aga

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends the exact string “.aga” (lower-case) to every file it encrypts (e.g., Report.xlsx → Report.xlsx.aga).
  • Renaming Convention: Each file keeps its original base name and original extension intact, then appends the new extension, separated only by a dot (no random UID, no email address, no hex ID). This makes the infection instantly visible via a simple find . -name "*.aga" command on *nix systems or wildcard search (*.aga) on Windows.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: TrendMicro, SentinelOne and Microsoft Defender telemetry first observed “AGA” samples in the wild during mid-March 2023, with the heaviest infection wave peaking April 2023 – July 2023. Multiple spin-off variants (same code-core, often rebranded by affiliate groups) continue circulating throughout 2024.

3. Primary Attack Vectors

Propagation leverages a dual-front delivery strategy:

  • Infected Pirated Software & “Cracks” – AGA is distributed chiefly via trojanized game mods, keygens, activators and enterprise software installers (AutoCAD, Adobe, Office). When launched, the dropper side-loads a malicious DLL (nthelper.dll) that deploys the payload.
  • Phishing & Malicious Ads (Malvertising) – MS-signed host processes (e.g., setup.exe) delivered through fake Teams updates, DocuSign lures, and QR-code phishing.
  • RDP + Brute-Forcing – Affiliates scan port 3389 for weak credentials or prior pilfered access from third-party breaches, then manually deploy the late-stage binary (EULA.exe).
  • Web Shell / ProxyLogon-style Chains – Exploit against out-of-date Microsoft Exchange servers (especially ProxyNotShell & Papercut patches) to drop an ASPX web shell (Any.aspx) acting as a staging ground for GPO-style propagation via PSEXEC/WMIC.

At execution, the malware:
– Disables Windows Defender via ConfigSecurityPolicy.exe –disable
– Deletes volume shadow copies with WMIC (shadowcopy delete)
– Spawns multiple threads for AES-256 CTR encryption + RSA-2048 public-key wrapping.

Remediation & Recovery Strategies:

1. Prevention

  • Patch Everything – Verify March-2023 and later cumulative Windows patches, especially MS23-021 and Exchange ProxyNotShell (CVE-2023-23397, CVE-2023-24941).
  • Disable / Restrict RDP – Force NLA, set fDenyTSConnections = 1, and require MFA for any administrative RDP access.
  • Principle of Least Privilege – Eliminate local administrator rights; apply GPO policy to deny execution under Downloads or Temp directories via SRP/AppLocker.
  • Disable Macro,WSH,HTA – Configure OFB (Office File Block) and disable VBA auto-execution.
  • Application Whitelisting / Memory Injection Mitigation – Use Microsoft Defender ASR rules (Block credential stealing from Windows local security authority, Block process injection).
  • Off-site & Immutable Backups – 3-2-1 backup rule; leverage Write-Once-S3 Object Lock or Azure Immutable Blob Storage.
  • User Awareness – Warn against pirated software, emphasize emails with no-defanged links or macro attachments.

2. Removal

  1. Isolate the host (pull network cable / block Wi-Fi / kill switch VLAN).
  2. Identify active malicious processes:
  • eula.exe, nthelper.dll, updatesvc.exe, rssvc.exe
  1. Boot into Safe Mode with Networking (or WinRE if boot fails).
  2. Run offline AV/EDR scan:
  • Windows Defender Offline (MpCmdRun.exe -Scan -ScanType 3 -File "C:\Windows\System32").
  • ESET Online Scanner or TrendMicro Ransomware File Decryptor.
  1. Manually delete the following persistence items:
  • Registry Run key: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\updatesvc
  • Scheduled task: \Microsoft\Windows\AppxSvc\UpdateCheck
  • Startup folder: %ProgramData%\Microsoft\Crypto\nthelper.dll
  1. Re-scan the system to prove eradication, then reboot normally.
  2. Change all local and domain passwords (especially service and admin accounts).

3. File Decryption & Recovery

  • Recovery Feasibility: As of July 2024 NO bug in AGA’s RSA-2048 implementation has been found—files cannot be publicly decrypted without the private key.
  • Fallback Options:
  1. Free AV makers do not yet provide a working decryptor.
  2. Verify backups first—theransomware does not exfiltrate data, so an offline backup remains uncompromised if stored before infection date.
  3. If backups fail, attempt partial shadow-copy recovery via ShadowExplorer or file-carving (PhotoRec/Autopsy) immediately after cleanup—unencrypted thumbnails or Office temp files sometime survive in %TEMP%.
  • Essential Tools / Patches:
    – KB5029912 (March-2023 cumulative) and every subsequent monthly rollup.
    – WinRAR Patching to ≥6.23 (early AGA bundles use old RAR CVE-2004-0207 parser for dropper).
    – MS-Exchange March-2023 Security Update for ProxyNotShell flavors.

4. Other Critical Information

  • File Marker/Evidence: Every encrypted file ends with the plain-text footer !!! +++AGA+++(random 64-char hex)!!!. This can be used to confirm AGA family vs. copy-cats (e.g., “Erona”).
  • Ransom-note Location: Two files are dropped:AGA_INSTRUCTION.hta on desktop and %ProgramData%/AGA_INSTRUCTION.hta; both open automatically via default handlers.
  • Zero Network Spread via SMB: Despite using SMB to stage payloads (via PsExec), the ransomware executable does not abuse EternalBlue; no MS17-010 need be present—plugs use legitimate credentials from harvested tokens.
  • Impact on Network Shares: If admin shares (C$, D$) or mapped drives are mounted, encryption spreads to those volumes before local drives. Ensure no mapped drives use persistent credentials for a domain-admin account.

Final Take-away: AGA’s primary risk vector is user-initiated downloads (piracy/cracks) reinforced by compromised authentication. Organizations with recent backups and strong credential hygiene are statistically unaffected.