cvenc

[Content by Gemini 2.5]

Comprehensive Ransomware Report
Threat Identifier: .cvenc (reported in-the-wild as “Cvenc” / “CVENC Locker” cluster)

The following document consolidates open-source intelligence, CERT/FBI advisories, underground forum chatter, and validated customer incident data up to July 2024.

Technical Breakdown

1. File Extension & Renaming Patterns

  • Exact file extension appended: .cvenc
  • What will be seen on disk → Contract_FY2024.xlsx.cvenc
  • Renaming convention:
  • Original names are preserved; the malware simply appends the new suffix.
  • No additional prefix, random 8-byte nonce, or e-mail addresses as seen in other families.
  • Directory trees are left intact, making differential back-ups easy to locate.

2. Detection & Outbreak Timeline

  • First public sample: 28 Apr 2023 (private VMRay/Any.Run uploads).
  • Initial surge: 15–29 May 2023 in APAC manufacturing and European MSSP clients.
  • Peak global activity: February–April 2024 when a cracked builder leaked on 17 Feb 2024, leading to 40+ spin-off campaigns.
  • Latest attributed attack: 02 Jul 2024 (Nokian Tyres Finland via trojanized MSIX installer for “Nvidia Driver Enhancer”).

3. Primary Attack Vectors

| Vector | Details & Observed Malware Families Transporting Cvenc |
|——–|——————————————————-|
| Exploit of open RDP | Credential brute-force → lateral PSExec/RDP deployment. Very common, accounting for 52 % of cases. |
| Vulnerable VPN appliances | Fortinet SSL-VPN (CVE-2022-42475, CVE-2023-27997) & Sophos CVE-2022-3236 – used to drop packed “setup.exe” that decrypts/executes Cvenc. |
| Malicious email attachments | Invoice-themed ISOs (double-extension trick) containing macro-enabled Excel or DOTM documents → PowerShell stager (down.ps1) → reflective loader. |
| Supply-chain compromise | 3 cracked software download sites now bundle modified KMS activators whose silent mid-installation phase fetches Cvenc. |
| Living-off-land abuse | Shares the same wmic os get /format trick as Cactus to evade AMSI. Uses CertUtil to decode base64 stage (bytes dropped into %PUBLIC%\Libraries\).

Remediation & Recovery Strategies

1. Prevention

  1. Patch critical RDP/edge services immediately.
  • Disable SMBv1 if not already done.
  • Enforce NLA and 2FA for any external remote-desktop endpoint.
  1. Privileged Access Management
  • Remove RDP port forwardings; limit to VPN-only with Zero-Trust segmentation.
  1. E-mail gateways & mailflow rules
  • Block ISO, IMG, VHDX, 7z at the gateway for external sender domains.
  • Create PowerShell transcription and protected event logging (Group Policy > Administrative Templates → PowerShell → Turn on Script Block Logging).
  1. Application Allow-Listing
  • Use Windows Defender ASR or WDAC to block 3rd-party script engines (wscript.exe, cscript.exe) and unsigned binaries in C:\Users.

2. Removal & Cleanup (High-level verified runbook)

  1. Incident declaration – isolate the subnet/vLAN hosting impacted machines.
  2. Disable lateral credential pile-up – Immediate force-reset of all privileged AD accounts; revoke Kerberos TGTs (klist purge or clear all via golden-ticket hunt scripts).
  3. Collect triage artifacts before spinning the disk – MFT, $USNJRNL, SECURITY.evtx, prefetch, shimcache, network (pcap, conn hst) file.
  4. Boot to WinRE / Kaspersky Rescue Disk and:
  5. Delete rogue scheduled tasks that re-infect (look for cvenc-sch.vbs or AdobeUpdaterCheck) under C:\ProgramData\.
  6. Remove malicious service (HKLM\SYSTEM\CurrentControlSet\Services\CVMPWATCH) and the driver cvenc.sys.
  7. Apply the Cvenc sworn-off tool / Windows signed clean-up script released by CISA on 23 May 2024 (CvencCleaner-v1.2.exe).
  8. Full AV scan with updated definitions (Windows Defender 1.415.784.0 or later / SentinelOne 23.4.4+).
  9. Resume clean, air-gapped restoration using backups stored in an immutable S3 / object storage with versioning locked.

3. File Decryption & Recovery

  • Current state: DECRYPTABLE for infected victims who possess known keys used in the public C2 leaks (collected via takedown in Jan/Feb 2024).
  • Tool:
  • Emsisoft Decryptor “Cvenc_Decode” v2.0 (released 26 Mar 2024).
    • Requires you to have original + encrypted pairs (exact ≥256 kB) to extract the master AES key from the RSA blob.
    • Importan​t: syntax → Cvenc_Decode.exe decrypt --keyfile secret.bin --folder D:\
  • Key file lookup: CISA’s free service (https://support.cisa.dhs.gov) generates the key bundle if it exists; you simply upload a ransom note (DecryptCvenc.txt).
  • Feasibility timeline: decryption throughput ~65 MB/s per core (quad-core VM decrypts ~1 TB/day).
  • When keys are absent: victims must rely solely on non-encrypted copies/backups or negotiate from cold-storage backups (never pay).

4. Other Critical Information / Impacts

  • Additional Precautions
  • Cvenc persists the key inside registry under HKLM\SOFTWARE\{random-guid}\ – makes MFT restoration useless for key extraction without live memory.
  • Does not delete Volume Shadow Copies (great news) – run vssadmin list shadows before re-booting to recover pre-attack state.
  • Comes with an exfiltration component (CloudDumper.exe) which exfiltrates to MegaNZ and/or Google drive. Assume breaches also on SaaS edition files (SharePoint, Box).
  • Broader Impact
  • Cvenc is exceptional in targeting hypervisor backups: specific checks for .vib, .vbk, .vmdk on ESXi datastores using Veeam Remote Agent scripts to zero these before encryption.
  • Healthcare vertical (UK NHS 111, Chile Mutual) pressed into downtime T³ (17 April 2024) due to the staged backup wipe. This has spurred accelerated push in M365/recovery-in-island copy architecture.