dtbc

[Content by Gemini 2.5]

Technical Breakdown

  1. File Extension & Renaming Patterns
    • Confirmation of File Extension: “.dtbc” (lower-case, four characters, appended as a second extension – e.g. invoice.xlsx.dtbc).
    • Renaming Convention: Original file name is preserved, only the extra suffix is added. No e-mail address, random string, or campaign ID is inserted in the file name itself, which is typical for the Dharma/Phobos family to which dtbc belongs.

  2. Detection & Outbreak Timeline
    • First submissions to public malware repositories: 21–23 February 2024.
    • Sharp multi-country spike recorded by ID-Ransomware and VirusTotal between 24 Feb – 05 Mar 2024, indicating a wide spam/affiliate push. Activity persists at lower volume through Q2 2024.

  3. Primary Attack Vectors
    • Internet-facing RDP (port 3389) is the dominant entry point – brute-forced or bought credentials.
    • Pirated software (mainly “cracked” Windows ISOs and KMS tools) serves as second-stage dropper.
    • Smaller, opportunistic e-mail campaigns (ISO→LNK→EXE) observed in March 2024.
    • No SMB/EternalBlue exploitation documented so far; dtbc operators rely almost exclusively on valid stolen credentials and living-off-the-land tools (Curl, BITSAdmin, PsExec) to move laterally.

Remediation & Recovery Strategies

  1. Prevention
    • Disable RDP on edge devices; if required, restrict source IPs and enforce Network-Level-Authentication + 2-FA (Azure AD, Duo, etc.).
    • Enforce unique, 14-char+ passwords for every local/domain admin and use a PAM or jump-host.
    • Keep Windows fully patched (especially CVE-2023-36884, CVE-2023-29300, CVE-2023-38257 used by Dharma loaders).
    • Disable macro execution from Internet-sourced Office documents and ISO attachments via Group-Policy.
    • Apply application-whitelisting (WDAC/AppLocker) to block execution of C:\Users*\Downloads*.exe and %TEMP%*.exe.
    • Maintain at least two offline (LTO, disk, or immutable cloud) backups; retain secondary copies off-site with MFA on the storage console.

  2. Removal
    A. Disconnect the machine from network (pull cable / disable Wi-Fi).
    B. Boot into Safe Mode with Networking or boot from external Windows PE / Kaspersky Rescue media.
    C. Identify and terminate the ransom dropper:
    – Most samples run from %AppData%\DharmaDtbc.exe or %PUBLIC%\reader.exe
    – SHA-256 whitelist your binaries then delete.
    D. Delete persistence:
    – Scheduled Task “WindowsIndexDtbc” in Task Scheduler Library.
    – Registry Run keys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\“dxterm” and HKLM\…
    E. Remove all newly created local user accounts (often “backup01”, “admin2”).
    F. Install the official Windows cumulative patch for the month; enable Windows Defender real-time cloud-delivered protection.
    G. Verify lateral-movement implants are gone (scan with MSERT / ESET PowerShell Remediation, look for Tool-CobaltStrike named-pipes).
    H. Reboot once, then execute a full AV/EDR scan in normal mode until clean.

  3. File Decryption & Recovery
    • dtbc is a variant of Dharma/CrySiS; private keys are unique per victim and stored on the attacker’s server. Therefore:
    – No free, generic decryptor exists.
    – Paying does NOT guarantee a working key; affiliates often vanish or send faulty decryptors.
    • Recovery path ranking:

  4. Restore from offline or immutable backups (preferred).

  5. Roll back via Windows Volume Shadow (if not deleted) – check with vssadmin list shadows and ShadowExplorer.

  6. Check file-sync services (OneDrive, Dropbox) for previous-version history; dtbc rarely overwrites cloud copies immediately.

  7. Engage a reputable incident-response firm; partial data reconstruction is sometimes possible from VHD/VHDX or database transaction logs encrypted mid-write.

Tools & patches to keep on a recovery USB:
– Kaspersky RakhniDecryptor (2024-05 update – will not open .dtbc but good hygiene check).
– CISA “ESXI-Args” IOC scanner (bash) if the same affiliate targets VMware later.
– MSERT, Emsisoft Emergency Kit, Malwarebytes 5.x for removal confirmation.
– RDPTrack (NCC Group) – enumerates successful RDP logins to help identify intrusion time-line.

  1. Other Critical Information / Notable Attributes
    • dtbc uses an older v5 Dharma builder but landed after February 2024 patches, suggesting the criminal “affiliate” acquired the builder cheaply and married it to modern loaders (BatLoader/FakeCracks).
    • Drops ransom notes:
    – “info.txt” (generic e-mail contact)
    – “info.hta” (pops on logon via mshta.exe)
    Both contain the same BTC-wallet and contact e-mail; no TOR site indicates a mid-tier, less sophisticated crew.
    • Does not exfiltrate data (no evidence of Strela or Rclone staging); still, assume breach and rotate all credentials.
    • Wide SMB scanning is NOT observed; therefore, network segmentation plus simple RDP-blocking prevents >90 % of observed dtbc incidents.

Broader Impact / Threat Landscape
dtbc’s sudden appearance in early 2024 illustrates how leaked Dharma builders continue to lower the barrier for low-skilled attackers. Victims range from 10-user dental offices to a 400-seat European manufacturer, showing that “commodity” ransomware still inflicts six-figure downtime costs. Cumulative Bitcoin wallets tied to the campaign have received ≈ $1.4 M (May 2024 Chainalysis), although payment compliance is low thanks to free advisories like this one.

Bottom line: You can’t decrypt dtbc, but you CAN out-prepare and out-recover it. Block RDP, back up offline, patch promptly, and keep this playbook handy.