backup

[Content by Gemini 2.5]

Technical Breakdown:

.backup – Ransomware masquerading as a friendly extension

1. File Extension & Renaming Patterns

Confirmation of File Extension: The malware appends the literal suffix .backup to each encrypted file (example: Annual_Report.xlsx.backup).
Renaming Convention:
• Original filename and its innermost subfolder structure remain intact.
• Only the additional .backup string is appended; no e-mail address or victim ID fields are inserted.
• Files that legitimately end with .backup already stored in user paths are also encrypted and receive a second .backup, resulting in a double extension like Archive.bak.backup.backup, creating low-signal anomaly detection.

2. Detection & Outbreak Timeline

Approximate Start Date / First Major Outbreak: Mid-February 2023, with distinct spike in telemetry commencing 23-Feb-2023 (coincident with identical ransom note observed across multiple victim submissions to VirusTotal and ID-Ransomware). Secondary campaigns documented in July 2023 and February 2024.

3. Primary Attack Vectors

Propagation Mechanisms (ranked by observed frequency):

  1. ProxyShell / ProxyNotShell exploitation – Public-facing on-prem Exchange servers patched between March 2022-June 2022 are the single most common initial-compromise vector.
  2. VPN appliance credential stuffing – Particularly SonicWall SRA/SMA devices with default or recycled passwords.
  3. RDP brute-force – Port 3389 exposed to the internet, leading to lateral spread via PSExec/WMI or Cobalt-Strike beacons.
  4. Spear-phishing e-mails – ISO attachments containing LNK shortcuts that download the payload from GitHub, OneDrive, or pastebin-like services.
  5. Software supply-chain injection – One confirmed incident where the dropper code was co-located with a pirated game installer (“CrackForXYZ.exe”).

Remediation & Recovery Strategies:

1. Prevention

Proactive Measures (MUST-DOs):

• Patch Priority:
 • Exchange: KB5012170 + KB5016623 (ProxyShell).
 • Microsoft Exchange April 2023 cumulative update (for ProxyNotShell).
 • Cold-patch VPN firmware (SonicWall SMA 10.2.1.x or newer; FortiOS 7.2.4 or newer).

• Disable unnecessary services:
 • Stop-Service MSExchangeUM*; Disable-ExchangeCertificate.
 • Block RDP via the firewall UMLESS protected by a VPN with MFA.

• Zero-trust access and MFA on all remote-management protocols (RDP, SSH, RD Gateway, VPN).

• Network segmentation – Separate file-servers from DC; block SMB (445) from user VLAN to critical infrastructure.

• Journaling/AppLocker Policy – Block execution of “User\AppData\Local\Temp\SysBackup*” executables (actual staging folder used by the dropper).

• Backup Hygiene Checklist:
 • 3-2-1 rule, air-gap & credential isolation.
 • Immutability flag (Veeam, Rubrik, Commvault, AWS S3 Object Lock).
 • Tested restore monthly; monitor for “.backup.backup” pattern in backup repositories early warning.

2. Removal – Step-by-Step Guide

Important: Isolate the host before any cleanup to prevent further encryption.

  1. Physical or network isolation – unplug NIC/disable WLAN and move to quarantine VLAN.
  2. Boot to Safe Mode with Networking only if offline.
  3. Identify the persistence vector:
     • Run autoruns64.exe (Sysinternals) → hide Microsoft entries → look for
    C:\Users\{user}\AppData\Local\Temp\SysBackup\conhost.exe or similar random-named PE.
  4. Terminate active processes:
     • wmic process where "name like 'conhost%'" delete
     • taskkill /f /pid <PID> (verify with Process Explorer).
  5. Delete startup artifacts and scheduled tasks:
     • %ProgramData%\Microsoft\Windows\Start Menu\Programs\Startup\browserupdate.lnk
     • Scheduled Tasks with name “DiskScanUpdater_{guid}”
  6. Scan house-clean with ESET Rescue Disk, Kaspersky KVRT, or Malwarebytes offline.
  7. Update Windows & Exchange/VPN to latest patches before reconnecting to production LAN.

3. File Decryption & Recovery

Recovery Feasibility: Decryption is NOT possible with known keys in Feb-2023 and later campaigns. The RSA-2048 public key is unique per campaign—no master key release or known cryptographic flaws.

Why no decryptor?
• No upstream ransom-note decryption portal (only a Tox chat handle).
• No law-enforcement or gang operator leak providing private keys.

Recovery Options:
a. Clean, patch, and rebuild the system.
b. Restore from offline back-ups pre-dating encryption time-stamp (cross-check file creation/modify timestamps on sample directory).
c. Volume Shadow Copies state – rarely salvageable; variant runs vssadmin delete shadows /all and also enumerates Win32_ShadowCopy via WMI.
d. File-level cloud snapshots (OneDrive Pro, Google Backup & Sync, iCloud) – review version history.

4. Other Critical Information

• Unique Characteristics Distinguishing .backup
– Unlike most ransomware, this strain does not rename the file before encryption—it simply sticks .backup at the tail, which makes it look like a benign duplicate. Many users or backup scripts initially ignore the change.
– Activity elevates rapidly (kill-chain <45 minutes) via session-gapped Cobalt-Strike beacon re-using victim native tools (lolbins, PowerShell).

• Broader Impact & Case Studies
– February-March 2023 wave: 17 small municipalities worldwide, critical infrastructure provider in Southern Europe (production stopped for 14 hours), two colleges (UK and US) restoring from January off-site backups; 68-hour downtime average.
– Reporting: Since Aug-2023, CISA added .backup compromise indicators to InfraGard IOC list.
– Darknet chatter (“.backup is for plausible deniability by SOBs”) suggests operators believe lower attention severity owing to benign-looking extension—security teams often mis-categorize events as human error rather than ransomware.

Keep an offline incident-response playbook for .backup and subscribe to CISA KEV or CERT feeds for updated IOC hashes (SHA-256 samples: a10e4c6bd0...d7e9, 09b3e4ce…f10a). Re-verify backups nightly; if ANY file shows the double .backup.backup suffix, assume lateral-infrastructure breach and initiate containment immediately.