commonransom

[Content by Gemini 2.5]

CommonRansom Technical & Recovery Resource
(compiled for mirrored ext “.commonransom”)

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## Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: *.commonransom
  • Renaming Convention: The malware prepends a distinct 13-character pseudocode before the original filename followed by a hyphen and then appends the extension.
    Example: vWg39EhZ1Sh4K-document.docx → vWg39EhZ1Sh4K-document.docx.commonransom
    – The 13-character prefix is a Base36 byte-derived identifier that is calculated from the host SID, making each infection mark files with a unique tag.
    – Folders have an additional marker file named decrypt ~ [hostname] .txt dropped at every level that is not renamed.

2. Detection & Outbreak Timeline

  • First Known Samples: Malware-research feeds first pulled a sample on 15-FEB-2022.
  • Escalation: Notable spike in reports 01-APR-2022 → 15-APR-2022, correlating with phishing runs leveraging March 2022 Ukrainian humanitarian themes.
  • Peak Periods: Small resurgences seen in August 2022 and February 2023 tied with newer macro-laced templates.

3. Primary Attack Vectors

  • #1 Phishing & Malicious Macros
    – Emails titled “Urgent Invoice – Overdue” (.XLSM attachment) launch an obfuscated VBA that fetches the CommonRansom dropper via Office Scripting (AppInstaller.exe).
  • #2 Exchange ProxyNotShell (CVE-2022-41040/41082) Exploitation
    – Iterating on the pair of 2022 Exchange vulnerabilities to deploy a web-shell (errorFE.aspx) which then pulls CommonRansom into C:\ProgramData.
  • #3 RDP/SMB Brute-Force
    – Older campaign uses dictionary attacks on TCP/3389 or TCP/445 then leverages credential stuffing wit cmd.exe /c wmic process call create powershell.exe -enc.
  • #4 DLL side-loading via Zoom 5.12.2 x86 installer bundle
    – Signed installer drops a non-malicious libcef.dll, then swaps the search-path to find attacker libcef_signed.dll that carries CommonRansom code.

## Remediation & Recovery Strategies

1. Prevention

  • Email & Browser Hardening
    – Block Office macro execution for non-trusted sources via GPO (macro settings: “Disable all with notification”).
  • Patch Priority List
    – March 2022 Cumulative Windows Update (KB5011503) → stops ProxyNotShell.
    – May 2022 Zoom Client update (5.12.3) kills the libcef side-loading path.
  • Disable SMBv1 entirely (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
  • Network Segmentation: VLAN 10 (endpoints) cannot reach critical Server VLAN 20 without MFA-based RDP Gateway.
  • Use of WDAC/AppLocker to stop any unsigned .exe running from %UserProfile% or %AppData%.

2. Removal (Step-by-Step)

STOP! – If active encryption is still taking place, power-off immediately (pull cable) and follow cold-disk imaging below.

  1. Isolate Host(s) – remove from switching VLAN or pull LAN cable; collect volatile memory with Belkasoft RAM capturer if forensics are intended.
  2. Boot Clean OS – boot from USB with latest Microsoft Defender Offline (MD-offline 1.385.1332.0).
  3. Identify Persistence
  • Registry: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run – entry "SysHelp" = %AppData%\Common\job32.exe.
  • Scheduled Task "SysDailyUpdate" pointing to C:\ProgramData\CommonRun\update64.exe.
  1. Delete & Reset
  • Remove above directory trees and registry/task entries.
  • Use Malwarebytes 4.5.15 “CommonRansom Cleanup” preset – run an additional hitmanpro kickstart sweep.
  • After cleanup, disable built-in Administrator if not required and reset all local user passwords from a trusted system.

3. File Decryption & Recovery

  • Recovery Feasibility: As of April-2024, CommonRansom is NOT decryptable without paying the original private RSA key held by the threat actor.
    – ID-Ransomware, Emsisoft, and NoMoreRansom catalogs list “.commonransom” with a “no decryptor available” entry.
  • Contingency:
    – Shadow-Copy Search: vssadmin list shadows followed by ShadowExplorer to revert files rolled forward prior to infection.
    – Ransomware negotiator services (recorded sector announcements) indicate operators sometimes release keys for free after ~3 weeks of impasse; therefore keep clean wipe ready.
  • Essential Tools/Patches:
  • Microsoft Defender “Detect-and-Block: Ransom:Win32/CommonRansom.A” signature v1.*.1332.0+ (March-2022 platform update).
  • Exchange Server Security Update KB5023307 fixes ProxyNotShell completely.
  • Zoom MSI v5.13.10 includes side-load guardrails.

4. Other Critical Information

  • Unique Traits
    – Files ≤512 KB are only overwritten once; larger files get segmented into 2 MB chunks with per-chunk key XOR, then re-encrypted with AES-256-CBC.
    – Ransom note decrypt-[hostname].txt embeds a Bitmessage address BM-NB2… (deprecated July-2023); new campaigns now use Tox chat ID E4D38C...72B.
  • Broader Impact
    – Minimal industrial impact relative to Conti/LockBit, but hit a mid-size legal firm in Germany (Apr-2022) that paid 0.55 BTC.
    – Demonstrated rapid weaponization of the ProxyNotShell POC within only three days of disclosure—highlight need for Emergency Patch sandboxes and blue-team playbooks that measure Mean Time-to-Patch against CVSS 9.x defects.

End of CommonRansom technical & recovery resource.