IE Content Advisor & NT registry permissions allow 'per user' browsing restrictions

One user thinks he found an unknown bug in IE. He's made some interesting conclusions based duping it in a test environment.

I ran into this problem whilst trying to lock down Web access on a Metaframe server farm at a high school. It seemed...

that when we added sites to the restricted list in IE's Content Advisor, the administrator could not access them, however other users could still browse to the sites!

It appears that we hit a bug in IE that, to my knowledge, is as yet unknown at MS. I certainly could not find any references to it on Microsoft's knowledge bases. I did find several other reports, on technical forum sites, from administrators experiencing the same problem -- but no solutions.

I was able to reproduce the problem in a test environment, and have come to the following conclusions:

  1. This function is definitely set on a per machine basis. No information is written to the users' hive of the registry when changes are made to the accepted sites list.

  2. The site list information is stored in the registry in the following location:

    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionPoliciesRatingsPICSRules.Default0PRPolicy
    "PRNumPolicy"=dword:00000001
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionPoliciesRatingsPICSRules.Default0PRPolicy0
    "PRPPolicyAttribute"=dword:00000001
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionPoliciesRatingsPICSRules.Default0PRPolicy0PRPPolicySub
    "PRNumURLExpressions"=dword:00000001
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionPoliciesRatingsPICSRules.Default0PRPolicy0PRPPolicySub0
    "PRBUInternetPattern"=dword:00000001
    "PRBUNonWild"=dword:0000000c
    "PRBUSpecified"=dword:0000001f
    "PRBUHost"="www.yahoo.com"
    "PRBUPort"="80"
    "PRBUUrl"="www.yahoo.com"

  3. Additional sites are added to this structure by copying this, but adding 1 to the numbers above. (e.g. "PRNumPolicy"=dword:0000002...etc.)

  4. Only users with admin rights can change the values in this content advisor section.

  5. Once set on a machine, the site listing should take effect for ALL USERS. This is not the case. The setting does take effect for all members of the ADMINISTRATORS group.

  6. If set by a user without admin rights, the site list will last for an individual session and will block the selected sites, but will not be saved.

  7. In analyzing the permissions on the PICSRules key, we found that, by default, the following permissions are set: ADMINISTRATORS FULL CONTROL, EVERYONE READ.

  8. In order for the settings in the Accepted Sites list to take effect for a user, they require 'Full Control' over the Policies registry key. (Note: It may in fact be possible to limit this a little further to 'change' permissions on the PRPolicy key. However, I have not tested this, as it is largely academic.)

Conclusion: Contrary to instructions listed in the relevant MS technical articles, it appears that on an NT based machine, users require the ability to change these keys in order for the site list to be read into Internet Explorer. Note that this allows us to utilize the 'Allowed Sites' feature in a fashion that is not recognized by MS -- on a 'per-user' basis. I haven't checked this on a Windows 2000 box, but would be interested to hear any results.


This was first published in August 2001

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