WMF Vulnerability is an Intentional Backdoor?

An anonymous reader writes "Steve Gibson alleges that the WMF vulnerability in Windows was neither a bug, nor a feature designed without security in mind, but was actually an intentionally placed backdoor. In a more detailed explanation, Gibson explains that the way SetAbortProc works in metafiles does not bear even the slightest resemblance to the way it works when used by a program while printing. Based on the information presented, it really does look like an intentional backdoor." There's a transcript available of the 'Security Now!' podcast where Gibson discusses this.

I would not be suprised at all.

[AltGrendel (175092)]

I could see someone deliberatly doing this, maybe a contractor or a disgruntled employee.

Its happened before and it will happen again. Whether this is the case remains to be seen.

Re:I would not be suprised at all.

[NtroP (649992)]

I could see someone deliberatly doing this, maybe a contractor or a disgruntled employee.

The problem with that argument is that in order to exploit this backdoor you'd have to get the target computer to load a WMF file. The main practical way to do this would be to embed it in a web page and have the target visit that page. The only sites that all windows machines access on a regular basis are Microsoft's. The employee would also have to have access to Microsoft's web site to exploit this reliably.

This seems to be only useful if MS itself wanted to use it. Use your imagination as to what they'd do with it. I can think of all kinds of things.

Re:I would not be suprised at all.

[QuietLagoon (813062)]

The only sites that all windows machines access on a regular basis are Microsoft's.

I presume you are willing to show the details of your extensive research that determined this factoid....

Re:I would not be suprised at all.

[mrseigen (518390)]

I'm not quite sure why they'd want to use it. End-users already trust Microsoft implicitly because they made the operating system, so if they wanted to, for instance, install some software on all Windows machines that reports home if it detects a pirated copy, they could just do it through a service pack update. Most people would willingly install it (or click the little automatic button in Windows Update), and there'd be none of this Tom Clancy technothriller intrigue.

I can't personally think of any kind of official reason why Microsoft would want to shove code onto Windows machines just from visiting their website. They've got tons of other ways of doing this.

Re:I would not be suprised at all.

[jez9999 (618189)]

Furthermore, if Gibson is so sure of himself, why isn't his own test utility available to everyone?

Eh? I just downloaded it, it's linked to from here [grc.com].

Re:I would not be suprised at all.

[dc29A (636871)]

I could see someone deliberatly doing this, maybe a contractor or a disgruntled employee.
- How about a totally stupid idea that MS thought was good?

I mean MS has a long history of ignoring security for usability, lock in and whatnot. WMF dates back to close to 10 years, back when MS really didn't give a damn about security. Even after a the big Gates propaganda email and Trusted Computing Initiative and all the hoopla, XP SP2 allows blank passwords for administrators, the user created during installation is an administrator, again if password is blank no one gives a shit. Remote registry is on by default. RPC on by default. Administrative shares are on by default. Not to mention a plethora of completely useless services.

MS just doesn't understand security. This WMF example is nothing different. It's some ancient code that never got looked at. Add to that the fact everyone and his mother is root, AND that the OS is a big bowl of spaghetti (hi2u IE deep in kernel), you get another attack vector vs Windows systems.

Did someone maliciously implement this WMF "feature"? I doubt it. It looks like another regular MS security hole that shows that MS has no clue about security.

NSA

[by Anonymous Coward]

Well, how else is the NSA going to fight terrorism?

Government backdoor?

[Jerry_Duplicate (126840)]

There was talk about the NSA/CIA having a close relationship with Microsoft and being able to exploit backdoors in Windows. This could have all been conspiracy theories, but the fact that this vulnerability existed throughout the Windows line kinda seems odd..

If this isn't a glaring example on why you should support open source, I don't know what is....

Re:Government backdoor?

[Dystopian Rebel (714995)]

but the fact that this vulnerability existed throughout the Windows line kinda seems odd.

The function in question has existed for a long time. The exploit is in Windows 2000 and more recent. From the transcript:

But the only conclusion I can draw is that there has been code from at least Windows 2000 on, and in all current versions, and even, you know, future versions, until it was discovered, which was deliberately put in there by some group, we don't know at what level or how large in Microsoft, that gave them the ability that they who knew how to get their Windows systems to silently and secretly run code contained in an image, those people would be able to do that on remotely located Windows machines...

Re:Government backdoor?

[man_of_mr_e (217855)]

Actually, Bruce Schneier's analysis is somewhat different.

http://www.schneier.com/crypto-gram-9909.html#NSAK eyinMicrosoftCryptoAPI [schneier.com]

The fact is, the majority of the people making claims about this don't even understand what it does. The majority of the speculation isn't possible. It doesn't give anyone (Not even Microsoft, much less the NSA) a backdoor into your computer.

Re:Government backdoor?

[einhverfr (238914)]

First you have to understand what the ramifications of this are likely to be.

The NSA is (in theory at least) legally forbidden to spy on Americans. Their main mission involves cryptoanalysis (codebreaking) and signal intelligence. So they spend a lot of time in foreign countries evesdropping on cell phone calls and the like. They have also been very much involved in the development of computerized cryptography (witness their role in the creation of DES). In this latter case, they have probably attempted to balance their interests in codebreaking with the legitimate interests in algorythmically secure encryption (i.e. make DES algorythmically secure, but shorten the key so we can break it if we really have to).

The rise of independant professional cryptography organizations, like RSA, Inc. has created a very serious problem for the NSA in this regard. In general, most of these new systems use variable length keys and are highly peer reviewed for attack potential. So the NSA cannot count on being able to brute force decrypt a document within a reasonable timeframe in the event of a clear and present need to decrypt the information.

Therefore, I believe that most of these are there to allow the NSA to bypass the encryption algorythms in Windows and allow them to access the information without having to attack the encryption. This would make reasonable sense given the NSA history.

Now, I see *no* reason to suppose that the NSA has anything to do with the WMF exploit. Instead, I suggest that this is likely to be a backdoor either put in place by a developer, at the request of a partner (such as the RIAA), etc. This backdoor has *nothing* to do with anything the NSA typically gets involved in, so I think even the most paranoid analysis can rule them out. Instead, this is just a strange attempt to allow the Media Player to be subverted and used in what ever way an attacker decides.

Now, Microsoft's response to this has been inadequate (they only grudgingly developed a patch), which suggests that this backdoor had the blessing of the company, much like the response to the Sony DRM rootkit which was undetected by agreement with First4Internet. Lest I appear to be too hard on Microsoft, I found Symantec's response ("Oh, we will start removing it" when First4Internet claims they were working with Symantec to ensure that it would not be removed) to be far less trustworthy.

Anyway, there is enough doubt in my mind about Microsoft's goodwill on these areas that I would not suggest running Windows in any environment that absolutely requires security. The system has fundamental design flaws from a security point of view, and these problems continue to underscore either serious development issues at Microsoft or an attitude that the security of the customer is not really that important.

Length==1

[atfrase (879806)]

This does look awfully like a special-case trigger. The idea of a backdoor is to have it look for a specifically crafted but completely nonsensical and invalid input sequence -- this serves as the "key" to the backdoor, ensuring that no other designer or user accidentally stumbles onto it. Since we assume that legitimate users and developers will only provide valid input, we design our "key" to be definitely invalid. For me, that length==1 trigger is the most convincing evidence. It's not just that it's the wrong input, it's that it's the one specific value of wrong input that triggers the behavior. That seems like design.

Re:Length==1

[stevied (169)]

Obviously SetAbortProc should not be implemented for WMF playback, but assuming somebody screwed up and just called the normal version of Escape(), could the behaviour we're seeing here not somehow be the result of not checking the validity of the length parameter properly, performing some arithmetic on it, and possibly falling through to some other code that happens to a jump or call?

But wait, there's more...

[IPFreely (47576)]

It that is all it was, then the the same thread would jump into the user code. But wait...

I found was that, when I deliberately lied about the size of this record and set the size to one and no other value, and I gave this particular byte sequence that makes no sense for a metafile, then Windows created a thread and jumped into my code, began executing my code.

So, it accidently created a new thread, and directed the new thread to start executing code at the specific position? That's a whole different level of accident.

Oh, and Shimmer, I'll take that 5$.

Re:Length==1

[Procyon101 (61366)]

Possibly, but I doubt it's a Microsoft sanctioned backdoor. Any "OFFICIAL" backdoor from MS would have a much more complex key to get in than "1".

I can see this being a programmer supplied backdoor, like a hook for easter eggs, but based on the other security work done in MS, anything that can be gotten into that is there on purpose is locked up pretty tight to any casual attempts.

Re:Length==1

[atfrase (879806)]

Agreed, it doesn't seem like the kind of "feature" that was designed in top-secret MS design documents or developed in meetings.

But I still have a hard time seeing how code would *accidentally* behave like this. An invalid length should abort processing right off the bad, for one thing; "falling through" might be an explanation, but what possible code could be "fallen through" into that would set CPU execution *inside* the metafile -- moreover, would set CPU execution to the *next byte* after the erroneous header block. That's awfully convenient; if it were a mistake, I'd expect code execution to begin at some other random location, probably influenced by whatever happened to be in the register or some temporary pointer variable at the time. But the very next byte? That's too insanely convenient -- you get to provide your key *and* your payload in the *same* place.

You could argue that buffer overrun exploits do the same thing, but the idea of the buffer overflow is to specifically overwrite the function-return pointer to *make* it point at your code. In this case, the exploit doesn't have to specify the location of the code to execute, Windows does that for you. Too convenient.

Thread Creation

[Lagged2Death (31596)]

For me, that length==1 trigger is the most convincing evidence.

I don't think it's surprising that a piece of code might behave in an odd way if it's given invalid input, i.e., if a buffer length is wrong.

I think the real giveaway here is that Windows creates a new thread when presented with this magic length. That's like rolling out the red carpet for the attacking Huns. I don't think the average buffer overflow type exploit gets it's own thread or process.

And of course it's still possible that it was all a mistake. The C language can be used to write some extremely tangled code, if one is so inclined. Something like an incorrectly used setjmp/longjmp could have effects like this.

Re:Thread Creation

[atfrase (879806)]

I don't think it's surprising that a piece of code might behave in an odd way if it's given invalid input, i.e., if a buffer length is wrong.

Again, agreed. But again, the catch is in the particular kind of odd behavior. If I were writing that code and it hit an invalid length, I'd probably abort processing of the whole file, presuming data corruption. Failing that I'd just skip over the flawed block and proceed with processing the next one. In that case, I could imagine not checking the length very carefully and just going to " + " to process the next block -- this would produce the observed "next byte" pointer.

The problem is in the semantics: I said *process* the next block, not *execute* it. If anything this would just cascade into more error cases, since the data that was expected to be the "next block" would almost definitely also have a malformed header (since it wasn't intended to be a header at all), etc.

So, I guess you're right - the tipoff is still that actual code is executed without having to be specifically pointed to (i.e. buffer overrun), and that it's executed in its own thread, rather than taking over the processing thread that was interpreting the metafile in the first place.

Think about it like a programmer

[RingDev (879105)]

Code encounters escape character

exit standard processing

encounter SetAbortProc

open thread to communicate with windows print manager

thread attempts to read [length] bytes for sub value, encounters overrun

this is where I'm guessing the real horrendous problem lies. I'm guessing that the original code ignores exceptions while pulling in the sub value, so in this case where code hits an overrun, instead of that sub value getting a few bytes of data, it just graps until . In this case that sub value winds up being the payload.

So there you go, key and payload on an independent thread because of a bad exception handler in a 12 year old block of code.

-Rick

Re:Length==1

[StarDrifter (144026)]

For me, that length==1 trigger is the most convincing evidence.

It might have been convincing if it were true. The vulnerability checker [hexblog.com] from Ilfak Guilfanov's site uses length==17 to trigger the exploit (Look in the wmfhdr.wmf file in the source zip. The length is a little-endian DWORD at offset 0x12.)

The Metasploit module [metasploit.com] uses a length of 4. Check out the following snippet:

    #
    # StandardMetaRecord - Escape()
    #
    pack('Vvv',

        # DWORD Size; /* Total size of the record in WORDs */
        4,

        # WORD Function; /* Function number (defined in WINDOWS.H) */
        int(rand(256) << 8) + 0x26,

        # WORD Parameters[]; /* Parameter values passed to function */
        9,
    ). $shellcode .

I think Steve Gibson is confused.

Re:Length==1

[atfrase (879806)]

Basically, in the header block for a unit of WMF script contains a "length" field which specifies how long the current unit is. This is standard for this sort of file, and is the primary way to avoid buffer overruns (if you force the data to tell you how big it's supposed to be, and then double check that while reading, you make sure you have enough buffer space to store it all -- otherwise you might read too much, overrun the end of the buffer and trash an important function pointer or something..)

In this case, the smallest possible "length" value is 6, because the header itself takes 6 bytes, so even if the unit had no actual data, the length field itself and the unit's command code is a minimum of 6 bytes.

To trigger the exploit, the length must be set to 1. Not 2, 3, 0, or some other equally invalid value, but only the value "1". Any other value has no effect at all.

do you mean

[by Anonymous Coward]

This Steve Gibson [grcsucks.com] ?, yeah he is a real security expert, along with his podcast boy wonder we have much to be afraid of

Ah, nice Ad-Hominem attack in there...

[Spy der Mann (805235)]

The name means nothing. It's the facts that matter. Whether he is a one-day hacker or some looney, he discovered that for Length==1, (a completely invalid value that makes no sense for WMF's), Windows creates a new thread and starts executing the code.

IMHO your "debunking steve gibson" site is nothing but a smokescreen to divert the attention from Microsoft's vulnerabilities and backdoors.

Re:Ah, nice Ad-Hominem attack in there...

[TheNumberless (650099)]

In my not so humble opinion, you don't know what you are talking about. Go read some of the links in that site, and you'll see that Steve Gibson is one of the many "security experts" that have no clue but gives dangerous and very wrong "solutions".

In my ever-so-humble opinion you completely missed the point of the parent. The reputation, sanity, motives, and anything else dealing with the person making the claim has nothing to do with the validity of the claim itself.

In this particular instance, there is at least some apparent merit to the idea that this was an intentional backdoor, and that merit would be there regardless of who points it out.

If you want to discredit the idea that this is an intentional backdoor (of which I am far from convinced), then you should attack the argument directly, not the man making it.

Possible uses?

[Kitsune78 (941644)]

The freakish thing about this, is that if it is indeed a backdoor, it an odd way to go about it. You can't force someone to try to view a WMF. What would its purpose be? You can't use it to get into the exact box you want to, just into a random box that perhaps picks up your WMF from a webpage, or displayed in an application.

Re:Possible uses?

[RexRhino (769423)]

Digital Rights Management... If you can control a box using a WMF file, there is all sorts of digital rights management mischieve you can do to prevent a machine from copying a file, or decoding a file, or whatever.

Lawsuit time

[Animats (122034)]

Someone involved in a WMA-related lawsuit needs to subpoena, from Microsoft, all the source code and all the change control information for this small part of Windows. Then the original programmers need to be found and deposed under oath. This is standard legal procedure for something like this.

It's possible to get to the bottom of this by legal means.

Magic Lantern?

[Tackhead (54550)]

Sometimes even a blind squirrel gets a nut.

The notion of a backdoor in Windows isn't new. Perhaps the WMF vulnerability was one of the vectors used by Magic Lantern [wired.com], which was the code word for at least one of the FBI's keylogger programs. Magic Lantern was notable in that antivirus providers participated with the Feebs in a gentleman's agreement to not look for it.

It's certainly a dumb enough solution that the IT-challenged FBI might go for it.

On relative dumbness and smartness, I'd expect smart spies, namely those who work for two other notable three-letter-agencies, to use somewhat more interesting techniques. If it were me, I'd take advantage of equipment I had in place at critical infrastructure points to conduct MITM attacks between a PC and Windows Update servers, in order to transparently install my spookware on only those machines that specifically identify themselves - by means of GUID or whatever other stuff I could glean from the Windows Genuine Advantage and other DRM-related bitstreams - as belonging to my target population.

Paranoid? If you're not paranoid, you're not thinking far enough ahead.

Interesting evidence

[joshtimmons (241649)]

I agree with the author that the length prefix is something of a smoking gun. It begs the question of "how do we know it was fixed..." For example, they could change it to execute the datastream when length is set to a new trigger value; or a stronger backdoor would ignore any unsigned code. Still there, but harder to test for.

It's a straightforward way to add a backdoor that will bypass firewalls, etc. It can be triggered by a browsed page, email, etc. It's better than gif/jpeg encoding because those are more "platform independent." and the payload would be more likely noticed by a 3rd party decoder.

On the other hand, isn't this flagged as an attempt to execute code on a data page?

Also, if it were official, doesn't MS have easier ways into a general box - say through security updates, or even the entire existing code base?

Yeah...

[TheAwfulTruth (325623)]

Isn't this the same Steve Gibson that was freaking out about how Raw Sockets in XP were going to destroy the world a couple of years ago?

S.G. is a flaming idiot, he looks for (and imagines) ghosts and spooks in every corner. Then flogs his conspiracy theories to promote himself and his buisness. This probably holds about as much water as the "discovery" of cold fusion and Korean human cloning.

Why aren't we reporting on REAL bugs like the 4 security vulnerabilities found in iTunes this week which opens both Windows and Mac users to external attack? Was the Microsoft bashing quota too low this week?

What is becoming of /.?

Re:Yeah...

[NtroP (649992)]

Isn't this the same Steve Gibson that was freaking out about how Raw Sockets in XP were going to destroy the world a couple of years ago?

Didn't that get quietly fixed in a subsequent update and therefore NOT become an issue? He may be an alarmist, but he's normally a Pro-MS guy. In this case, I think he's on to something.

Who DOCUMENTS their evil backdoor?

[nweaver (113078)]

Who writes an evil backdoor, which dates back to Win3.1 days (when you didn't NEED an evil back door, and Windows had no clue what this Internet thing was about), and then DOCUMENTS it?

Lest we forget that Wine also proved vulnerable, and it was a clean-reimplementation of the specs!

This guy is a moron.

[gregarican (694358)]

I browsed over several posts on his website and come away with the conclusion that he is a few fries short of a Happy Meal. Here's one posting that I found really amusing:

"Thank you Microsoft for blessing us with a patch to fix the products
you currently sell. The products that compete with Linux and Macintosh.
Excellent job at diverting the our attention away from the fact that
Windows 95, Windows 98, Windows 98SE, Windows Millennium Edition, and
Windows NT4 remain vulnerable. Neat trick convincing people that "the
vulnerability is not critical because an exploitable attack vector has
not been identified that would yield a Critical severity rating for
these versions."

Lemme see here. Windows 95 is 11 years old. Windows 98 is 8 years old. Windows ME is 6 years old. And Windows NT4 is 9 years old. How many other operating systems offer patches and support product versions for software that is that old?

Ridiculous.

still in use

[by Anonymous Coward]

The 98 series and NT4 are still in widespread (millions and millions) use. This is called a "problem" then. The auto industry in the US tried to pull this stunt of obsoleting and stopping support for their products in short time frames (sometimes within the SAME model year!) and got legally smacked down for it. Now they are required to provide replacement parts for ten years. Just because normal business productlaws and warranties aren't applied to software-yet, and they certainly should be-doesn't mean it wouldn't be a good idea. Planned obsolesence and forced upgrades might be a spiffy way for some corps to extract a lot more dineros from your wallet, but it doesn't mean it's a good idea for you the consumer/end user...unless you are a pure "caveat emptor" anything-goes styled capitalist. Thankfully, most people see the illogic in that sort of system and that is why we have evolved some consumer protection laws. It is not a perfect solution, but it is light years ahead of legalised snakeoil like it was before. Eventually these sorts of laws will be applied to software,because even the dullest clicker is starting to bingo to the fact that most of this forced upgrade stuff is a cash cow dodge.

Sun and HP for two

[Secrity (742221)]

"Windows 95 is 11 years old. Windows 98 is 8 years old. Windows ME is 6 years old. And Windows NT4 is 9 years old. How many other operating systems offer patches and support product versions for software that is that old?"

I know of at least two. Both Sun and HP still provide support or patches for versions of UNIX System V that are older than Windows 98.

Why hasn't he stepped into the WMF interpreter?

[criznach (583777)]

My question is this... If the guy is smart enough to know that windows has kicked off a thread and executed his code, and he's smart enough to experiment with buffer-overflow exploits, why hasn't he stepped through the WMF interpreter code? Could it be that he doesn't want to admit that he has for legal reasons? I know that if I had discovered this problem, that's just what I would do. Call DebugBreak() and you have a call stack. You'd think that the handler for this SetAbortProc function would be pretty identifiable. So... Who's got the balls (or the time, in my case) to do it? That's our answer. Chris.

Would be a Crappy Backdoor

[ErMaC (131019)]

While the guy makes some good points, there's one point I think he's overlooking. He claims motive for this would be to allow Microsoft or someone else to get into older/current Windows systems as an intentional backdoor...

If that's the case, they chose a dumb place to put it, because the exploit doesn't even work on Windows 2000 and below without some program installed to handle WMF files. From Larry Seltzer's blog (linked from F-Secure):

http://blog.ziffdavis.com/seltzer/archive/2006/01/ 03/39684.aspx [ziffdavis.com]

Except for Windows XP and Windows Server 2003, no Windows versions, in their default configuration, have a default association for WMF files, and none of their Paint programs or any other standard programs installed with them can read WMF files. One ironic point to conclude is that not until their most recent operating system versions did Microsoft include a default handler - the Windows Picture and Fax Viewer - for what has been, for years, an obsolete file format. And now it comes back to bite them.

That means that unless Microsoft used some OTHER backdoor to install a handler for it, this backdoor is useless. I suspect this is merely an oversight on their part, and that it just ends up looking bad when you view it from the outside. The only way to know is to see the source code and well, we know how likely that is.

A real backdoor would be something remotely exploitable via the network, as opposed to hiding inside a file or something like that.

Re:Another?

[dr_dank (472072)]

How about a link to information on the "other" intentional back doors that exist?

*looks at clipboard*

Ok Goatse linkers, thats your cue.

Reflections on Trusting Trust

[Mr Z (6791)]

I'm surprised nobody's trotted out Reflections on Trusting Trust [acm.org], by Ken Thompson. Not only does this discuss a backdoor, but also a backdoor that can't be found by examining the source code.

Re:Another?

[monkeydo (173558)]

Actually, it's pretty well known that that isn't what happened at all [schneier.com].

Re:Another?

[lgw (121541)]

You mean the urban legend [cnn.com] about an NSA backdoor? There was *never* any evidence of a backdoor, only a registry key named "NSAKEY" and a bunch of paranoid fantasy. Because, you know, if the NSA did have a secret backdoor, they'd make sure is was called NSAKEY, in case they forgot where it was, or something.

Re:And this door leads to...

[Tebriel (192168)]

A lawsuit is not the answer to everything.

Re:And this door leads to...

[Anonymous Custard (587661)]

"A lawsuit is not the answer to everything."

Since profit is all a corporation cares about, suing away those profits is the only way to punish it.

Re:Unparalleled BS from MS.

[Soporific (595477)]

I't a lot like the Allied soldiers who were fighting in Germany, being told all these horror stories about how evil the Nazis actually were, and then coming upon a concentration camp and finding out that these stories were real after all.

It's nothing like that actually, you are comparing apples to supernovas.

~S

Re:Unparalleled BS from MS.

[mattbot 5000 (645961)]

It's nothing like that actually, you are comparing apples to supernovas.

It's worse, actually. He's comparing security holes to concentration camps.

Re:You're on

[rbochan (827946)]

Like that'd be a tough thing to do [grcsucks.com]...

Re:Steve Gibson is a crackpot

[Moby Cock (771358)]

Normally I'd agree with you. But in this case I think he may have found something very important. This WMF flap stinks to high heaven. The fact that there seems to be a specific and deliberate key (length == 1) is very disturbing. Gibson is a wacko and doomsayer, but today he may have found something valid.

Re:Steve Gibson is a crackpot

[Rashkae (59673)]

Overlooking that Wine has innadverdantly re-created this 'back door' by following the API spec. This is all by (poor) design, no code back doors involved. Not even a bug, per say, since it's working as designed.

Re:Steve Gibson is a crackpot

[RShearman (740210)]

The Wine bug was a different bug. The SetAbortProc record specifies a pointer to a function which will be executed at a later point, and which it would be difficult to set to arbitrary code in the WMF itself, whereas this bug appears to be creating a thread which immediately runs starts executing the instruction at the next byte in the meta file.

Re:Please not Gibson again...

[NtroP (649992)]

Steve Gibson is not a security expert

I'm not a security expert either. But if I came up with this evidence, how would that change the reality of the situation. The evidence stands on its own merit. His reputation has nothing to do with it. This is easily verifiable by anyone with at least his level of knowledge. It will be interesting to see what happens when other "real" experts start looking at this.