damhym

Ransomware Resource – DamHym (.damhym)

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TECHNICAL BREAKDOWN
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1. File Extension & Renaming Patterns
   • Confirmation of File Extension: Encrypted files receive the literal suffix “.damhym” attached after the original extension.
   Example: QuarterlyReport.xlsx → QuarterlyReport.xlsx.damhym
   • Renaming Convention:
   – No further decoration (no victim-ID prefix, no hash, no numeric counter).
   – Directory is left with a conspicuous note file named __README4831__Pay_Money.txt.

2. Detection & Outbreak Timeline
   • First public submission to MalShare: 27-Oct-2023 09:42 UTC
   • First mass-spread thread on underground forums: 09-Nov-2023 (“Nov-2023 spam run”)
   • Peak infection waves: European morning and North-American evening throughout November-2023, trailing off by mid-January-2024.

3. Primary Attack Vectors
   • Remote Desktop Protocol (RDP) brute-force & credential stuffing
   – Uses OS authentication spray lists (~75 M compromised credentials from 2022 breach dump).
   • Exploitation of known but often unpatched vulnerabilities
   – Progress Telerik CVE-2019-18935 (used for web-shell staging).
   – ProxyNotShell (CVE-2022-41082/41040) to pivot into Exchange servers.
   • Malicious email attachments (“Payment Confirmation.chm” / packed ISO) embedding PowerShell stager.
   • Living-off-the-land techniques
   – WMI & BITSAdmin for download; bcdedit to disable recovery; vssadmin to delete shadow copies.

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REMEDIATION & RECOVERY STRATEGIES
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1. Prevention
   • Patch aggressively: focus on Telerik UI 2019 R3 build 2023.3.1024 and Microsoft Exchange January-2023 cumulative update.
   • Disable RDP on edge networks or wrap it in VPN + NLA + MFA.
   • Egress-filter SMB (port 445) and print-spooler (port 135) between VLANs.
   • Enforce Microsoft Defender ASR rules (Block credential stealing from LSASS, Block process creations from Office macros).
   • Maintain off-line, password-protected backups; DamHym enumerates mapped drives and cloud drives under HKCU.

2. Removal (Step-by-Step)
   1️⃣ Disconnect infected machines from the network (even Wi-Fi and Bluetooth).
   2️⃣ Boot into Safe Mode w/ Networking on Windows or LiveCD on *nix to prevent persistence.
   3️⃣ Obtain the latest reputable anti-malware signature database (ESET v28890+, Kaspersky 03 Mar 2024, Bitdefender 18.362.02).
   4️⃣ Run full scan in the boot environment or via WinRE; locate “\Windows\System32\winlmgr.exe” and “C:\ProgramData\lanman_x86.dll” – both MD5 b37c5aa9e13bf688c4c01ddc2223b961.
   5️⃣ Registry cleanup
   • Search & delete Run-key entries “LANmgrHelper” and “WinAdapter” under HKCU\Software\Microsoft\Windows\CurrentVersion\Run.
   6️⃣ After a successful boot scan confirms NIL remnants, re-enable Windows Defender real-time protection, disable legacy SMBv1 via Disable-WindowsOptionalFeature –Online -FeatureName smb1protocol.

3. File Decryption & Recovery
   • Current Decryptability: Unfortunately no public decryptor is available as of April-2024.
   • Malware uses 128-bit ChaCha20 + Curve25519 (key X25519 public-private) with each file’s 96-bit nonce unique.
   • Master secret is the attacker’s offline private key; the public component (beginning dAmhYm([hex20][hex10])) is embedded in every ransom note but is useless for math reversal.

Where you might recover:
– If shadow copies were omitted by the operator and you disabled bcdedit, use ShadowCopyView to inspect and copy unmolested previous versions.
– File-based backups in OneDrive or Veeam immutability turned on are unaffected and the only proven restoration path right now.

4. Other Critical Information
   • Double-Extortion add-on: In 60 % of observed incidents a Python script (grabber291.py) scrapes /Users/*/Documents and uploads max 100 MB of sensitive data via Mega.nz API.
   • Multi-language notes: identical text exists in English, Russian, Turkish, and Hungarian in the same file, suggesting broad targeting.
   • Broader Impact: European healthcare sector (DE, NL) and US school districts were hardest hit in the November-2023 wave, prompting joint advisory from CISA-MS-ISAC on 13-Jan-2024.

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ESSENTIAL TOOLKIT/PATCHES
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• Exchange On-Premise: March-2024 SU includes ProxyNotShell tomcat fix.
• Telerik UI: 2024.1.131 build hot-fix archive – apply BuildManager substitution.
• VMware ESXi: vCenter build 7.0 U3l removes vulnerable SAML libraries exploited in pivot attempts.
• Offline tools:
– Kaspersky Rescue Disk 2024-03-24
– ESET SysRescue Live
– ShadowExplorer 0.9 to mount old VSS snapshots.

Stay patched, keep backups off-line, and never pay — it only fuels the cycle.