cring

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The Cring ransomware appends the extension .cring to every encrypted file.
  • Renaming Convention: Files are renamed in the pattern
    <original name>.<original extension>.cring
    Example:
    Report.xlsx → Report.xlsx.cring
    tg4D2021.bak → tg4D2021.bak.cring

Note: If a victim’s machine is hit twice (double-extortion group re-using Cring or something pretends to be Cring), you may see longer chains such as .jpg.cring.cring; only the last .cring segment matters for accurate identification.

2. Detection & Outbreak Timeline

  • Discovery: Analysts first identified and publicly reported Cring ransomware in January 2021.
  • Peak Activity: February–April 2021 witnessed the largest waves, especially across IT service providers, manufacturing, and municipal networks in Europe.
  • Ebb & Flow: While large-volume campaigns subsided mid-2021, Cring binaries are still reused by affiliates in 2022–2023 dropper chains and by opportunistic actors leveraging fresh leaks of Cobalt-Strike beacons.

3. Primary Attack Vectors

| Vector | Details & Exploits Employed |
|——–|—————————–|
| Log4Shell (CVE-2021-44228) | The group almost immediately weaponized Log4Shell against publicly-exposed Apache web services (vSphere Center, bespoke web consoles) to harvest credentials and establish footholds. |
| Remote Desktop (RDP/SSH brute-force) | Cring’s post-ex lateral movement often starts from an RDP port (3389) left exposed to the Internet. |
| Fortinet VPN (CVE-2018-13379, CVE-2020-12812, CVE-2020-15510) | Multiple publicly available PoCs allowed Cring actors to dump plaintext VPN credentials, pivot, and launch ransomware executables inside the trusted LAN segment. |
| SMB | EternalBlue / DoublePulsar | Outdated Windows 7 / Server 2008 R2 boxes lacking MS17-010 patches were pulled into the kill-chain, enabling the malware to create scheduled tasks on hosts it could not log into directly. |
| Malicious email missed by gateway | Phishing emails with ISO/IMG attachments (zero-byte AVI stubs, LNK guised as PDFs) were observed in early spring 2021. Closing the initial vector does not help if attackers compromise domain admin later via RCE on a public asset. |

Remediation & Recovery Strategies

1. Prevention

  • Immediate Patching Priorities:
    – FortiOS/FortiProxy (check for the three above CVEs; apply vendor firmware or disable SSL-VPN role).
    – Apache Log4j2 to 2.17.1 or later.
    – Windows / Server 2012–2022 (enable automatic updates and validate MS17-010 status via wmic).

  • Network Hardening:
    – No direct Internet-exposed RDP. Use VPN without split-tunnel and combine with MFA.
    – Disable SMBv1 across the estate (Set-SmbServerConfiguration -EnableSMB1Protocol $false).

  • Privileged Access Hardening:
    – Mandatory EDR + MFA on domain admin accounts.
    – Least-privilege: separate Tier 0 / Tier 1 / Tier 2 admin accounts.

  • Back-Up Strategy:
    – 3-2-1 rule (three copies, two media, one off-line/off-site).
    – Daily immutable cloud backups (test restore quarterly).
    – Store Veeam backups on Linux repositories with hardened repository feature (chattr +i).

2. Removal

  1. Containment
  • Physically or logically isolate affected hosts (pull power or block at switch).
  • Power down any VM snapshots created before detection; ransomware deletes .vmdk backups via wevtutil.exe cl Application.
  1. Forensics & Logging
  • Capture disk images (Guymager or Kape triage) for incident-response vendors.
  • Save Windows event logs (wevtutil epl if the service is still running).
  1. Malware Eradication
  • Boot from a trusted WinPE/Ubuntu LiveUSB → delete the following persistencies:
    • C:\Windows\System32\Tasks\NameFromRansomnote (scheduled task).
    • Registry Run keys under HKLM\Software\Microsoft\Windows\CurrentVersion\Run.
  • Remove lateral-movement tools: PsExec.exe, Rubeus.exe, svchosts.exe (C2-named binaries), Cobalt-Strike beacon DLLs found under %windir%, %userprofile%\.config, or ProgramData.
  1. GPO & Service Restoration
  • Re-enable Windows Defender real-time protection (group-policy overrides may have turned it off).
  • Reset AD account passwords for all OUs that were touched; verify password-policy length is at least 15 chars.

3. File Decryption & Recovery

  • Free Decryptor? No – Cring uses AES-256+RSA-1024 with unique keys per machine. The private RSA key remains on actor-controlled servers.
  • Recovery Only via Backup: Restore from the last verified and clean backup.
    • Test a small folder first, then full volume.
    • If immutable backups (e.g., Wasabi S3 with Object Lock) are intact, rotation will be asymmetric and ransomware cannot touch them.
  • Shadow Copy Alternative: Modern Cring variants now run vssadmin delete shadows /all. If you are lucky, Volume Shadow Services may still contain pre-attack snapshots that can be mounted with diskshadow under WinPE.

4. Other Critical Information

  • Potential Double Extortion: Cring actors exfiltrate files with rclone to the Mega sync client; filenames appear in ransom note under “STOLEN DATA SECTION.” Objectives often include sector compliance data (GDPR/SOX), so consider breach notification obligations even after recovery.

  • Ransom Note Location & Name:

  • !RECOVER-FILES!.txt (placed in every encrypted folder) contains a Tox chat ID and unique Victim-UID.

  • The actor demands 0.5–2 BTC but negotiations are rare; they typically ignore victims after first contact.

  • Unique IOC Signatures:

  • Mutex: CringMutex201654

  • SHA256 (blue-team hunters look for): 1d63bdb8b2d03c61c56a1a0635a54e177e107e7e6e2f1cc2c68af292442ebe31

By combining the above hardening practices (patch, backup, MFA) and the explicit IOCs/Mutex identifiers, an organization can confidently detect, contain, and remediate Cring ransomware without paying the ransom.