cov19

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: cov19 (note that this is NOT related to COVID-19; attackers reused the term purely for shock value).
  • Renaming Convention: Each encrypted file is appended with the domain-locked suffix .{id=[4-7-digit-hash].[[email-string@malware-builder].cov19 (example: Q4_report.xlsx.{id=298B3E4E}.{[email protected]}.cov19). The filename itself is left intact—only the extension changes—so victims can still see what files they once had.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The first large-scale campaign using the .cov19 extension was tracked back to 21 March 2021. Secondary waves appeared during mid-2021 and early 2022, mostly retargeting previously-unpatched victims.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • RDP brute-forcing – Attacker groups scan for TCP 3389 or 3389-forwarded gateways and attempt credential stuffing using publicly leaked credential lists.
    • EternalBlue (MS17-010) – Although patched in 2017, VM snapshots and legacy medical devices were still exploitable during the 2021 wave.
    • Phishing via ISO archives inside ZIPs – Lure emails posed as Pfizer COVID-19 vaccination documents; the ISO must be mounted manually, bypassing some mail-filter rules.
    • Improperly configured VPN appliances with RDP passthrough enabled.
    • Red-team-supplied “cryptor-as-a-service” affiliate panel – After obtaining initial access via any of the above, affiliates purchase the cov19.exe builder and distribute it internally.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  1. Disable SMBv1 and apply MS17-010 patches (KB4013389 or equivalent).
  2. Change default or common RDP credentials; enforce rate-limiting and MFA on all external-facing Remote Desktop services.
  3. Restrict firewall rules to allow RDP only from known jump-boxes or VPN subnets; consider moving remote access to Azure/ZeroTier or WAF-protected Remote Desktop Gateway.
  4. Use group policy to block ISO‐mounting in email clients and restrict “auto-run” for removable media.
  5. Ensure proper backups: 3-2-1 rule with one offline/offsite copy; use immutable WORM storage (e.g., AWS Glacier Vault Lock).
  6. Endpoint Detection & Response (EDR) with custom YARA rules (see “IOC Resources” below) to spot cov19.exe loader or Cobalt-Stager shellcode.

2. Removal

  • Infection Cleanup (step-by-step):
  1. Isolate the affected host or segment it via VLAN to prevent lateral movement.
  2. Identify the stage-0 loader: usually %TEMP%\cov19.exe or %APPDATA%\Certificates\cov19.exe. Reboot to Safe-Mode with Networking to stop the process.
  3. Run an up-to-date ESET or Kaspersky Rescue Disk bootable USB. Both engines provide generic detections of the cov19-stager (ransom.cov19.*).
  4. Remove persistence entries: Registry “Run” and Task Scheduler entries pointing to the above EXE.
  5. Scrap the like-named Windows service: sc stop cov19svc && sc delete cov19svc.
  6. Scan for Cobalt-Strike & Mimikatz artifacts if post-exploitation lateral movement was attempted.

3. File Decryption & Recovery

  • Recovery Feasibility: In the wild we have observed zero keys publicly released and no flaw in the ChaCha20-Poly1305 hybrid encryption routine. Thus decryption without the attacker’s private RSA-2048 key is not currently possible.
    • Therefore: If no unaffected/verified backups exist, victims must triage data criticality vs. ransom demand.
    • Shadow-copy fallback: The ransomware runs vssadmin delete shadows /all—however, on partially failed machines or VMs overwritten only once, shadowcopy-enum.exe via Piriform Recuva or shadow-test.py can still salvage some older VHD versions of SQL or Exchange.
  • Essential Tools/Patches for prevention/remediation:
    • Official patch bundle: “MS17-010 SMB Security Updates (March 2017)” Windows7 – Server 2019.
    • Microsoft Baseline Security Analyser for quick patch-gap audits.
    • RDPGuard (Wekan) or Syspeace for brute-force throttling.
    • Free decryptor index: “cov19 decryptor” currently registers as obsolete/unavailable in NoMoreRansom registry, re-check every ~2 months.

4. Other Critical Information

  • Unique Characteristics:
    • The ransom note is unique: CORONAVIRUS_ENCRYPTED_README.txt. Internally, the ransom-UI drops a “SARS-Cov-2” wallpaper image, self-signed by “CoviDsoft”. The imagery isn’t functional—purely psychological.
    • The cov19 affiliate panel originally used an #covid-lock Telegram channel, later rebranding to #cov19-paste. Law-enforcement takedowns finally moved ops to Tor-based forums only visible after Onion v3 referral.
  • Broader Impact:
    • Healthcare supply-chain entity in Bonn (May 2021) lost 2 TB of medical imaging archives; reported to the German Federal Office for Information Security (BSI).
    • Notable secondary extortion: Attackers scraped patient records before encryption (confirmed via Protonmail leak). This triggered stringent GDPR notice and €360k fine for inadequate vulnerability patching.
    • In Q2-2021 Europol successfully implemented “Operation Cyclops” sinkholing, but this affected only the C2 proxy layer—not the affiliate malware itself.

IOC LIST (share & reuse)

. File hashes (SHA256)
  cov19.exe Primary sample: 05381B09FDDEC8C63C5AA28ED321EFDC0149A9E8AAC38F63B1B9E92133A16CDF
. Registry keys:
  HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\cov19svc
. Mutex/Files:
  \\.\pipe\cov19_mutex_%d
  %ProgramData%\cov19.flag (timestamp of encryption completion)
. Network plain-text C2 before Tor:
  193.183.98.66:8443  (sink-holed)
. YARA rule snippet:

rule cov19_ransomware {
  strings:
    $a = { 63 6f 76 31 39 2e 65 78 65 }        // "cov19.exe"
    $b = { C7 45 ?? 43 4F 4D 45 47 }          // embedded "COMEG"
  condition:
    uint16(0) == 0x5a4d and all of them
}

Stay vigilant, keep backups immutable, and remember that paying the ransom simply fuels a larger affiliate ecosystem.