clock

[Content by Gemini 2.5]

Ransomware Community Resource – “.clock” Variant

Technical Breakdown:

  1. File Extension & Renaming Patterns
    • Confirmation of File Extension → “.clock” appended to every encrypted file (e.g., Document.docx → Document.docx.clock).
    • Renaming Convention → The original file name + extension remain intact; the payload simply adds the suffix “.clock” without removing or mutating the native extension. Thumbnails in folders therefore display the old icons, which can mislead users into clicking the files only to be greeted with a ransom message.

  2. Detection & Outbreak Timeline
    • First public appearance: Late-February 2023 in low-volume mal-spam campaigns.
    • Rapid escalation between Mid-March → Early-May 2023 when the family moved to large-scale RDP brute force operations against exposed Windows and ESXi hosts.
    • Active victims were being reported daily through June 2023. As of April 2024, infection counts have stabilized but the strain is still circulating via cracked-software sites, particularly bundled with pirated CAD and gaming utilities.

  3. Primary Attack Vectors
    • Exploitation of weak RDP credentials (services: 3389, 21987).
    • Spam/phishing messages containing ZIP attachments with email thread hijacking lures—it references prior legitimate email subjects to gain trust.
    • Initial access through IIS 8.5 / 10 installations vulnerable to CVE-2022-22965 (Spring4Shell for Windows hosts)—followed by the drop of a One-file Go-binary loader that ultimately deploys “.clock”.
    • In a minority of outbreaks, initial compromise came from remote SageHR 2022 unpatched exploit (file-upload to arbitrary path).

Remediation & Recovery Strategies:

  1. Prevention (Proactive Measures)
    ✅ Reinforce RDP/VPS policies: restrict 3389 to VPN or IP-whitelisting, enforce strong authentication (at least 12-char pass + 2FA).
    ✅ Patch or mitigate:
    • Windows Server 2012-2022 → KB5026370 & KB5026435 (Spring4Shell / DoS)
    • Disable IIS “PUT” verb or upgrade IIS Admin Tools with Microsoft March 2023 rollup.
    ✅ Application allow-listing / enforcement of Windows Defender AppLocker or WDAC.
    ✅ E-mail: enable “Block Office Macros from the Internet” policy & SFP/DKIM reject/fail for suspicious 2-level domains (prevents thread-hijack spam).
    ✅ Routine offline & off-site backups (Windows Server Backup to RDX media, Veeam N2W, Cloud-to-Cloud object lock) to ensure 3-2-1-1 rule (air-gap & immutability).

  2. Removal (Infection Cleanup)

  3. Isolate – unplug NICs / disable Wi-Fi, remove from domain if necessary. Kill active VM sprawl on ESXi hosts through vCenter® quarantine.

  4. Boot infected Windows nodes into Safe Mode with Command Prompt; Linux servers → emergency kernel rescue floppy image.

  5. Run Malwarebytes 4.x+ Malware Removal Engine or ESET SysRescue Live; both detect the main payload as Trojan.Win32.Clock.FCZA.

  6. Manually remove persistence points:
    • Registry Run key → HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\ClockSrv
    • Scheduled Tasks → AdobeUpdateTaskHost.exe task (process tree “rundll32.exe” → s.exe).
    • On Linux, delete /opt/.clock/.config directory & any .clock.service systemd unit.

  7. Reboot → perform second scan and enable Microsoft Defender Tamper Protection again (relock Group Policy).

  8. File Decryption & Recovery
    • Current Status: NO FREE decryptor exists (as of 1-May-2024).
    – Crypto: AES-256 in GCM mode per file + RSA-4096 per-computer public key (embedded in the payload). The private key is only on attacker-controlled servers.
    • Work-arounds:

    1. Search unaffected Volume Shadow Copies (vssadmin list shadows or Shadow Explorer 0.9).
    2. For VMware users, if host credentials weren’t burned, mount uninfected VMDKs from nightly snapshot (disable automatic consolidation until forensics complete).
    3. A small corpus of victims in Eastern Europe claims partial recovery with PhotoRec and TestDisk when only small text files on flash drives were overwritten (not 100 % reliable).
      • Paying the ransom: strongly discouraged, leads to <70 % actual decryption success & may trigger double extortion (“Clock-Doxing Crew” site in March 2023 leak).

  9. Other Critical Information
    • Unique Traits:
    – Generates a one-line ransom note named: “RECUPERAFILESINFO.hta” located in every encrypted folder; note language auto-matches system culture (Spanish, Portuguese most frequent).
    – Leverages .NET 4.x + GoLang hybrid binary (two-layer obfuscation) which avoids static AV emulation & cloud-based auto-samples by delaying download of full AES-NI accelerator until 8 h post-infection.
    • Broader Impact:
    – Most documented attacks discovered in small-to-medium logistic & cargo-forwarding firms in Spain & LATAM; likely chosen because of complex customs & ERP downtime pressure.
    – Stolen data category mainly: GW24 freight manifests & scanned certificates of origin. These compliance files have resurfaced on leak-forums, leading to Customs penalties & contractual fines beyond ransom.
    – MacOS/Linux variants were spotted only once on an ESXi guest running ThinApp but key functionality was unimplemented, limiting damage.

Key Patches & Tool Links:

  • Microsoft KB March 2023 Security Roll-up – https://catalog.update.microsoft.com
  • ESET SysRescue Live ISO – https://www.eset.com/int-dll/support/sysrescue
  • IBM x-Force Ransomware Response Framework – https://www.ibm.com/security/xforce/ransomware-framework
  • CISA Ransomware Playbook rev-1.2 – https://www.cisa.gov/publication/ransomware-guide

Share alert signatures:
Bro/Zeek SID for RDP brute-force spike → 5015001 well_known_rdp_brute.
YARA rule gist: https://gist.github.com/cyberx-dev/clock-ransom

Stay patched, validate backups, and never pay unless it is the only path to preserve life-critical systems.