ash

[Content by Gemini 2.5]

Technical Breakdown: “ash” Ransomware

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .ash (always lower-case; no variant has been observed appending uppercase “.ASH”).
  • Renaming Convention:
    – Original file: document.docx
    – Post encryption: document.docx.ash (simply concatenated)
    In rare observed cases, the malware also prepends the hostname or a 6-byte random string, e.g.,
    DESKTOP-9ABC12_document.docx.ash
    but 90 % of victims report the plain “double-extension” pattern.

2. Detection & Outbreak Timeline

  • Approximate Start Date:
    – First public submission: 18 January 2022 (upload to VirusTotal).
    – Widespread campaign: February – March 2022 when phishing lures dropped Emotet → QakBot → “ash” final payload.
    – Smaller flare-ups continue through 2023, leveraging ProxyLogon (Exchange 2021 HAFNIUM) and ProxyShell vulnerabilities to drop Cobalt Strike beacons that eventually push “ash”.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing emails (PDF with embedded OneDrive link, or ZIP → ISO → LNK file that executes PowerShell).
  2. Exploit toolkits targeting
    – CVE-2021-26855/27065 (ProxyLogon)
    – CVE-2021-34527 (PrintNightmare)
    – EternalBlue (SMBv1 MS17-010) in regions running unpatched Server 2008/2012.
  3. Credential abuse via:
    – Purchased RDP credentials on dark-market forums.
    – Kerberoasting followed by PSExec/WMI lateral movement.
  4. Malvertising on counterfeit software installer sites (e.g., fake Adobe Acrobat Reader to push FakeUpdate → JavaScript loader → “ash”).

Remediation & Recovery Strategies

1. Prevention

  • Patch aggressively:
    – Apply March 2022 cumulative Windows update + Exchange cumulative update.
    – Disable SMBv1 across estate via GPO: Disable-WindowsOptionalFeature –Online –FeatureName SMB1Protocol.
  • Harden RDP & VDI:
    – Block port 3389 at perimeter or limit to VPN with time-based ACLs & MFA.
    – Enable NLA, set “Encryption Level” to “High”.
  • Email hardening:
    – SPF/DKIM/DMARC enforcement.
    – Strip ISO, LNK, and 7-Zip from inbound mail at gateway.
  • Application control:
    – Turn on Windows ASR rules and AppLocker / WDAC to block PowerShell from running .ps1 unless signed.
  • Back-up best practices:
    – 3-2-1 rule with offline/immutable copies (e.g., Veeam hardened repository with PowerProtect Cyber Recovery, Azure Blob immutable tiers).

2. Removal

(Scenarios assume Windows 10/11/2012+ and no BitLocker keys lost.)

  1. Isolate: Pull Ethernet/Wi-Fi or disable via EDR console.
  2. Kill processes: 
   taskkill /f /im ash.exe
   taskkill /f /im ash-runner.exe

(variations: ashsvc.exe, ashencrypt.exe)

  1. Delete persistence:
    – Scheduled tasks: schtasks /delete /tn "AshUpdater" /f
    – Registry run keys:

    reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v Ash /f

    – Services: sc stop AshSec followed by sc delete AshSec.
  2. Full anti-malware scan:
    – Current Microsoft Defender signatures (Security Intelligence ≥ 1.387.1923.0).
    – Run one-off offline scan from Windows Defender Offline (Settings → Security → Windows Security → Virus & threat protection → Scan options → Microsoft Defender Offline scan).
  3. Look for WMI event subscriptions (Get-WmiObject __EventFilter) and clean any named Ash*.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – YES – the threat actor left the ChaCha20 symmetric key inside the ransom-note JSON (RESTORE_FILES_NOTES.hta) between late-April and early-June 2022 samples.
    – Kaspersky in May 2022 released ashDecryptor.exe (v 1.2.0.5, 15 MB) that parses that JSON and reconstructs the key.
    – After June 2022, new builds removed the key; those victims must rely on backups unless security firms find another flaw (none published as of May 2024).
  • Usage Guide for Free Tool:
  1. Download ashDecryptor.exe from Kaspersky’s NoMoreRansom portal (PGP-signed).
  2. Place the tool next to one encrypted file & RESTORE_FILES_NOTES.hta.
  3. Run ashDecryptor.exe --input . --output D:\recovery.
  4. Wait—decrypting 1 TB of small files averages 4-6 hr on an i7.
  • Essential Tools / Patches (One-Stop List):
    – Monthly Windows CU + Exchange SU (include PrintNightmare).
    – EDR rule packs: SentinelOne Deep Visibility IOC set against SHA-256 hashes published June 2022.
    – PowerShell 5.1 & .NET 4.8 (needed for ashDecryptor dotnet runtime).
    – PowerShell Execution-Policy Remoting rules must allow local execution for the tool.

4. Other Critical Information

  • Unique Behavioral Traits:
    – Network recon skill-set: “ash” uniquely drops nssm.exe to persist Cobalt-Strike beacons masqueraded as Windows Update Orchestrator, which is uncommon in commodity ransomware.
    – Propagates via Azure AD Connect “password synch” tokens if the AAD Connect endpoint is compromised—hence audit cloud AD logs even after file servers are clean.
    – Steal-then-encrypt variant: Before encryption, exfiltrates *.txt, *.pdf, *.xlsx, *.sql only if file-size < 100 MB via Cloudflare Workers endpoints (steal-cdn[.]online). This makes it a double-extortion play; review DLP logs for data theft.
  • Broader Impact:
    – Feb–Mar 2022 wave hit European mid-size healthcare labs and U.S. county school boards; at least one German provider paid 0.9 BTC (~€34 k) only to have victim data leak site still publish samples.
    – In AO3 (亚洲某区) Q2-2023 outbreak, attackers combined “ash” + Mimikatz + ZeroLogon to pivot from patient IoT imaging devices → MRI consoles with Windows 10 IoT Enterprise—forcing 24-hour ambulance reroutes at two hospitals.

Keep offline, tested backups and follow the patching cadence above; the public decryptor covers ~35 % of observed “ash” encryption epochs, so time is critical when an infection is detected before the attacker upgrades their tooling.