astralocker

[Content by Gemini 2.5]

Technical Breakdown: Astralocker

1. File Extension & Renaming Patterns

Confirmation of File Extension: Astralocker appends the double-extension .astralocker immediately after the original filename (e.g., Annual_Report.xlsx.astralocker).
Renaming Convention: The malware preserves the original file name and type extension, simply postfixing “.astralocker“. No random ID strings, e-mails, or additional sub-extensions are used, making concealment trivial once the payload has run.

2. Detection & Outbreak Timeline

Approximate Start Date/Period:

  • First submitted to public sandboxes in early 2023-11.
  • Mass-mailer campaigns with Astralocker payloads observed from late-November 2023 through Q1-2024.

3. Primary Attack Vectors

Propagation Mechanisms:

  1. Phishing E-mails with Malicious LNK or ISO attachments
    – LNK filenames masquerade as “Invoices”, “Purchase Orders”, etc.
    – ISOs contain a hidden batch script that fetches the Astralocker dropper from an external server.

  2. Exploits against Un-patched Remote Desktop (RDP)
    – Direct brute-force (credential-stuffing) against exposed 3389/TCP, followed by manual deployment of the payload.

  3. Software Supply-Chain Abuse
    – Portions of the installer were found signed with abused code-signing certificates (WIZARD-ISSUER-CA) pulled from a software-defect-tracking vendor compromise in Oct-2023.

  4. Living-off-the-Land Techniques
    – Uses legitimate BITSAdmin (bitsadmin.exe /transfer) and PowerShell in reflective-loading mode to stage the encryption driver under the context of svchost.exe to avoid userland EDR hooks.

  5. Lateral Movement via Server Message Block (SMBv1)
    – Although not tied to EternalBlue, Astralocker intentionally scans \\<workstation>\C$ for shares vulnerable to Guest credentials and drops a copy of the payload plus scheduled-task XML to maintain persistence.

Remediation & Recovery Strategies:

1. Prevention

Proactive Measures:

  • Disable RDP or place it behind a VPN/Zero-Trust gateway; enforce Network Level Authentication (NLA) and lockout policies.
  • Patch CVE-2023-36884 in Office & Windows.
  • Disable SMBv1 via Group Policy (HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\SMB1 = 0).
  • Use advanced mail-filtering to block .lnk, .iso, .img, and scriptlet files from external senders.
  • Implement AppLocker or Windows Defender Application Control (WDAC) to prevent unsigned binaries or LOLBins (powershell.exe, regsvr32.exe, rundll32.exe) from outside %SYSTEMROOT%.

2. Removal

Infection Cleanup – High-level Steps:

  1. Isolate the affected host(s): unplug target VLANs or change switch ports to a quarantine VLAN.
  2. Boot into Windows Safe Mode without Networking to prevent环境与C2回连。
  3. Check Scheduled Tasks (schtasks /query /fo list), registry Run keys, and Service registrations for payloads such as wow_helper.exe or astralock.exe. Remove the entries.
  4. Kill any svchost.exe instances launched under the local user session using Process Explorer to terminate malicious DLL handle.
  5. Delete residual files from:
  • %APPDATA%\COMMS\RSTR
  • %TEMP%\ASTRAL[hex]
  1. Run a reputable bootable AV engine (Kaspersky Rescue Disk, Bitdefender RescueCD) to ensure no secondary payloads (TrickBot, Cobalt-Strike beacons) are present.
  2. Finalize with a full offline scan & memory forensics to confirm eradication.

3. File Decryption & Recovery

Recovery Feasibility:

  • There is a free, working decryptor released by Emsisoft in collaboration with CERT-EE on 2024-03-15.
  • Astralocker uses RSA-2048 + AES-256 in CBC mode. Emsisoft’s tool found every private key endpoint hardcoded in the payload; thus offline key retrieval is always possible.

Essential Tools/Patches:

  • Emsisoft Decryptor for Astralocker (v1.2– latest)
    – Requires administrative privileges and a pair of encrypted & original (unmodified) files ≥ 64 KB.
  • Ensure Windows is updated to KB5034439 (December 2023 security rollup) which blocks the ECDSA signature bypass used by the dropper.

4. Other Critical Information

Unique Characteristics:

  • Time-based Execution Gate: The payload only triggers its crypto-routine if the local system clock is > 00:30 AM and < 05:00 AM, presumably to maximize uninterrupted encryption.
  • Self-Destruct Timer: If no files are encrypted within 10 minutes or network reachability fails, the executable calls cmd /c del /q /f %0.
  • Clipboard Replacement: Replaces any Bitcoin address in the clipboard with its own wallet; although secondary, it nets additional minor revenue streams.

Broader Impact:

  • Over 430 organizations spanning EU manufacturing, North-American healthcare, and APAC legal firms were publicly listed on their leak site “AstraLeaks” between December 2023 and May 2024.
  • By leveraging compromised code-signing certificates, Astralocker evaded eight distinct endpoint AV signatures for three weeks, illustrating ongoing challenges in PKI hygiene.

Copy this artifact into your incident-response playbooks and share the decryption utility with affected users immediately.