Allow viewing of CHM files across the network

Microsoft have released a patch to fix a vulnerability in HTML Help (MS05-026 (896358)). This patch disables the ability to view Compressed HTML (CHM) files placed on a remote computer, and one will get the following error message:

this page cannot be displayed

Action cancelled.

Navigation to the webpage was cancelled.

To view the CHM file one have to download the CHM file to the local computer to view it properly. Even if having downloaded the CHM file to the local computer, then one might experience a security warning when opening the CHM file. It is is possible to unblock file and avoid the warning.

If in an environment where the computers (and the users) in the Intranet Zone can be trusted, then one configure the HTML Help viewer to allow viewing of CHM files placed on a local network drive. Create the following registry key:

[HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \HTMLHelp \1.x \ItssRestrictions]
MaxAllowedZone = 1

More Info MS KB892675
More Info MS KB896054



  1. B says:


    Just wanted to say that I've been searching the net for a solution on how to view chm-files from a network share on my Vista-system. None of the registry editing i found worked for me and I don't want to copy them to my local drive. If you have the same problem as me there is one simple solution: use a different chm-viewer. I'm using xchm ( and it is working perfect.

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