Ensure the Zoom client blocks connections with untrusted TLS certificates

MediumLevel 1Automatedzoom

Description

Without this, users can accept an untrusted certificate and expose meeting traffic to interception. Audit reads HKLM:\SOFTWARE\Policies\Zoom\Zoom Meetings\General\BlockUntrustedSSLCert (value or 'unset'); compliant when 1. Confirm the value name against the Zoom Group Policy options article for your client version.

How it is checked

Audit method: Windows registry

registry

$v = (Get-ItemProperty -Path 'HKLM:\SOFTWARE\Policies\Zoom\Zoom Meetings\General' -Name 'BlockUntrustedSSLCert' -ErrorAction SilentlyContinue).'BlockUntrustedSSLCert'; if ($null -eq $v) { 'unset' } else { "$v" }

Expected output: 1

How it is fixed

Fix method: Shell command

shell

$p = 'HKLM:\SOFTWARE\Policies\Zoom\Zoom Meetings\General'; if (-not (Test-Path -Path $p)) { New-Item -Path $p -Force | Out-Null }; Set-ItemProperty -Path $p -Name 'BlockUntrustedSSLCert' -Value 1 -Type DWord

Properties

Operating systems: Any
Tags: zoomtls
Reference: CIS Zoom Benchmark v1.0.0 - Block untrusted SSL certificates

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell

tmaegis scan --target zoom