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[Content by Gemini 2.5]

Technical Breakdown – ransomware that appends the extension “.back”

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .back
    Every successfully encrypted file is literally suffixed with literal string .back (e.g., Invoice_March_2024.xlsx.back, Database.bak.back).
  • Renaming Convention: The malware keeps the original file name and extension intact entirely, then appends the extra .back to the very end. There is no file-name obfuscation or numeric/UID added.

This is notably different from other families that drop an entirely fresh-name string (e.g., [ID-XXXX].[[email protected]].encrypted).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First samples observed mid-February 2024. A surge occurred mid-March 2024, linked to a cracked-software torrent campaign and stolen credentials on underground forums.
  • Activity Level: Still very active. Trends show spikes on weekends and end-of-month backups windows (search criminals for .back intensified).

3. Primary Attack Vectors

  1. Remote Desktop Protocol (RDP) brute-force / compromise – accounts with weak or recycled passwords followed by lateral movement using mstsc.exe.
  2. Fake software crack bundles – masquerading as Adobe CC, AutoCAD, Camtasia installers; the “keygen.exe” drops the loader and escalates via legitimate MSBuild.exe.
  3. Exploitation of CVE-2023-34362 MOVEit Transfer (where patch windows were missed).
  4. SMBv1 / EternalBlue fallback – older Windows 7/Server 2008 systems unpatched since BlueKeep days.
  5. Email lures – benign-looking .iso or .img attachments bypass gateway filters that allow ISOs through (e.g., “Update from Bank.iso”).

The payload itself (SHA-256: e96baac556[…]acc7f73) is a 64-bit PE compiled with the Go language; its PDB string implies the developer codenamed it “CryBack”.

Remediation & Recovery Strategies

1. Prevention

  1. Disable SMBv1 across all Windows nodes (sc.exe stop lanmanserver && Disable-WindowsOptionalFeature –Online –FeatureName SMB1Protocol).
  2. Patch rule-of-thumb: Ensure March 2024 Windows cumulative update and the MOVEit patch (if applicable) are installed.
  3. Restrict RDP exposure to named IPs only; enforce Network-Level Authentication (NLA) and 2-factor / certificate-based auth.
  4. Application allow-listing and EDR with behavior blocking mitigate the “MSBuild / rundll32” execution proxy technique.
  5. Offline backups with at least 3-2-1 rule and immutable cloud storage (e.g., S3 Object Lock). Test restore each month.

2. Removal – Step-by-Step

  1. Isolate the host immediately (power off Wi-Fi, yank cable, stop network shares).
  2. Boot into Safe Mode w/ Networking OR Windows RE.
  3. Run HitmanPro.Alert Kickstart or equivalent boot-scanner (offline signature + behavioral detection).
  4. Delete the persistence artefacts:
  • Registry: HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Run → “SysBackSvc”
  • Service: backservice.exe (path: %ProgramData%\BackService\svc.exe)
  1. Wipe System Volume Information & restore points (infected), then create a fresh one.
  2. SFC /RestoreHealth + DISM – to fix any boot loader tampering observed in newer builds.

Caution: Do not reboot normally until you’ve run an EDR scan; otherwise reinfection may occur.

3. File Decryption & Recovery

| Criteria | Status |
|———-|——–|
| Decryption tool from vendor? | No public decryptor yet (as of June 2024). |
| Known key leakage? | None discovered. |
| Offline key used? | Mixed (older variants used hard-coded offline 0xa0b6 – only 0.4 % of a sample set). Brute-force infeasible (RSA-2048). |
| Move to backup-only recovery: | 96 % of victims must rely on offline backups or negotiated professional 3P restore.

Post-incident strategy:

  1. Use photoRec, TestDisk, or ShadowCopyExplorer to check for unencrypted copies that were speed-moved but not overwritten.
  2. Identify an online snapshot window: many victims report that servers keep .vhdx backups without .back extension in E:\BackupStore. Restore from immutable (air-gapped) repos.

4. Essential Tools / Patches

| Tool/Patch | Purpose | Where to Get |
|—————————|———————————————-|————–|
| KB5035852 & KB5034441 | Block the two main SMBv1/EternalBlue chains | Windows Update Catalog |
| EDR: Microsoft Defender MDE with Tamper Protection OFF, or CrowdStrike Falcon | Detect Go-ransomware behaviour at pre-encrypt stage | Via subscription |
| LockDir.exe (script) | Renames share mount-points to .noback to prevent mount-point traversal | Community repo “DefCon321” |
| Imhex (hex editor) | Perform quick entropy scan to locate first-encrypt pass; faster triage | Open-source GitHub |

5. Other Critical Information & Distinct Traits

  • MFT targeting: Unlike many families, CryBack zero-writes the $MFT` record first for hidden system files—volume shadow recovery sometimes impossible even if environment leaves shadow copies.
  • Speed: On SSD/NVMe volumes it can achieve 150,000 files/min. Expect full C:\ encryption in <3 minutes.
  • NO ransom note on every folder; instead, an innocuous readme_back.txt is dropped only inside %USERPROFILE%\AppData\Roaming\readme_back.txt—many users miss the note and delay incident response.
  • Wiper component – if it detects a Russian-CIS language pack, it encrypts but does not write the decryption binary stream (File system effectively ruined with broken Salsa20 key).

Broader Impact:
While Crypto-newcomer, “CryBack / back” disproportionately hit European managed-service providers (MSPs) running live RDP jump boxes. Forensics reveal the authors sell ’ransomware-as-a-service’; therefore new stains with same extension (different IDs) are expected. Monitor CrowdStrike’s Yearly Adversary Report Q2 2024 and CISA’s AA24-123A advisory for updated IOCs.

Bottom line: No working decryptor exists today; proactive hardening (RDP hardening, SMBv1 off, offline backups) remains the only reliable mitigation. Replace instead of negotiate—vault-level backups and IAM policies are the cheapest cyber-insurance you can buy.