CoreText Font Rendering Bug Leads To iOS, OS X Exploit

redkemper writes with this news from BGR.com (based on a report at Hacker News), excerpting: "Android might be targeted by hackers and malware far more often than Apple's iOS platform, but that doesn't mean devices like the iPhone and iPad are immune to threats. A post on a Russian website draws attention to a fairly serious vulnerability that allows nefarious users to remotely crash apps on iOS 6, or even render them unusable. The vulnerability is seemingly due to a bug in Apple's CoreText font rendering framework, and OS X Mountain Lion is affected as well."

Comments

Character-based displays FTW!

[sootman]

I am totally safe.

Re:Who says?

[larry bagina]

The Department of Homeland Security and FBI.

iOS doesn't have exploits

[0xdeadbeef]

It has jailbreaks, and that's a good thing.

Re:iOS doesn't have exploits

[gnasher719]

I thought Apple added address space randomization back in Leopard? What happened?

The problem that was reported leads to a crash. A crash is _safe_. An attacker can't gain any advantage by crashing your computer. They can merely annoy you.

Address Space Randomization cannot prevent crashes. Its purpose is to prevent crashes being turned into exploits. An attacker does two things: Find a way to make your software fail, then find a way to turn that failure into an advantage for the attacker. The second part is where Address Space Randomization comes in. The next step is Sandboxing, where even if the attacker finds a way past ASR and takes over your code, your code would be in a sandbox and can't do any harm outside.

Re:Who says?

[sootman]

Was going to post that but you beat me to it. The details:

Headline: "Four Out of Five Malware Menaces Choose Android"

80%? They make it sound so close! It's actually 100:1 for Android:iOS: "Android was targeted by an astonishing 79 percent of all smartphone malware that year... iOS was targeted by 0.7 percent of malware attacks."

The rest? Windows Phone and BlackBerry, 0.3%; Symbian, 19%.

Re:Who says?

[smash]

Targeted != exploited. They're both targeted, just android is a lot easier to exploit because there is so much junk out there without any updates.

Here's a link to the crasher string in question

[Anonymous Coward]

Here's a link to the crasher string in question:

http://pastebin.com/kDhu72fh

(warning: will crash Safari on OS X 10.8. Firefox doesn't crash.)

Re:Here's a link to the crasher string in question

[Cinder6]

Confirmed Safari crash on 10.8. However, on iOS 7, it does not crash. It looks like this will be patched on mobile within the next couple of weeks. I can't test iOS 6, so I'll take others' word for it.

Re:Who says?

[P-niiice]

The freedom to allow apps permissions for you system brings risks. Read the permissions screen before clicking 'allow', folks.

Re:Le sigh.

[Derek Pomery]

Did you know that TTF fonts are turing complete?
http://en.wikipedia.org/wiki/True_Type_Font#Hinting_language

"It really worries me that the FreeType font library is now being made to accept untrusted content from the web.

The library probably wasnâ(TM)t written under the assumption that it would be fed much more than local fonts from trusted vendors who are already installing arbitrary executable on a computer, and itâ(TM)s already had a handful of vulnerabilities found in it shortly after it first saw use in Firefox.

It is a very large library that actually includes a virtual machine that has been rewritten from pascal to single-threaded non-reentrant C to reentrant C⦠The code is extremely hairy and hard to review, especially for the VM."

http://hackademix.net/2010/03/24/why-noscript-blocks-web-fonts/

Re:Who says?

[ciderbrew]

I do; but its more like ... Find something that looks really good, then look at all the permissions it wants; but it shouldn't need all those permissions!! Feel sad about it and then don't install it unless drunk.

Good thing Slashdot doesn't support Unicode!

[Anonymous Coward]

Otherwise someone would post it in the comments here and crash iPhone users' browser!

Re:Who says?

[Joce640k]

Well that would be logical wouldn't it, given that Android is a more widely used platform

Not only that, it has a checkbox to allow you to install unsigned apps from uncontrolled websites.

Unsurprisingly, bad people upload malware to those sites. If you download it and click "yes", you'll get what you deserve, just like installing randomly downloaded exe files on PCs, etc.

Re:Who says?

[Anubis IV]

Secure? Maybe, maybe not. Having less malware does not mean something is more secure, after all. More safe? Definitely so, since having less malware means that there is simply less danger. A walled garden in the country side is more safe but less secure than an apartment with bars over all the windows in the middle of the city, after all, and safety is what is more important overall, rather than security.

Of course, that doesn't excuse a company to fail at securing their products, just because no one has attacked them yet, but by all indications, the "security through obscurity" argument doesn't hold much water in this case, given that iPhone users are consistently shown to be disproportionately profitable to target and that they continue to sell extremely well overall (even the report you linked cites the fact that this is an expected low as part of the regular product cycle for the line and that they expect the iPhone to recapture its lost market share with the launch of the new iPhone this quarter).

Long story short, Android appears to be less secure and less safe. Which is to be expected, given the fact that developers are able to do a lot more on Android than they can on iOS, so it's not without its upsides, by any means. But that added capability (and the fact that every carrier/manufacturer makes their own tweaks that can open up vulnerabilities) comes at a price, and in this case, it's security.

Re:Le sigh.

[iluvcapra]

Desktop publishing has used embedded, Turing-complete languages for decades -- TeX is Turing-complete, as is XSLT. It's the best and most compact way of specifying an abstract image for a generic rasterizing displays of arbitrary resolution.

Re:Who says?

[0123456]

Right, because having users manage their own risk profile has worked out so well in the PC/Windows world...

Indeed. Letting someone else control your computer is much safer.

Android's big problem is that you have no way of saying 'no, I'm not giving this app that permission', and can only choose to install or not install the Fluffy Kitty Screen Saver that wants access to your filesystem, the Internet, and the ability to send SMS messages.

Re:Who says?

[chowdahhead]

I think Android is targeted more because it isn't inherently tied to the Play store, and not so much because of devices not being updated. The app signature verification works for 2.3 and up, which covers 96% of Google's Android devices. Getting malware on a phone or tablet still generally requires installing a malicious app, and it's far easier to be careless about that on Android.

Re:Who says?

[RoboJ1M]

Agreed.

It's the same as Windows, you just target what gets you the largest return. Organised crime is a business, just like any other.
However there is still the walled garden thing, even if Apple went back up to a 50:50 market share with Android, Android would get targeted more because every Android user can choose to install any application and give that app the permission to email their bank details to Russia.

With iOS they have to wait for a good ol' fashioned buffer overflow before they can grab anything I guess.
Unless you get that with iOS too? I don't know I've never owned one.

But the 8:2 logic holds up, when the sample size it that large I'm guessing that's exactly the reason why.

Ultimately it's all moot.

If Apple had 100% of the market share this is what would happen:

The crims would send everyone sms/emails with links to pages that asked them for their passwords an X percent of users would give it to them.

No amount of security or walled gardens get around the fact most of you are really really thick.

You don't have to install Cute Kitty Wallpapers with internet, sms and bank details access.
Because that's all this "malware" is, it's not big or clever, 50% are just from the wrong side of the bell curve.

Oh, an I use Linux.
On the Desktop.
Well, I used to, because who the hell uses a desktop anymore anyway?
Have you seen this cute screensaver I found!!!

Re:Le sigh.

[VortexCortex]

Okay, am I the only one that thinks that if you can't design something that renders text onto a screen without it turning into the Ocean's Eleven of computer security, you're doing it wrong? Be honest now guys. I can understand this in something that needs to interpret complex animations of dancing toilet paper flying across my screen screaming "Buy meeeee, pleeeeeeease!" -- I don't approve, but I can see how someone could screw it up.

But text... really guys, I mean, really?

I really get where you're coming from... However, Unicode is a PITA to implement, what with multiple glyphs for compositions / decompositions and BIDI (text direction rules) -- which change depending on paragraph direction and state machine. That's just the character encoding! To actually render the fonts there's a tiny VM that decodes the glyphs and handles sub-pixel hinting, etc. A bitmap ASCII (CP437) font? Done. I can crank one out in an hour, tops... Unicode w/ TrueType or FreeType? Ugh. I mean, just getting the character property tables from the Unicode site downloaded and transformed from CSV to the format we need is a project in of itself. The bugs in every last 3rd party library ever encountered (even libPNG), I'm hesitant to use other's code unless I have to (I have a higher standard -- input fuzzing, code coverage and unit testing for everything), but bugs in today's text rendering systems aren't just expected, they're a given -- It's literally the first thing I attack, and almost every time it works against new code: embedded invalid surrogate pairs, and over-long forms.

Ah, but everyone's doing it wrong but you? Well, let me tell ya something: If you set out to make the closest to the metal compilable language that's not ASM, it'll work just like C does (C is a product of the architecture more than anything). Same goes for making a minimal font rendering system that covers all the world's languages -- Try it, it'll end up almost exactly like TrueType & Unicode because they're products of their environment too.

Now, that's not to say I don't agree with you to some extent. I'd say humans need to ditch all the BS and start from scratch to create a language that's easy to OCR with syntax and grammar that's extensible and non ambiguous and thus interpretable by machines. Do that and "natural language processing" is a no-brainer (literally). We get away with as few as 16 glyphs for the Virgon (Galactic) language -- Designed for ease of deciphering from examples using mathematics, incrementally graduating up to a small Von Neumann "VM" and then including "instructional" programs to then teach the rest.... So, yeah, you damn dirty apes did do it wrong, but if your sunk cost fallacy doesn't keep you doing it wrong you'll be the first lifeforms in the Super Cluster to do it right before you've solved the Fermi Paradox.

The myth of the equal opportunity attacker

[benjymouse]

Holy cow, your fanboy hat must be cutting off the flow of blood to your brain. Explain again why an OS with 4x the market share garners 100x the exploits?

Attackers will *always* try to attack the biggest target. They are not for equal opportunity, they do not meet to work out quotas so that OSes gets attacked accordingly to their market share.

Say you joined a shooting competition: You can shoot at two targets, equal size and equal distance, no objective difference at all. Only difference is that each time you hit target A four people will give you $10 each and each time you hit target B only one person give you $10. You have 10 rounds. How do you distribute your rounds between the two targets? Do you fire 8 shots at target A and 2 shots at target B because that would be the most fair thing to do, or do you fire all 10 shots at target A?.

Maybe, just maybe, there's more to it than market share.

There might be. When you see people start taking shots at B, despite the higher reward of hitting target A, you can conclude that some factor causes them to *not* go for the higher reward. Somehow target A must have become harder to hit, the reward is going down or the shooters skills allow them to hit target B more easily.

But all other things being equal, prudent attackers who are in it for the rewards will go for the higher market share, every time.