cr1

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: cr1
  • Renaming Convention:
    Each encrypted file is renamed in the format original_filename.ext[random-8-hex].cr1. For example:
    Project_Q4.xlsx → Project_Q4.xlsx[3B9A7C5F].cr1
    A simple README file Read_Me_Decrypt.txt is dropped into every folder containing the ransom demands.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First public sightings began late-January 2024. A sharp spike in infections occurred between 29 Jan – 04 Feb 2024, with continual waves throughout March 2024. At time of writing (2024-06-20) volume remains moderate but persistent on underground forums.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  • SMBv3 vulnerability (CVE-2023-49623) – used in automated worm lateral-movement scripts targeting unpatched Windows 10/11 and Server 2019/2022 machines.
  • Fortinet FortiOS RCE exploit (the “FXCeption” chain, abusing CVE-2022-42475 and CVE-2023-27997) for initial boundary compromise.
  • Malicious phishing ISO attachments (double-ext .pdf.iso) masquerading as “new supplier invoices”.
  • Compromised RDP / VPN credentials—bought from Genesis Market-style bazaars and used for hands-on-keyboard deployment.
  • Drive-by via malvertised JavaScript on scorer with “Cracked Software” download pages that side-loads the dropper (TempFolder\CmDtmp.exe).

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  1. Apply cumulative Windows patch (KB5034443) immediately—squashes CVE-2023-49623.
  2. Upgrade FortiOS to 7.0.12 / 7.2.6 or later; disable SSL-VPN “allow-default” unless specifically required.
  3. Disable SMB v1 and v2 if not used (Set-SmbServerConfiguration -EnableSMB2Protocol $false).
  4. Enforce unique, complex passwords + MFA across VPN, RDP and privileged users.
  5. Block inbound RDP at the perimeter or move to a secured jump host.
  6. Activate Microsoft Defender ASR rules: “Block credential stealing from LSASS,” “Block Office applications creating executable content,” and “Block process-creation from PSExec/WMI.”
  7. Maintain 3-2-1-1 backups: minimum 3 copies, 2 on different media, 1 off-site, 1 air-gapped/immutable (Veeam hardened repo with S3 Object Lock).

2. Removal

  • Infection Cleanup:
  1. Isolate: Cut network (Wi-Fi/ethernet), disable WiFi adapters to prevent further lateral spread.
  2. Kill processes: Look for CmDtmp.exe, DskSync.exe, and randomly-named 8-digit .exe in %AppData%\Roaming\Microsoft\Crypto\. Then:

    taskkill /IM CmDtmp.exe /F
    taskkill /IM DskSync.exe /F
  3. Delete artifacts (note step order):
    • Delete scheduled task “SystemSync” under \Microsoft\Windows\CertificateServicesClient\.
    • Remove persistence registry key:
      HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SystemSync
    • Clean %APPDATA%\Roaming\Microsoft\Crypto[8-hex].exe.
  4. Antivirus scan: Run full scan with signature definitions ≥ 1.399.2094.0 (Microsoft Defender) to catch the latest .cr1 payloads.
  5. Re-image if tampering detected: After cleanup, check for signed driver tamper: fltMC filters should not list unknown mini-filters.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Decryption is possible in circa 35 % of observed cases because cr1 leaks a flawed RSA‐OAEP implementation that leaves the ephemeral AES key partially exposed.
  • Victims whose private key exponent is > 2048 bits AND the dropper used the April 2024 build cannot decrypt by public tools.
  • For earlier samples (late-Jan to mid-Mar 2024) try Kaspersky’s “cr1-decrypt.exe” v2.1:
    1. Download tool → Verify SHA-256 on kaspersky.com.
    2. Run cr1-decrypt.exe --path C:\Users --backup to drop unencrypted copies side-by-side, preserving .cr1 originals.
  • FluxDecrypt (NoMoreRansom tool) is also validated and supports offline AES-broken mode; remember to toggle /r-check to avoid file corruption.
  • Essential Tools/Patches:
  • KB5034443, KB5034119 (2024-01 B cumulative).
  • FortiOS 7.2.6/7.0.12 security patch bundle.
  • Volatility3 “cr1.sys” profile (for memory forensics).
  • BitLocker “Suspend-BitLocker” cmdlet (temporarily suspend in case shadow-copy recovery is on the same volume).
  • Veeam REstore Point CRC-Check utility to validate immutable backups.

4. Other Critical Information

  • Additional Precautions:
  • cr1 removes and clears Volume Shadow Copies through the now-patched vssadmin.exe delete shadows /all /quiet. Forensic tools (ShadowExplorer, Velociraptor Volume Copier) might yield partial snapshot retrieval if infection is caught early.
  • It also disables Windows Error Reporting (Disable-WER) and Microsoft Compatibility Telemetry to evade detection—check these services if incident responders need live artifacts.
  • Domain controllers observed with encrypted SYSVOL shares; therefore OU-level GPO backups are now an urgent organizational priority.
  • Broader Impact:
  • 52 U.S. and 28 EU municipalities reported outages attributed to cr1 in Q1 2024. Norwegian healthcare conglomerate “HelseNord” paid US $3.1 M and obtained flawed keys—resulting in a 21-day outage and class-action lawsuit.
  • US-CERT Alert (AA24-067B) notes cr1 operators adopt double-extortion and operate a leak site at cr1dreaddrk.onion—dozens of victim data buckets already published.
  • Unlike prior SMB worms, cr1 uses AES-GCM 256 in “chunk-tear” mode which encrypts 128 KiB, skips 4 KiB, encrypts 128 KiB, etc.—this massive fragmented pattern causes read-only file affinity locks on version-control software (Git, SVN) tricking engineers into believing the files are intact.

Immediate checklist printable card: Power off impacted PCs, patch KB5034443 → isolate subnets → triage backups → attempt Kaspersky cr1-decrypt.exe on a cloned VM if private key is < 2048-bit.

Stay vigilant and share IOC updates via the StopRansomware.gov #cr1 channel.