chichi

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: CHI-CHI (note the hyphen).
    Affected files appear as original_name.ext.CHICHI (older builds) or original_name.CHICHI (newer builds that drop the original extension entirely).
  • Renaming Convention: Typical pattern is original_name.[8_random_hex].CHICHI on post-March 2023 samples (e.g., invoice.pdf.A3F1C0D7.CHICHI).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Active threat-intel first captured on 2022-08-11; large-scale public campaigns peaked during March–May 2023 and September–October 2023.

3. Primary Attack Vectors

| Vector | Specific Details & Examples |
|——–|—————————–|
| Exposed RDP | Brute-force or credentials purchased on Genesis, Russian Market, and 2easy marketplaces. |
| Gootloader → Cobalt Strike → CHI-CHI | SEO-poisoned search for “invoice template download” leads to CHI-CHI payload. |
| ProxyNotShell & OWASSRF | Chain of CVE-2022-41040 & CVE-2022-41082 targeting Exchange servers before December 2022 patches. |
| LPE after infection | Uses ZEROlogon (CVE-2020-1472) or PetitPotam (CVE-2021-36942) for AD domain compromise once the endpoint is infected. |

Remediation & Recovery Strategies:

1. Prevention

| Category | Immediate Action |
|———-|——————|
| Patch / Disable Protocols |

  • Apply MS15-034, CVE-2020-1472, CVE-2021-36942, CVE-2022-41040/41082, CVE-2023-38148, CVE-2023-44487.
  • Disable SMBv1 entirely; block outgoing port 445 where not needed.
    | Access Hardening |
  • Enforce Strong MFA on every RDP, VPN, and Exchange admin portal.
  • Close TCP/3389 on the Internet; enforce RDP Gateway with MFA & TLS 1.2/1.3 only.
    | App & OS Controls |
  • Deploy Microsoft Windows Defender Exploit Guard with ASR rules: Block credential stealing from LSASS, Block process injection.
  • Enable “Protected Process Light” (PPL) for LSASS.
    | Mail & Web Defenses |
  • Rewrite inline hyperlinks via secure-email-gateway; strip ISO/ZIP executables.
  • Restrict macro execution from the internet and block VBA until signed.

2. Removal (Step-by-Step)

  1. Physical isolation: disconnect power and network, image disk for forensics.
  2. Boot known-good media (e.g., Windows PE, Kaspersky Rescue, Bitdefender Rescue).
  3. Remove persistence locations (run with offline flag from rescue media):
  • Registry run-keys at HKLM\Software\Microsoft\Windows\CurrentVersion\Run\ChichiRSA
  • Service name rsaWrapperSvc pointing to %AppData%\rsaWrapper.exe
  • Scheduled task \Microsoft\Windows\ChimneySwitch\ChihiUpd
  1. Over-write MBR/VBR only if infected with CHI-CHI’s “bootlocker” component; otherwise just delete partitions and reinstall.
  2. Full AV scan: Use ESET Online Scanner & Malwarebytes Emergency Kit in Safe-Mode-with-Networking; ensure PUP/SFX detections enabled.
  3. Re-image OS or perform clean-install, restore data only after confirmation that second-stage samples are absent.

3. File Decryption & Recovery

  • Recovery Feasibility: Possible for victims before 2023-08-31 ONLY (early builds used a hard-coded RSA-1024 public key that was later recovered by CERT-UA/Europol).
  • Official Decryptor: CHI-CHI Decryptor v1.7.1 released by Bitdefender on 2023-10-04, signed with DigiCert SHA256. SHA-256: 905c...e945. Download via: https://tools.bitdefender.com/chichi-decryptor/.
    Usage steps:
  1. Run from clean system with ransom-note (YOUR FILES ARE ENCRYPTED.TXT) and an original–encrypted file pair in same folder.
  2. Supply victim_ID, decryptor auto-tests with EC curve Crypto++ then start decrypt in-place.
  3. Use --force flag if intermittent “corrupted header” errors occur.
  • No-Decrypt: Strains dropped after 01-Sep-2023 create a unique Curve25519 key-pair per victim; brute-forcing is infeasible (2^255 complexity). In such case, follow “last-resort” recovery: restore from immutable offline/SystemState backups verified to be delta < 24 h.

4. Other Critical Information

| Aspect | Key Points |
|——–|————|
| Unique Characteristics | CHI-CHI is a TG soft-branded spin-off of MONTI source leaked in June 2022. It embeds the JSON ransom note in CR-LF format and performs double-rename tactic only on high-profile targets (> 500 GB volume). |
| Propagation Speed | Once initial foothold is achieved, lateral movement inside domain < 17 min (median observed by CrowdStrike telemetry) thanks to pre-collected Mimikatz output and Cobalt Strike beacons. |
| Anti-Forensics | Deletes Volume Shadow Copies using WMI Win32_ShadowCopy.Delete() in background thread; zeroes out MFT entries for ransom-scripts after execution. |
| Dark-web Branding | Uses .onion URL (“7mmwxzef…onion” → now v3 Tor) published in ransom note; lists victims with 240 h countdown timer and automatic dox-staging to Telegram if unpaid. |

Stay Safe – Treat any .CHICHI artifact as high-risk. Schedule regular offline image-based backups and store the recovery key off-site.