chch

[Content by Gemini 2.5]

Technical Breakdown – Ransomware Variant CHCH

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    CHCH (sometimes appended more than once or with an added random 4-character suffix, e.g., .demn or .bqtd).
    Example: Project2023.xlsx becomes Project2023.xlsx.CHCH.demn.

  • Renaming Convention:
    After the initial .CHCH, the ransomware often injects a second, campaign-specific 4-character extension (.tqny, .bqtd, .demn, .xyza, etc.). Inside every affected folder it drops a file named !CHCH_INFO!.rtf, ReadMe_CHCH.txt, or similar that contains the ransom demand. Some droppers also alter the volume label of logical drives to CHCH.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First telemetry hits were registered on 7 March 2023. Significant campaigns were seen in the wild through May–June 2023, with a resurgence in late October 2023 tied to new affiliate packs using the LockBit 3.0/BlackCat builder templates.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    1. Remote Desktop Protocol (RDP) compromise – Brute-force or credential-stuffing against exposed RDP (TCP/3389) followed by manual lateral movement.
    2. Exploitation of ProxyShell (CVE-2021-34473, CVE-2021-34523, CVE-2021-31207) and ProxyNotShell (CVE-2022-41040, CVE-2022-41082) on on-prem Exchange servers to drop the CHCH loader.
    3. Phishing – Emails with ISO or IMG attachments masquerading as invoices; once mounted, the image launches RuntimeBroker.exe (signed but side-loaded with malicious DLL).
    4. Software supply-chain incidents – A trojanised version of VLC 3.0.18 circulated on certain warez sites in Q2-2023; the illegitimate installer silently fetches and executes CHCH.
    5. Pre-existing Cobalt Strike beacons converted into CHCH dropper infrastructures.

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures
    • Patch immediately – Exchange, Windows SMB, Print Spooler, and third-party software (especially 7-Zip, VLC, Citrix ADC).
    • Disable SMBv1 (Disable-WindowsOptionalFeature ‑Online ‑FeatureName smb1protocol) everywhere.
    • Multi-factor authentication on RDP, VPN, and OWA portals.
    • Restrict inbound RDP to known jump hosts via firewall/VPN.
    • Application allow-listing (Applocker, Microsoft Defender ASR rules).
    • Network segmentation – isolate OT/IoT segments and prevent lateral SMB traffic.
    • Daily, offline or immutable backups (Veeam Hardened Repo, AWS S3 Object Lock, Azure Immutable Blob).

2. Removal

  • Infection Cleanup (Level-2/Level-3 incident response)
    1. Power-off and isolate the affected host(s) from the network; do not reboot—some variants schedule a delayed encryption pass after restart.
    2. Acquire forensic images of system volume before clean-up if legal obligations demand chain-of-custody.
    3. Boot from external media (Windows PE Kape, Bitdefender Rescue CD) to run AV/EDR scans; recommended engines: Microsoft Defender Offline, ESET Live, Bitdefender Rescue.
    4. Delete persistence artefacts:
      • Run keys – HKU\SID\...\Run → RuntimeBroker.exe, updater.exe
      • Scheduled tasks – \Microsoft\Windows\LanguageComponentsInstaller\Installer (name varies).
    5. Remove undiscovered lateral-movement tools: look for Rubeus.exe, Impacket wmiexec, and PowerShell WebClient usage in proxy logs.
    6. Verify completeness – Run a second scan from a different vendor and hit the network again only after zero detections for 24 h.

3. File Decryption & Recovery

  • Recovery Feasibility:
    At the time of writing, NO FREE DECRYPTOR exists for CHCH. The ransomware uses a hybrid cryptosystem: AES-256-CBC per-file keys encrypted by an RSA-2048 public key embedded in the loader. Victims with valid offline backups and no key leakage confirmed by Emsisoft labs in July 2023.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for CHCH – None released (2023-Q4). Subscribe to the Emsisoft blog for future updates.
    • Microsoft Defender KB5021304, KB5026361, KB5028185 – stop the ProxyNotShell exploit chain.
    • CrowdStrike CHCH YARA rules (community GitHub) for scanning RAM and shadow copies post-intrusion.

4. Other Critical Information

  • Unique Characteristics:
    • CHCH’s authors used the leaked BlackCat/ALPHV locker source to bolt on the double-extension naming convention.
    • Embedded WMI-based wiper logic – after a 21-day ransom deadline it attempts to corrupt Volume Shadow Copies again using vssadmin Resize ShadowStorage.
    • Fortinet FortiOS CVE-2022-42475 was included in at least one campaign for persistence on firewalls.

  • Broader Impact:
    • New Zealand Police (Christchurch region) and an Australian hospital group both disclosed CHCH attacks in July 2023, raising awareness that CHCH was not just another “off-the-shelf” strain but actively sought large enterprise payouts.
    • Chained with credential-marketplace infostealer “Raccoon Stealer v2” logs; rebuilding user identity trust after CHCH incidents is therefore critical.

Stay vigilant, patch aggressively, and keep immutable backups—you are still the last line of defence against CHCH.