Vulnerability in EPiServer.Forms

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Johan Björnfot
Nov 15, 2016
(8 votes)

Internationalized Resource Identifiers (IRIs)

An Internationalized Resource Identifier (IRI) is a network address that contain non ASCII characters as below:

Image IRI.png

EPiServer CMS has previously (prior to 10) only allowed characters in url segments according to RFC 1738 which basically allows ALPHA / DIGIT / '-'/ '_'/ '~' / '.'/ '$'/. 

It is now (from CMS.Core version 10.1.0) however possible to define a custom character set that are used for url segments and simple address. This is done by registering an instance of UrlSegmentOptions with a custom regular expression in IOC container. When an expression is set that allows characters outside RFC 1738 the setting UrlSegementOptions.Encode is recommended to be set to true so that url:s gets properly encoded. Below is an example of how a character set that allows unicode characters in the letter category.

using EPiServer.ServiceLocation;
using EPiServer.Framework.Initialization;
using EPiServer.Framework;
using EPiServer.Web;

namespace EPiServerSite6
    public class IRIConfigurationModule : IConfigurableModule
        public void ConfigureContainer(ServiceConfigurationContext context)
            context.Services.AddSingleton<UrlSegmentOptions>(s => new UrlSegmentOptions
                Encode = true,
                ValidUrlCharacters = @"\p{L}0-9\-_~\.\$"

        public void Initialize(InitializationEngine context)

        public void Uninitialize(InitializationEngine context)

UrlSegmentOptions also exposes a CharacterMap property where it is possible to define a mapping for unsupported characters, for example 'ö' => 'o'. 

Internationalized Domain Names (IDN)

As explained in IDN and IRI are internationalized domain names registered in its punycode format (a way of representing Unicode characters using only ASCII characters). 

Internationalized domain names should be registered in admin mode under Manage Websites in their punycode format. 

Nov 15, 2016


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