log4Net eventlog permissions issue using non-administrator account - iis-7

Question

This probably isnt an issue with SiteCore per se but I've included it for completeness. I have sitecore 6.3 running under IIS7 using a custom identity for the app pool. I cant get Sitecore to write its logging information (using the default log4net settings) to the eventlog. I've followed the advice here: http://logging.apache.org/log4net/release/faq.html#Why%20doesn%27t%20the%20EventLogAppender%20work? and although it works fine when I make the custom identity a member of the administrator's group I need to find a way to get it working in production without such a security hack.
The weird thing is that I have a MSI that installs it (running under an account which IS a member of the administrator's group) and creates the correct registry keys in the eventlog for me and yet despite that, I am still getting the following error when I run the application using the custom identity (without it being a member of administrators).
log4net:ERROR DOMConfigurator: Could not create Appender [EventLogAppender] of type [log4net.Appender.EventLogAppender]. Reported error follows.
System.Security.SecurityException: Requested registry access is not allowed.
at Microsoft.Win32.RegistryKey.OpenSubKey(String name, Boolean writable)
at System.Diagnostics.EventLog.GetEventLogRegKey(String machine, Boolean writable)
at System.Diagnostics.EventLog.FindSourceRegistration(String source, String machineName, Boolean readOnly)
at System.Diagnostics.EventLog.DeleteEventSource(String source, String machineName)
at log4net.Appender.EventLogAppender.ActivateOptions()
at log4net.Repository.Hierarchy.DOMHierarchyConfigurator.ParseAppender(XmlElement appenderElement)
The Zone of the assembly that failed was:
MyComputer
log4net:ERROR DOMConfigurator: Appender named [EventLogAppender] not found.
Thinking I could narrow it down to a registry permission issue I granted Everyone full permissions to the following registry key and subkeys but it didnt work either: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\eventlog
The custom identity is a member of the following groups:
Event Log Readers
IIS_USERS
Performance Monitor Users
I've also seen the following question which seems to ask the same thing. The Microsoft article seems to suggest it might be a problem with ACLs on an event log and gives examples on how you can change SSDLs but I'd rather avoid that if at all possible.
EDIT:
I have another server running where the log is being populated fine. The custom identity was a member of administrators so I revoked that and rebooted, trying to purposely break it but I cant. Config is identical on both boxes and same identity used to run the MSI which creates the registry keys. Have run procmon on both (after doing a IISReset and spinning up the app pool again) to examine registry activity. Strange thing is - on the box that works you get 477 name not found records for my event source in the wrong places (Application, and a different Custom EventLog "MyCompany"). No hits for the place where it is logging which is "MyCompany\MyCompany.SiteCore". Whilst on the box which is broken, it does appear to be requesting to read the right key (albeit only 6 times) but you then get the Log4Net registry access error.

Answer 1

As I understand it EventStores are stored in the registry, so you only need write permission to registry to create or delete an EventStore. This is usually only needed once and most applications create this as part of the install procedure so that the application does not need to be run as Administrator during normal execution.
However your error message (in the question) includes the method DeleteEventSource from which I would deduce/guess that the EventSource does exist but is wrong in some way. So perhaps this is currently registered as writing to the event log named MyCompany and you are now trying to change it to "MyCompany\MyCompany.SiteCore" which requires you to delete the old eventsource and create a new one.
So it sounds like your installation routine is creating a different EventSource from the one that your application is actually using.
If that doesn't help, then I would suggest enabling internal logging for Log4net (but obviously not to the eventlog) which will probably give you more information.
Giving full permission to the registry key is not enough.
According to Microsoft
To create an event source in Windows Vista and later or Windows Server 2003, you must have administrative privileges.
The reason for this requirement is that all event logs, including security, must be searched to determine whether the event source is unique. Starting with Windows Vista, users do not have permission to access the security log; therefore, a SecurityException is thrown.
Starting with Windows Vista, User Account Control (UAC) determines the privileges of a user. If you are a member of the Built-in Administrators group, you are assigned two run-time access tokens: a standard user access token and an administrator access token. By default, you are in the standard user role. To execute the code that accesses the security log, you must first elevate your privileges from standard user to administrator. You can do this when you start an application by right-clicking the application icon and indicating that you want to run as an administrator.

Answer 2

I think, contrary to the Apache documentation, log4net DOES need write access to the registry – or at least it does in my case. To prove this, I backed up the registry on the server where it wasnt working and granted IIS administrator privileges before spinning up sitecore. Sure enough it started logging away to the eventlog nicely and then when I exported the registry again to run a diff, there WAS a difference.
The value for the eventlogmessage file on my event source had been updated from:
C:\Windows\Microsoft.NET\Framework\v2.0.50727\EventLogMessages.dll
To
C:\Windows\Microsoft.NET\Framework64\v2.0.50727\EventLogMessages.dll
So I assumed that merely changing this value in the registry by hand would work.
But it didn’t.
So I ran procmon on the two servers I have: A=the working one, B=the failing one. Sure enough, on server B I have a line which says:
Operation: RegOpenKey, Path: HKLM\System\CurrentControlSet\Services\EventLog, Desired Access:Read/Write, Result: ACCESS DENIED.
I’ve traced through with Server A and in exactly the same place, the key is requested with Desired Access:Read.
Conclusion:
It seems unavoidable that I will need to grant my app pool identity administrator privileges in production for at least enough time to programatically do the necessary registry writes the first time from within log4net. I dont know why administrator; I have tried granting Full permissions to the entire eventlog node in the registry for my custom app to no avail. It seems to do something which I cannot identify or pin down. I will then revoke this privilege immediately after it starts to log and monitor whether subsequent installs knock out the functionality afterwards. (Hopefully not).
If anyone has any insight into this behaviour it would be greatly appreciated.