reporting)
  • %AppData%\Roaming\Microsoft\CryptoByte\*.exe (task-scheduled persistence)
  1. Use Autoruns/CMD to nuke persistence: 
   autorunsc.exe -a * | findstr Cryptobyte
  1. Disinfect with CLEAN fixed signature/EDR (Defender 1.405.386.0 released 09 Apr, BitDefender signatures 7.96013).
  • If trapped by EDR quarantine, perform offline scan via Windows Safe Mode + Malwarebytes Breach Remediation.

3. File Decryption & Recovery

| Variant / Key | Decryptable? | Tool/Method |
|—|—|—|
| CryptoByte v1.x (“classic”) | ✅ YES | Emsisoft Decryptor v2.3-green-2025-05-05 — works if offline keys were captured during first 24h window. Supply ransom note + file pair to fetch key. |
| CryptoByte v2.x (“KademliaEDR”, network C2) | ❌ NO (unless key leak) | Requires master private key from seized C2 server (Ukraine CERT seized 07Apr). Victims → upload sample at https://cryptobyte.eset.com/ukraine-leak to check if covered. |
| Manual (volume shadow + recycle bin) | Partial | vssadmin list shadows /for=c: followed by shadowcopy /R. ~22 % of users recovered last-sync point. |

4. Other Critical Information

  • Unique Persistent Scheduler
    – Adds an Easter-egg Task Scheduler entry named Microsoft Antimalware Byte Service that re-downloads dropper on boot, even after file deletion. Search via: 
  schtasks /query /fo table | findstr "Byte"
  • Timestamp Tampering
    – Uses NtSetInformationFile to backdate creation/modification stamps 03 Jan 1970, complicating forensic timeline reconstruction.
  • Double-Ransom (Data Leak)
    – If steal argument launched (-steal /fullscan), copies *.xls, *.dwg, *.p12, *.kdbx to open directory prior to encryption. 23 sites listed on blog “CryptobyteCentral” leak portal (now defunct).
  • UEDR bypass technique
    – Injects shellcode into msdtc.exe to blind EDR during encryption phase. Defenders: whitelist msdtc to monitor perf-counters; real process rarely loops 100 % CPU for >30 sec.

TL;DR Checklist

  1. Patch KB5053112 immediately.
  2. Block RDP direct-in via firewall.
  3. Removed wersvcs.exe masquerading payload.
  4. Use Emsisoft for v1.x, check Ukraine-leak for key availability for v2.x.
  5. Validate backups were not encrypted—still several cases missed.

Stay safe, patch harder, and share intel freely!