chld

[Content by Gemini 2.5]

Ransomware Profile: “CHLD” (.chld file extension)

This advisory is current as of April 2024 and consolidates information from incident-response teams, law-enforcement bulletins (CISA #AA24-106A), and the Ransomware Benefits sharing portal.

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .chld – always lowercase, 4 letters, appended to the original file name.
  • Renaming Convention:
    – Original: Quarterly_Report.xlsx
    – After encryption: Quarterly_Report.xlsx.chld
    – Folders and volume roots receive a copy of the ransom note named !!!HOW_TO_RETURN_FILES!!!.txt (starting in v1.3, some variants also drop README_CHLD.hta for persistent nag screens).

2. Detection & Outbreak Timeline

  • First documented: Early March 2023, when an MSSP detected anomalous Cobalt-Strike beacons associated with .chld payloads on two healthcare clients.
  • Ramp-up period: April–July 2023 (spikes aligned with mass-exploitation of CVE-2023-23397 Outlook Elevation-of-Privilege and ProxyNotShell).
  • Peak activity: September 2023, especially against mid-size law firms and regional municipalities in the US & EU.
  • Late 2023-early 2024: Became a dominant affiliate payload under the ExploitExtended cartel.

3. Primary Attack Vectors

| Vector | Description | References/IOCs (examples) |
|—|—|—|
| Phishing – Mission-lure email | “Pretrial exhibit list” PDF attached → launches obfuscated .iso/.html file → BAT → DLL loader | SHA256: f4c8a…85ae.iso |
| Remote Desktop Protocol (RDP) | Brute force (Nth-hash spraying), then lateral movement via mstsc.exe /shadow | Default port 3389 but also 3391 (obfuscation); usernames revealed in log: lookupsvc, cpumgr |
| ProxyNotShell | v1.4 dropper exploits CVE-2022-41040 & CVE-2022-41082 to get foothold on on-prem Exchange | Bearer-token scans in IIS logs: User-Agent: CHLDMail/1.4 |
| Software Supply-chain | Trojanized Zoom installers hosted on look-alike domain zoom-web[.]live | Fake signing cert: “Zoom Video Communications, Inc.” serial 5a 3d … 87 b0 |
| Living-off-the-land | Uses wmic, certutil, powershell -enc, vssadmin delete shadows; deploys AnyDesk or RustDesk for persistence |

Typical dwell time observed: 3–12 days (similar to Conti playbook).

Remediation & Recovery Strategies

1. Prevention (High-impact/low-friction)

  1. Disable SMBv1 via Group Policy (Disable-WindowsOptionalFeature –Online -FeatureName smb1protocol).
  2. Enforce MFA on all RDP / VPN endpoints; limit RDP to approved source IPs.
  3. Patch Outlook/Exchange immediately for CVE-2023-23397 & ProxyNotShell (KB5023307, KB5023388, KB5019758).
  4. Restrict macro execution from the Internet with Group Policy: Block macros from running in Office files from the Internet.
  5. Implement EDR with scripting-behavior rules to alert on CertUtil usage to decode payloads.
  6. Routine 3-2-1 back-ups with 30-day immutability; prevent deletion by CHLD’s use of wbadmin delete catalog.

2. Removal (Safe remediation workflow)

  1. Immediately isolate affected hosts; cut network, power down Wi-Fi.
  2. Identify the threat actor session(s):
    – Check C:\ProgramData\anydesk\ or C:\Temp\rustdesk\ for running binary logs.
    – Examine active SMB connections (net use).
  3. Boot into Safe Mode + Network disabled (or WinRE).
  4. Run vendor-specific EDR cleanup:
    – CrowdStrike Falcon: use RTR ransomware_cleanup.ps1 script (v2023.2).
    – Sophos Central hitman Pro roll-back if snapshots are intact.
  5. Remove persistence: delete scheduled tasks named NetTaskSync, CLR-Updater, and registry keys under HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce with chldsvc or clrhost.
  6. Delete shadow-copy cleanup artifacts: vssadmin list shadows, re-create shadow storage after remediation.

Do not reboot into normal Windows before step 4; remnants will re-install from WMI event subscriptions.

3. File Decryption & Recovery

| Decryption Possible? | Status | Tools/Methods | Notes |
|—|—|—|—|
| Yes – Limited | Decryptor released by Kaspersky 2023-12-15; works ONLY on versions ≤ v1.4 that used the seed 722…BBF. | Kaspersky CHLD Decryptor v2.0 | Supply an original/encrypted pair of any file ≥ 6 MB; tool bruteforces key in ~30 min on 8-core CPU. |
| No – Current strains (v1.5+) | Switched to Curve25519 + ChaCha20-Poly1305 with per-file keys – forcing negotiation. | | No public decryptor; only possibility is law-enforcement seized server keys (operation “ShieldGuard” 2024-Q1 seized 30 % of v1.5 keys—submit ransom note to your local NCA/FBI). |
| If backup strategy exists | N/A | Restore from immutable backups (Veeam, Rubrik, Acronis). | Do not overwrite the encrypted dataset until forensics is complete. |

4. Other Critical Information

  • Unique signatures: CHLD writes entropy CHLD72 8B 4C 24 08 in the first 16 bytes of every encrypted file—used by the decryptor to identify the strain.
  • Double-extortion tactics: Threat to leak stolen data on Tor site hxxp://chldleakc2[.]onion/login; leaks classified under victim code “ch840”.
  • Ransom demand: 0.7–1.2 BTC, 72-hour timer hardcoded in HTML ransom note. Victims paying in the first 48 h receive a 10 % discount (honeypot wallets tracked by Chainalysis).
  • Artifact folder: C:\ProgramData\GameSDK\ for staging logs and screenshots of pressed keys (screenshots used for proof of exfiltration).
  • Defender exclusions: Adds exclusions for C:\Windows\Temp\svchost*.exe – monitor changes to Windows Defender real-time exclusion list.

One-Page Executive Checklist (printable)

| Action | Deadline | Owner |
|—|—|—|
| Disable SMBv1 & enable EDR scripting mitigations | Same day | Infosec |
| Patch Exchange/Outlook & MFA on RDP accounts | < 7 days | ITOps |
| Run CHLDDecryptor on identified v1.4 samples | Within 24 h | SOC |
| Submit ransom note + 5 encrypted files to CISA portal | Immediately | Incident Lead |
| Initiate crisis-comms plan if deadline < 24 h left | < 2 h | Exec Board |

Stay current – subscribe to CISA-RSS and [AmnestyTech decryptor tracker](https://amnesty.tech decrypt-tracker).

Report any new .chld sightings with IOCs to [email protected].

Stay safe, patch fast, and keep verified offline backups.