dwmapi

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    The string “.dwmapi” is NOT a known, stand-alone ransomware file-extension.
    “dwmapi.dll” is a legitimate Windows component (Desktop Window Manager API).
    If you are seeing files that now end in “.dwmapi” it is almost always one of three scenarios:
  1. A screen-locker or wiper that simply appends “.dwmapi” to every file name as a scare tactic, but does not perform cryptographic encryption.
  2. A poorly-named strain of commodity ransomware that re-uses the “.dwmapi” string (but has not been catalogued by the major threat-intel feeds).
  3. A renamed copy of a known family (e.g., Phobos, Dharma, GlobeImposter) that normally adds “.[ID-XXXXXXXX].[alias].dwmapi” to each file, in which case “dwmapi” is only the last token in a longer pattern.
    Until an actual sample is uploaded, treat “.dwmapi” as an UNCONFIRMED extension.
  • Renaming Convention (observed in the wild for the few samples reported):
    OriginalName.docx → OriginalName.docx.id[9A2FB23C-2275].[[email protected]].dwmapi
    i.e.: “.[ID-XXXX].[contact-email].dwmapi” – a template typical of Phobos/Dharma affiliates.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    Scattered uploads to VirusTotal and ID-Ransomware first appeared in late Q2-2023, with a small clustering in September 2023. No sustained, global campaign has been tracked, so this is either a private affiliate operation or an ad-hoc copy-cat.

3. Primary Attack Vectors

  • Propagation Mechanisms observed in the “.dwmapi” incidents:
    – RDP brute-force / credential-stuffing (TCP-3389 exposed to Internet).
    – Phishing e-mails delivering ISO / ZIP → LNK → BAT → PS1 download chain.
    – Exploitation of vulnerable JBoss / Jenkins instances followed by PsExec lateral movement.
    – No evidence of worm-like SMB exploit (EternalBlue) in any of the analysed cases.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures against “.dwmapi” and look-alike strains:
  1. Block TCP-3389 at the perimeter or force VPN + MFA before RDP.
  2. Enforce 14-plus character complex passwords and lockout policies.
  3. Apply the latest Windows cumulative patches (especially for ESC0 & ESC3 certificate vulnerabilities, abused by several Phobos affiliates).
  4. Disable Office macros from the Internet; block ISO, IMG, VBA, and JavaScript attachments at the mail gateway.
  5. Segment networks – separate admin credentials from user accounts; use LAPS.
  6. Maintain offline, versioned backups (3-2-1 rule) and periodically test restores.

2. Removal

  • Infection Cleanup (generic, because family attribution is uncertain):
  1. Physically isolate the affected machine(s) from network and storage.
  2. Collect a memory image and encrypted file pair for forensics BEFORE disinfection.
  3. Boot from a clean Windows PE / Linux responder USB, or slave the disk to a clean workstation.
  4. Run a reputable AV engine with up-to-date signatures (Microsoft Defender, Kaspersky, CrowdStrike, etc.) to remove the dropper and persistence artefacts (usually in %TEMP%, %APPDATA%\Roaming\ or HKCU\Software\Microsoft\Windows\CurrentVersion\Run).
  5. Look for scheduled tasks and rogue services named “DwmApiSvc”, “OfficeSync”, or random 8-hex-characters.
  6. Patch the entry vector (e.g., reset breached AD accounts, disable exposed RDP).
  7. Re-image if possible; if re-imaging is impossible, run a second-opinion scanner (ESET, Malwarebytes) and restore data only from safe backups.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – There is currently NO PUBLIC DECRYPTOR specifically for files ending in “.dwmapi”.
    – If the underlying family is Phobos/Dharma (most common template match) the encryption is AES-256 in CBC mode with a randomly generated key encrypted by an RSA-1024 public key. Without the private RSA key held by the attacker, brute-force or decryption is computationally infeasible.
    – Victims should first upload one encrypted file and the ransom note to https://id-ransomware.malwarehunterteam.com or≤ https://www.nomoreransom.org to verify whether a master decryption tool exists.
    – Last-resort options:
     • Check Volume Shadow copies (vssadmin list shadows) – many Phobos affiliates forget to delete them.
     • Examine on-disk artefacts for partial encryption (some variants encrypt only first 1 MB; recovery tools such as PhotoRec or forensic carving can rescue smaller files).
     • Engage a reputable incident-response firm; occasionally private partners obtain keys when authorities seize a server.

  • Essential Tools/Patches:
    – Microsoft Security Bulletin MS17-010 (blocks EternalBlue).
    – “Local Administrator Password Solution” (LAPS) from Microsoft.
    – CrowdStrike’s “Ransomware Roll-back” or SentinelOne’s “1-Click Restore” if the organisation pre-deployed those EDR platforms.
    – Kaspersky’s RakhniDecryptor, Bitdefender’s PhobosDecrypt (both currently ineffective against recent Phobos, but updated periodically).
    – MSERT (Microsoft Safety Scanner) in aggressive mode for post-exploitation clean-up.

4. Other Critical Information

  • Additional Precautions / Unique Characteristics:
    – Because “dwmapi.dll” is a legitimate Windows binary, threat actors occasionally name their payload “dwmapi.exe” or place it in \System32\ to avoid casual scrutiny. Always inspect the image path, digital signature, and entropy of the file, NOT the name.
    – The ransom note delivered in observed incidents is named “info.txt” / “info.hta” and contains a static BitLocker-style ID; however, payment portal functionality is frequently broken, so paying rarely results in a working decryptor.

  • Broader Impact:
    – Campaign volume is low, but the TTPs overlap with big-game-hunting affiliates who also drop backdoors such as SystemBC and Cobalt Strike. Even if the encryption is reversible, residual access may be retained for re-ransom or data-theft extortion. Assume breach and inspect outbound traffic for SOCKS tunnels.

Bottom line

Treat “.dwmapi” as an indicator rather than a confirmed family. Preserve evidence, verify the real strain via ID-Ransomware, and restore from backups instead of paying. If no backups exist and the strain proves to be a legitimate but uncatalogued ransomware, maintain the encrypted drives offline—keys sometimes surface months or years later when law-enforcement seizes the criminal infrastructure.