Remko Weijnen's Blog (Remko's Blog)

About Virtualization, VDI, SBC, Application Compatibility and anything else I feel like

Archive for December, 2007

Why TSAdmin crashes on Windows Vista

Have you ever tried running the Terminal Server Administration tool (aka TSAdmin) on Windows Vista? You would need it to remotely administer windows 2000/2003 Terminal Servers. If you try to run it you will get an Access Violation but why? I found the answer to this question today because I was testing my TSAdmin replacement on different Windows versions. Just like TSAdmin I use an (undocumented) function from Utildll.dll called ElapsedTimeString. It’s a very simple function that returns a formatted elapsed time string (as seen in the Idle time column from TSAdmin).

While my TSAdminEx ran fine on Windows XP, 2003 and even 2008 it would crash on Vista. Investigation showed that the stack was corrupted in the process of enumerating processes and sessions. Eventually I pinned it down to ElapsedTimeString but could not understand what went wrong. At least not until I investigated Utildll.dll version from Windows Vista. In what was probably an attempt from Microsoft to produce safer code they replaced wsprintfW by StringCchPrintfW. But StringCchPrintfW has an additional parameter (count of characters) so they introduced a new parameter to ElapsedTimeString. Now that’s not a smart decision as this directly breaks compatibility with software that uses this API, but they probably thought that it wasn’t issue since TSAdmin is not included with Vista (I don’t know of any other MS tool that uses this API).

But why doesn’t the Access Violation appear on Server 2008? Is this still using wsprintfW for string formatting? The answer is no, they also use StringCchPrintfW but use a fixed 15 character length. (so they “fixed” the issue).

That leaves you with 2 options if you still want to use TSAdmin on Vista:

  1. Patch TSAdmin or Utildll
  2. Use my TSAdminEx instead which also offers some extra functionality over TSAdmin (I hope to finish it soon, should you wish to beta test then leave a comment).

For now I’ll leave you with a screenshot (click to enlarge) of the current Beta version. As you can see it returns detailed information in the process tab like Memory Usage, Virtual Memory Usage, CPU Time and Process Age.

TSAdminEx Beta Screenshot

Undocumented API’s from Utildll

Several of Microsoft’s Terminal Server tools use undocumented API’s from Utildll.dll. For instance Terminal Server Admin uses it to get a localised connect state string and to format time strings like idle time, logon time etc.

Functions below seems to be the most usefull ones, I will add those to the JwaWinsta unit:

  • function StrConnectState (returns localised string of the given ConnectState)
  • DateTimeString (returns formatted date timestring according to user’s timesettings)
  • function CurrentDateTimeString (like the name says)
  • function ElapsedTimeString (returns formatted string with elapsed time as in TSAdmin)
  • function CalculateElapsedTime (returns elapsed time in seconds)
  • function CalculateDiffTime (returns time difference in seconds)
  • function GetUnknownString (returns localised “unknown” string)

Citrix has it’s own version of this DLL called CUtildll.dll which is similar but uses (Citrix) MUI for localising strings.

IDA 4.9 released as freeware

Datarescue has release IDA 4.9 as freeware. IDA Pro is the de-facto standard for the analysis of hostile code, vulnerability research and reverse engineering in general. You can find IDA freeware here:

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