Ensure 'maxURL request filter' is configured

LowLevel 2Automatediis

Description

The maxURL attribute of the <requestLimits> property is the maximum length (in Bytes) in which a requested URL can be (excluding query string) in order for IIS to accept. Configuring this Request Filter enables administrators to restrict the length of the requests that the server will accept. It is recommended that a limit be put on the length of URL. requestLimits maxUrl must be 4096 or lower at server level and for every site (default 4096). 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/security/requestFiltering/requestLimits' -PSPath $_; [long]$c.maxUrl -gt 4096 }); 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/security/requestFiltering/requestLimits -Name maxUrl -Value 4096

Properties

Operating systems: Any
Tags: iisrequest-filtering
Reference: CIS Microsoft IIS 10 Benchmark v1.2.1 - 4.2 Ensure 'maxURL request filter' is configured

Check this host

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

shell

tmaegis scan --target iis --level 2