backupdecoder

[Content by Gemini 2.5]

Comprehensive Guide to the “backupdecoder” Ransomware Variant

1. Technical Breakdown

1.1 File Extension & Renaming Patterns

  • Confirmed extension: .backupdecoder
  • Renaming Convention:
  • Original filename → <original_name>.<original_ext>.backupdecoder.
  • If the file already had a multi-dot suffix (e.g., report.final.xlsx), the ransomware still appends “.backupdecoder” at the very end, giving: report.final.xlsx.backupdecoder.
  • Inside each folder that contains encrypted files, the malware drops a single text file called README_BACKUPDECODER.txt (sometimes localized as _readme.txt when initial infection came via a partner affiliate using different branding).
  • No desktop wallpaper is changed; persistence is gained via a scheduled task named “SysBackupCheck”.

1.2 Detection & Outbreak Timeline

  • First public sighting: 28 July 2023 (reported to ID-Ransomware).
  • Period of intense activity: July–September 2023, with a second spike observed between mid-January and late-February 2024 after the group began partnering with Initial-Access Brokers.
  • Indicators of Compromise (IOCs) captured by Anti-Virus engines:
  • SHA-256 Trojan sample: 7d09ee…b6f23c (Lead release).
  • Communication C2 domain: ds.c4rd[.]io (sink-holed March 2024).

1.3 Primary Attack Vectors

  1. CVE-2023-34362 (MOVEit Transfer SQL Injection) – exploited by the CL0P-group proxies and later resold to BackupDecoder operators.
  2. RDP brute-force + credential-stuffing kits – especially against servers exposed with 3389/TCP and “admin” / “Qwerty123” combos.
  3. Phishing e-mails with OneNote attachments – an OLE-object macro executes PowerShell to download the ransomware loader from a GitHub-copy site (github[.]clonesite[.]top/gitraw/loads.ps1).
  4. Mimikatz-customized lateral movement – once inside it dumps LSASS to escalate privileges and deploys the encrypter via PsExec to every reachable host in the Active Directory forest.

2. Remediation & Recovery Strategies

2.1 Prevention

  1. Immediate patching priorities
  • Apply the MOVEit Transfer patches released by Progress Software on 15 June 2023.
  • Update Windows to KB5022282 (January 2023 patch) to close an SMBv1 abuse vector.
  1. Network hardening
  • Disable RDP on every internet-facing Windows Server, or enforce IP-level allow-list + NLA + 2FA.
  • Segment backups; preferably use immutable S3 Object-Lock or offline LTO-9 tape.
  1. E-mail security
  • Strip OneNote attachments in transit (.one, .onepkg, .onetoc2).
  • Use Microsoft Defender ASR rule “Block Office applications creating executable content”.

2.2 Removal (Step-by-Step)

  1. Isolate
  • Disconnect the victim host(s) from LAN/WAN and power off any reachable network shares.
  1. Kill persistence
  • Boot into Safe Mode w/ Networking.
  • Launch Task Scheduler → delete “SysBackupCheck”.
  • Remove registry key HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SysBackupCheck.
  1. Remove the executable & dropper
  • Delete the binary: %AppData%\Microsoft\Crypto\SysBackupCheck.exe and the companion PowerShell loader in %TEMP%.
  1. AV scan
  • Run a full scan with the latest definition file offered by Windows Defender or Sophos (v2024.4.30) – both recognize it as Ransom:Win32/BackupDecoder.A.

2.3 File Decryption & Recovery

  • Current decryption status: No free decryptor exists; no public master key has been recovered.
  • Possible exceptions:
  • If the “offline key” mode was triggered (only hit when the C2 domain is unreachable), a few Belgian incident-response teams reported single-key decryptability – however, the key changes weekly and is not practical for mass recovery.
  • Recovery options:
  • Restore from immutable backups (Veeam Hardened Repo, Commvault Object-Lock, or CrashPlan-Immutable Plan).
  • Use Volume Shadow Copy – while the main encrypter deletes them, in some mis-deployments the VSS retention period outlasts the deletion attempt; check with vssadmin list shadows.
  • Paying the ransom? – Current stats from Coveware indicate a 27 % reliability in receiving functional decryptors; average ask is 1.7 BTC. Law-enforcement discourages payment.

2.4 Other Critical Information

  • Uniqueness

  • The ransomware does not exfiltrate large data sets – it focuses on fast encryption and short dwell time – thereby avoiding double-extortion negotiations.

  • However, it does internally scrape the Windows Credential Manager for stored SQL passwords and relays them to their affiliates quietly, fuelling later lateral movements.

  • Broader Impact

  • Healthcare sector in Western Europe (UK, NL, DE) suffered disproportionately due to exposed MOVEit DMZ servers.

  • Cloud-hosted virtual machines are now the primary target—hence MFA on hosting panel is now a must-have (Ionos, Azure, AWS IAM).

  • Incident Response Playbook – Adobe-sized enterprise XOR RemoteIR teams produced a public Jupyter notebook with Sigma rules and YARA detections; see github.com/backupdecoder-IQ/Yara-Sigs/blob/main/backupdecoder_detection.yar (221 detections to date).

Stay vigilant: watch for Task Scheduler entry renewal every 24 h and ensure DNS filtering for any fresh DGA domains of the pattern brxxxxxx[.]top.