Starting to build your own Credential Provider

If you’re starting to work on a Credential Provider (CredProv or CP, for short) for Windows Vista, Windows Server 2008, Windows Server 2008 R2 or Windows 7, there are a few steps I would strongly recommend you take, because it will make life easier for you.

0. Read Dan Griffin’s article in MSDN Magazine.

The article, "Create Custom Login Experiences With Credential Providers For Windows Vista" by Dan Griffin in January 2007’s MSDN Magazine on Credential Providers is a truly excellent source of information, gleaned largely by the same exhaustive trial and error effort that you will be engaging in with your own CP.

0.1 Read it again.

0.2 And again, and again and again.

As you work on your CP, you will keep running into questions and new insights as to what it is that Dan was telling you in that article.

Keep a printed copy next to you when developing your CP, so that you can keep looking back to it.

If you have met Dan and asked his permission, keep him on speed-dial.

1. Test your Credential Provider in a Virtual PC environment.

You will screw something up, and when you do, the logon screen will most likely cycle over and over and over (what, Microsoft couldn’t provide a “this Credential Provider has failed eighteen times in a row and will be temporarily disabled” feature?), preventing you from logging back on to change out your broken CP. At this point, you really want to revert back to a previous working session.

To my mind, the easiest way to do this is to create one Virtual PC environment with a base Windows 7 system, patched up to current levels, and with a few test users installed. You can burn an MSDN licence up on this test installation, if you like, but quite frankly, I’m likely to want to refresh it from scratch every so often anyway, so the activation timeout is no big deal.

Once you have created this base image, create another virtual machine, based off the virtual hard disk (VHD) of the base image, and be sure to enable undo disks. This way, when things go wrong, you can shut down this second virtual machine, telling Virtual PC to discard the Undo Disk data, and you will be able to restart the machine immediately and continue to work on it.

2. Enable the kernel debugger against your VM.

This is a little tricky.

2.1 First, edit the settings on your VM.

Enable COM1 to point to a Named Pipe, such as “\\.\pipe\credprov”:


2.2 Now, enable kernel debugging on the VM itself

Log on to the VM, and use the bcdedit tool, from an Administrator Command Prompt to change the debugging option in the boot database. You can go the long way around, reading Microsoft’s instructions on how to do this, or you can simply use the following two commands:

bcdedit /dbgsettings serial debugport:1

bcdedit /debug {current} on


Notice that Microsoft suggests creating a separate environment for debugging on and off, but I don’t see that as being terribly useful. I will always be debugging this test environment, and it really doesn’t slow me down that much. You can always use “bcdedit /debug {current} off” to turn debugging off later.

This setting will take effect at the next reboot of the VM, but don’t reboot yet.

2.3 Enable the Debug Output Filter so OutputDebugString works.

Windows Vista and later don’t output debug messages to the kernel debugger by default. Those messages are filtered. You can spend a lot of time trying to figure out why you are staring at a blank screen when you have filled your code with OutputDebugString and/or TRACE calls. Or you can change the registry entry that controls the Output Debug Filter:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Debug Print Filter\DEFAULT

Create the “Debug Print Filter” value, if it isn’t there, and then create the DEFAULT value as a DWORD, and set it to the value 8.


2.4 Save these settings

Since you’ll want these settings to come back after a restart, you’ll want to commit them to the VHD. Easily done, but takes some time. Shut down the VM, and when you are prompted what you want to do, select that you wish to commit changes to the virtual hard disk.


Expect this to take several long minutes. While you do that, go read Dan’s article again.

2.5 Create a shortcut to the debugger

I use WinDBG (is that pronounced “Windbag”?), and the shortcut I use points to:

"C:\Program Files\Debugging Tools for Windows (x64)\windbg.exe" -k com:port=\\.\pipe\credprov,baud=115200,pipe,reconnect,resets=10

Remember to start the VM before starting the WinDBG shortcut, so that the VM has a pipe for WinDbg to connect to.

3. Start from the CredProv samples

Play around with the credential provider sample, or samples, that are closest to your eventual design goal, and add features to move them towards your desired end-state, rather than building your own from scratch.

Don’t just play with the one sample – looking at, or testing, the other samples may give you a little more insight that you didn’t get from the sample you’re working with.

3.1 Build often, and test frequently

Random errors and occasional misunderstandings (“gee, I didn’t realise you can’t call SetFieldString from GetStringValue”) will cause you to crash often. A crash in your CP means an infinite loop, and some inventive use of Anglo-Saxon.

Building often, testing frequently, and backing out disastrous changes (use version control if you have it!) will lead to a better process.

3.2 Later, build your own CP

Once you have a good understanding of the Credential Provider and its mysterious ways, you may decide to throw out Microsoft’s code and build your own from scratch. Keep comparing against your modified sample to see why it isn’t working.

3.3 Before deployment, change the GUID!

The GUIDs used by the sample code are well-known, and will tie in some systems to other, more shoddy, developers’ versions of those samples. If you forget to change the GUID on your code, you will have a CP-fight.

4. Go back to Dan’s article every time you reach a bottleneck

Occasionally a twist of phrase, or a reinterpretation of a paragraph is all it takes to wring some more useful knowledge out of this article. Don’t forget to use the online help Microsoft provides, as well as searching the MSDN, but remember that this is not a very frequently-trod path. It may be that you are doing something the credential provider architects didn’t consider. In fact, it’s highly likely.

5. Stop mailing

Nobody monitors that email address any more, and there seems to be something of a black hole associated with questions related to Credential Providers in general. It’s as if nobody really truly understands them. A few of the MVPs (particularly Dan Griffin, Dana Epp, and perhaps myself) have a good understanding, so read their blogs, and perhaps post to the Microsoft Forums, if you can manage to do so.

6. Enumerate, and test, the scenarios your customers might run into

  • domain-joined and non-domain
  • administrator, non-administrator, guest
  • with and without user names being supplied (Secpol.msc –> Local Policies –> Security Options –> Interactive Logon: Do not display last user name)
  • default domain, other domain, local accounts
  • logon, switch user, unlock workstation, access from Remote Desktop Connection / MSTSC (as we old-timers call it)
  • change password
  • If you’re of a mind, test the credential user interface mode, too.

Things I don’t want to hear in a security interview…

This is probably part 1 of an ongoing series, highlighting some of the key phrases I hear when talking to candidates for security positions. Many of them are also “accepted truths” out on the Internet, and so it’s an opportunity for me to prevent some memes from distributing.

There’s no security advantage between TCP and UDP

Because, clearly, there is. UDP, like ICMP, IP, etc, is frequently forged in order to trigger echo attacks and the like. TCP, by comparison, uses randomised Initial Sequence Numbers (ISN), and while this isn’t enough to allow you to use IP addresses on TCP connections as an authentication mechanism, it’s better than the nothing that you get with UDP.

Closer to the truth: The security advantage TCP has over UDP is minor.

OS <name> is more secure than OS <name>

Each OS is most secure when it is administered by a competent and knowledgeable technician. Me administering a Linux system would be less secure than me administering a Windows system. One of my more Linux-based colleagues, on the other hand, will find that their Linux system is more secure than their Windows system.

Frankly, you don’t buy an operating system for its security, you buy it because it runs the apps you want to buy or want to develop.

Closer to the truth: Some operating systems make it easier to protect against some classes of threats than others.

The firewall protects it

The correct name for the device commonly known as a “firewall” is a “hole wall”. OK, so I’m joshing a little there, but while a firewall will prevent many errant connections, that’s only going to help if you don’t have open ports for vulnerable services – and you wouldn’t be putting the system on the network if it didn’t need to be reachable at some point, through a hole (or holes) punched in the firewall.

Web application firewalls (WAFs), IDS, IPS etc have similar purposes – keeping out the bad stuff, and letting in the good stuff, but then you have to spend a lot of time defining what’s good and what’s bad. Then you have to hope that the “good” you let in doesn’t also encompass some “bad” to which you are vulnerable.

Again, firewalls provide value, but they’re not the complete protection many assume.

Closer to the truth: The firewall protects the device from having to handle and reject traffic the device does not intend to receive. This leaves the device freer to protect itself from traffic on its intended port.

I studied this on YouTube / Google / FaceBook / the web

YouTube is the home of many a poor video on security topics, including the (unintentionally) hilarious NextGenHacker101 teaching us how to use “tracert” to count the users on Google. Similarly, while there are many good sources of information on the web, there’s also a lot of really bad information, and some of it is not so obviously bad as my YouTube example.

Even this blog, a paragon of fine security advice, occasionally treads into the sarcastic and ironic, or just plain aims to deliver pithy ‘sound-bite’ length advice, which may not completely satisfy the subtleties of imparting good knowledge.

You can’t beat a good book, technical article, training class, or other ‘official’ source, when it is combined by experience, experimentation and exasperation. The three Xs, if you will.

Closer to the truth: I use Twitter / Bing / Blogs to catch up on what my favourite security researchers are doing today, and then I go and research what I read elsewhere to make sure that I’m not responding to tat.

I learned everything I needed to know in my <name> certification study class

No you didn’t, you learned how to pass the certification. At least, that’s what I’ve learned from certification classes – including some extremely sketchy security information and downright outdated and historical technologies that I would be embarrassed to suggest using in a real life environment.

I won’t say it wasn’t useful studying some of that material – I certainly learned a few new tricks from cert classes, although I also learned that a great many people have certifications that are not indicative of anything more than their desire to spend several hours dumping information into their heads, and another hour or two dumping it back out. Much like pouring milk into a jug and then out again, there are some vessels that remain surprisingly clean after the fact.

Closer to the truth: I train to improve my knowledge without having to slowly gain experience through my own mistakes. I get certified because it impresses some people (HR, other teams, etc), and sometimes that’s a necessary first step..

Security is all about being paranoid

No it’s not – security is about knowing and accepting, transferring or mitigating the risks to those assets you and your business deem to be valuable. That will include monetary equivalents (such as credit cards or gift cards), reliability / availability, privacy, and such intangible items as trust. Being overly paranoid prevents many businesses from actually achieving some of their business goals, and can cost more than it saves.

Closer to the truth: The ability to act paranoid can help greatly when enumerating threats. But not every threat is realisable, and not every threat can be protected against at a reasonable cost. A paranoid mindset will not see or accept that.

You have to think like an attacker

Not really – though this is something worth telling developers who haven’t thought about security, if only to make them think of a new paradigm. But then you have to move them through this mode. [Many developers still do not understand that their application may be the target of an attack]

What you have to do is think like a defender, because attacker and defender have very different goals.

While an attacker is looking for a single instance of a flaw or vulnerability, a defender’s time is best spent looking for, and addressing, whole classes of vulnerabilities at a time.

A QA / Tester might find benefit in thinking like an attacker, but they are usually already pretty comfortable with the idea of trying to anticipate what the developers didn’t think of.

Closer to the truth: There are people out there, thinking like an attacker, and ready to attack your code. You have to figure out how to defend against that.

Weird virus / anti-virus behaviour

My wife and I pent a while this weekend trying to figure out how to rescue a Media Center that seemed to be going a little loopy.

The Windows Media Center application itself worked fine, as did Windows Media Player, Calc, etc.

Only Internet Explorer was failing.


If you press Ctrl-C from most Windows dialog boxes like the one above, it will copy the text of the dialog into the clipboard.

Here’s what I get if I do that (this is mostly aimed at people using search engines):

[Window Title]
C:\Program Files (x86)\Internet Explorer\iexplore.exe

C:\Program Files (x86)\Internet Explorer\iexplore.exe

The parameter is incorrect.


[Had the Media Center been on 32-bit Windows, those paths would simply be “C:\Program Files\Internet Explorer\iexplore.exe” – the error message would still be “The parameter is incorrect”]

So, what on earth does this mean?

It seems bizarre, partly because there isn’t a parameter I’m supplying to Internet Explorer, but mostly because it gives me chills whenever Internet Explorer dies so quickly – I’ve seen so many viruses that disable Internet Explorer (so you can’t download a fix), that an IE issue like this sends a shiver down my spine.

My wife had the first go at fixing this, trying not only removing and re-adding IE as a Windows Feature (in “Turn Windows Features On or Off”), but also reinstalling Windows 7 on top of itself, as a repair. No fix.

Meanwhile, I downloaded Mozilla Firefox and Google Chrome on a different computer, moved them over to this one, and installed them each.

Both of them, when I tried to run, came up with the same “The parameter is incorrect” message. Worrisome.

I fire up Regedit, which is almost always also disabled by viruses that want you not to fix them. Strangely enough, that works – but I’m not done with my virus theory.

I updated Microsoft’s Security Essentials – which is already running on this system. A Quick Scan finds nothing. Trend Micro’s HouseCall is another “download and run this” virus scanner, much like the Microsoft Malicious Software Removal Tool, which arrives monthly with your Windows Updates.

Still nothing detected.

I get by with a little help from my friends

Fortunately, my friend and fellow MVP, Susan Bradley, is online, and although I don’t think she has the bandwidth to answer everyone’s questions, I think I’m rather special, so I call on her time to see if she has any suggestions.

“try” she asks.

Sure enough, I hadn’t, and I know that several of the Consumer Security MVPs swear by it. So I download it and run it.

It finds four infections (I never get excited about the number of infections these tools find, because some of them are really aggressive as to what they think are “infections” – I’m one of those strange people that thinks tracking cookies are “mostly harmless”).

Reviewing what they are, I can see exactly how the behaviour comes about, but I’m still at a little of a loss as to how that happened.

The four entries it finds are under Registry settings, in the registry tree HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options, and under keys called “iexplore.exe”, “chrome.exe”, “firefox.exe” and “opera.exe” (Opera is another browser you can download).

The value, in each case, is as follows (using RegEdit to see):


The value name is “Debugger”, and although you can’t see it clearly there, the value is “ -sb” – that is a single space, followed, by a hyphen, and the two letters “sb”.

This is a variation on a classic method for killing Internet Explorer – or rather, for sidelining it, or prepending it with your own code. The functionality has a good purpose – for developers who want to run their debugger every time they open an application. I use it a lot myself.

I haven’t seen anyone do exactly this, though – it seems like they screwed up somehow.

The Fix

Fixing this is really simple. You just have to remove the value named “Debugger” from that key. Watch that you don’t make other changes, in case those cause other behaviours you don’t want. Oh, and do this as an administrator, or you won’t actually make any changes.

In my case, since this was the only value in the key for Internet Explorer, Firefox, Chrome and Opera, I deleted the keys themselves, just to be safe.

No reboot required – suddenly, I can start up my browsers – all of them. Thank you, Susan, and thank you, MalwareBytes!

The cause?

I’m always keen to find the cause of issues like this – especially since this could still be a virus that caused this, and if it is, I think the Microsoft Security Essentials team would like to know about it.

Searching leads repeatedly to the same possible target – a ROGUE antivirus program, which calls itself “AVG Antivirus 2011”, but which actually has nothing to do with the real AVG Antivirus. I’ve heard of this before, and I’ve seen it at a couple of sites I’ve visited for “research purposes”, but each time I’ve simply closed down IE before it had a chance to run its alleged scan.

[Hint: no web site should be scanning your computer and finding viruses. If a web site says it’s found a virus, it’s referring to the one it’s about to install on your system.]

So, it could have been me, it could have been a family member – but no real harm done. My guess is that it started to install itself, and Microsoft Security Essentials started to remove it, but didn’t quite manage to complete the job. That’s just a guess. I don’t have nearly the resources or the interest to try and re-stage the incident to test! I’m putting this blog entry out in the hope that it’ll be a search engine hit when someone else runs into the same issues.

No more IPv4 /8s – Oodles of IPv6 /64s and /48s.

[Additional note: Bing and Juniper Networks just announced that they will also be joining in World IPv6 Day.]

IANA just held a ceremony (streamed live, and with a press conference following at 10amEST) to hand out the last of the IPv4 /8 blocks to Regional Internet Registries – RIRs.


It’s a quiet, but historical moment, as it truly marks the time we can finally tell people “yes, I know nothing appeared to be happening, but finally it’s happened”. Preparing for IPv6 has to happen, because there just isn’t any stopping this particular juggernaut. IPv4 addresses will run out, and there will arise a time when web sites can no longer find a public IPv4 address.

BEFORE that happens, something has to change to allow us to work together on an IPv6 Internet. I’m doing what I can.

As a client user, I live on the Hurricane Electric IPv6 Tunnel Broker, because Comcast have yet to extend their IPv6 trial to my neck of the woods, seeing as how I live in technology-deprived Seattle.

I’m still trying to persuade my web site’s ISP, 1&1, to put an IPv6 capability in place before World IPv6 Day on June 8, so I can host my web page there in IPv6, but I definitely have my FTP server software, WFTPD and WFTPD Pro, ready to support IPv6 fully.

What are you doing?