Ensure IIS HTTP detailed errors are hidden from displaying remotely

MediumLevel 1Automatediis

Description

A Web site's error pages are often set to show detailed error information for troubleshooting purposes during testing or initial deployment. To prevent unauthorized users from viewing this privileged information, detailed error pages must not be seen by remote users. This setting can be modified in the errorMode attribute setting for a Web site's error pages. httpErrors errorMode must be DetailedLocalOnly or Custom at server level and for every site. PowerShell 5.1 with the WebAdministration module; run elevated.

How it is checked

Audit method: Shell command

shell

Import-Module WebAdministration -ErrorAction Stop; $paths = @('MACHINE/WEBROOT/APPHOST') + @(Get-Website | ForEach-Object { "IIS:\Sites\$($_.Name)" }); $bad = @($paths | Where-Object { $c = Get-WebConfiguration -Filter 'system.webServer/httpErrors' -PSPath $_; [string]$c.errorMode -notin @('DetailedLocalOnly', 'Custom') }); if ($bad.Count -eq 0) { 'compliant' } else { 'noncompliant' }

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Set-WebConfigurationProperty -PSPath 'MACHINE/WEBROOT/APPHOST' -Filter system.webServer/httpErrors -Name errorMode -Value DetailedLocalOnly

Properties

Operating systems: Any
Tags: iisinformation-disclosure
Reference: CIS Microsoft IIS 10 Benchmark v1.2.1 - 3.4 Ensure IIS HTTP detailed errors are hidden from displaying remotely

Check this host

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

shell

tmaegis scan --target iis