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Not enough people seem to know about JTAG outside the hacker and LEO communities but the short version is that JTAG allows anyone with physical access to your phone to chew their way right into it.

I can't understand why fundamentally disposable mass market consumer devices need a working test instrumentation port when they are released to the average consumer; In my opinion this is a significant security vulnerability across the entire Android ecosystem.

--- Added This is not an issue of whether or not the device is secure - it is an issue of whether or not the presence of a functional JTAG interface significantly alters the cost/reward equation for lower value data for a less experienced attacker. Evaluating security risk involves evaluating the costs and risks of compromising a system - there is no system that is completely secure against anything, and a system that is secure against nothing is worth nothing (in this context) (e.g. your phone broadcasts its memory over open wireless all the time) - my concern is that a working JTAG port on a device with 'interesting' data on it is signficantly weaker than one without such a port and therefore the cost/reward equation is significantly changed

--- Added Citation Editor’s note: JTAG is a well-known standard mechanism for in-field test. Although it provides high controllability and observability, it also poses great security challenges.

This article analyzes various attacks and proposes protection schemes. Mohammad Tehranipoor, University of Connecticut - citation -

makerofthings7
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Mark Mullin
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  • Go look at a Bus Pirate. You don't need ports to extract information. Basic answer is, "Don't lose your phone". If you're that important and you've put delicate information on it in an unencrypted state, it's free for anyone with technical expertise to extract. – Fiasco Labs Oct 06 '12 at 02:07
  • The question is the level of technical expertise - JTAG renders MDM (http://en.wikipedia.org/wiki/Mobile_device_management) pointless – Mark Mullin Oct 06 '12 at 02:11
  • @MarkMullin: So does unrestricted physical access to the phone. – Scott Pack Oct 06 '12 at 15:51

3 Answers3

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No.

There's something to be said for the fact that if you "own" a machine, then you own it. Physical possession of a piece of hardware with the ability to disassemble, modify, and otherwise physically hack the device very nearly guarantees that with enough work you will be able to get around security measure that might be present.

So, no, JTAG is no more troublesome than a USB port, or exposed RAM leads, or a desolderable flash chip.

EDIT

I can't understand why fundamentally disposable mass market consumer devices need a working test instrumentation port

JTAG is useful for more than just development testing. It's also used by repair technicians to fix phones that have firmware damage that makes software-based tools unusable. Including JTAG support in the production device lowers the maintenance/repair cost to the carriers who tend to be responsible for maintaining and fixing these devices on behalf of the customer. And lowering cost is always a worthwhile goal for the provider.

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tylerl
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  • I agree - but this makes your phone as easily breachable by someone else as it makes it by you - I like the idea of being able to buy a phone with working jtag, i do not like the idea of companies making their byod plans radically insecure by not even knowing this risk is present - it's basically reducing the cost of an attack by an unreasonable level – Mark Mullin Oct 05 '12 at 23:46
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    @MarkMullin You cannot protect a device that is in the attacker's physical possession. That's the beginning and end of it. If you want to keep your data safe, the only way (**only** way) is to encrypt it. If cutting the JTAG traces gives you a warm fuzzy, then go ahead and do that. But it will not give you the security you care about. – tylerl Oct 06 '12 at 00:17
  • @MarkMullin Number 3: http://technet.microsoft.com/en-us/library/hh278941.aspx – ewanm89 Oct 06 '12 at 00:27
  • @tylerl True -the lack of physical security is no security at all - the issue is the cost of the comprimise - if it requires a chip off attack, then the cost is much higher than this - a relatively inexperienced individual can comprimise a device through a JTAG port without being able to remove a BGA chip with a heat gun, have any kind of ICE equipment, etc - I'm not concerned with the possibility, it's the ridiculously low barrier to entry that bothers me – Mark Mullin Oct 06 '12 at 00:48
  • @tylerl as far as device repair - other than screen replacement I'm not aware of much of that happening - and encryption is only a guarantee in this case if all data is truly encrypted/decrypted on each access from an externally entered key - last I checked ARM chips are going to be a bit challenged if I use decent encryption against several gigs each time i log in or out - i wont argue wear leveling analysis, cause that is back in the domain of the rarer black hats and a risk one just has to deal with – Mark Mullin Oct 06 '12 at 00:52
  • @ewanm89 - I'm well aware of that - but a lot of security involves the balance of information value against attacker workload - my issue here is that the JTAG port removes most of the workload on the attacker - thats what I don't like, not the fact the device can be comprimised – Mark Mullin Oct 06 '12 at 00:56
  • _Law #3: If a bad guy has unrestricted physical access to your computer, it's not your computer anymore._ And if it doesn't have an automatic self-destruct on opening the case, you can prod it in any number of ways to get it to spill information. – Fiasco Labs Oct 06 '12 at 02:10
  • Granted - some blackberries have exactly that after a fashion - pull the cover off, memory gets zero'd - and I'm fine with that - beating that raises the penetration cost back to a reasonable level - this is not an issue of how horrible, it's a question about cost and risk – Mark Mullin Oct 06 '12 at 02:34
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    Never underestimate the reduction of support costs that a JTAG port brings. On old phones, a reflash of the baseband firmware required test points to be connected, which were essentially tiny SMT pads on the phone board. This meant that the entire phone had to be dismantled, and a special set of connectors had to be attached (and usually held in place by hand). Also keep in mind that each manufacturer's testpoint was a custom piece of hardware that hooked up to a PC's serial port, or USB if you were lucky. As such, they cost thousands to buy. Factor in added manual work... very costly. – Polynomial Oct 06 '12 at 09:40
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    As an example, the phone unlocking shop that I used to work in could do a baseband flash on a [Motorola Razr v3](http://en.wikipedia.org/wiki/File:Razor2000ppx.jpg) in about an hour, or a Blackberry Bold in about 20 minutes. JTAG made all the difference - less than half of those 20 minutes were spent actually hooking up the phone to the JTAG testpoint, the rest was just the firmware upload and reboot. On the old Razr V3 it took ages to strip the phone down to just the board, and hook it all up. Plus we'd frequently have problems with cracked plastic and other damage during the process. – Polynomial Oct 06 '12 at 09:44
  • @Polynomial I grant the value of JTAG - my concern is exactly what you point out - the ease of unlocking and reconfiguring it - my concern is for impacts on security in business applications - ypu've hit the point thats bothering me right on the head – Mark Mullin Oct 06 '12 at 13:05
  • But that's *precisely* the point that this answer covers. It's [Immutable Law of Security #3](http://technet.microsoft.com/en-us/library/hh278941.aspx) - if the bad guys get physical access to your device, it is no longer your device. – Polynomial Oct 06 '12 at 13:23
  • @polynomial - true, but that law is a simplistic overgeneralization - consider bank vaults - they come in many flavors, and the ones used by the New York Fed are considerably more sophisticated than the one used in a small town - you have to address the fact that IFF the bad guys get a hold of something, how much does it cost them to get in and try and ensure cost beats exploit value- otherwise the argument would be that there is no point in security beyond physical security (strictly limited to the context of this discussion) My concern here is focused on the cost & record of comprimise – Mark Mullin Oct 06 '12 at 15:36
  • @MarkMullin While I fully understand your point, I don't think you're going to get anyone here to agree with you. – tylerl Oct 06 '12 at 18:35
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    @MarkMullin You're missing an important caveat of the rule - a safe is *not* designed to prevent any form of access. If you have the tools and the time, you can *always* break into a safe. The goal of the safe is to make it time consuming and infeasible to break into it without being caught in the act. If you have unrestricted access to the safe, e.g. if you can put the safe in a 600 tonne machine press, it is just as pwned as an Android device that you hand to a bad guy. The JTAG issue is the same thing - given unrestricted access you're pwned *no matter what*. – Polynomial Oct 07 '12 at 00:09
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    @tylerl I don't agree with the statement that it's impossible to "protect a device that is in the attacker's physical possession." It's extremely difficult and expensive - but not impossible. Any FIPS 140-2 security level 4 device is supposed to be secure even if it's in the attacker's physical possession for a substantial amount of time (this includes many HSMs). A good example is the PS3, which was in the attacker's hands for four years before its DRM was hacked (see http://events.ccc.de/congress/2010/Fahrplan/attachments/1780_27c3_console_hacking_2010.pdf). – David Wachtfogel Oct 07 '12 at 05:55
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It depends on the device. In most Android devices it is possible to physically replace the software in Flash (the so-called "ROM") and thus overcome any software dependent security, in which case an open JTAG port doesn't make things much worse. But there are a few Android devices on the market in which the hardware validates the "ROM" software before it is loaded. In such devices it's critical that the JTAG be locked as well. I suspect this is the situation in Android devices approved by the US Department of Defense.

In a comment you mentioned the ARM TrustZone technology. One of the feature of TrustZone is that resources (e.g. code, data) protected by the ARM TrustZone are inaccessible to a JTAG port even if there is an open JTAG port on the device. In other words with TrustZone you can have an open JTAG give you access to most of the device resources but not to the most sensitive resources which are protected by TrustZone.

David Wachtfogel
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  • OK, I do think JTAG makes things worse, but if you're alluding to a pure software exploit I can't argue - and they're out there - far as I'm concerned, this means any line of business application with deep offline functionality cannot be considered to impose any reasonable breach cost - I can't deny I am becoming ever more horrified by security understanding in general tho - to paraphrase Eliot - security is not black and white, it is endless shades of gray once you leave the clean world of modern algebra – Mark Mullin Oct 06 '12 at 22:15
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    Very true. Regarding pure software exploits, Android is getting much harder to break thanks to ASLR and DEP (see http://arstechnica.com/security/2012/07/android-jelly-bean-hard-to-exploit/) and the next line of attack for someone with physical access to a device would likely be JTAG. – David Wachtfogel Oct 07 '12 at 05:40
  • You can debug the TrustZone secure world through JTAG too. But if the manufacturer did things properly, that possibility will be disabled or at least require cryptographic authentication on a non-development device. – Gilles 'SO- stop being evil' Dec 31 '12 at 14:59
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What bothering me is that people are managing valuable data -- in some cases, their whole life, and some other data which was entrusted to them -- in devices for which they cannot, do not, and not even try to, maintain physical security. A phone is something which is:

  1. expensive;
  2. small enough to be easily carried, but large enough to allow for easy grasping;
  3. brandished by the users while walking in the street, secured in position mostly by the suction strength of their ear, while the user is distracted by a conversation, and thus does not pay attention to his/her immediate environment.

It is no wonder that mobile phones are the most often stolen kind of object. A mobile phone is a risk by itself.

That the thief will be able to access the data without scratching the case, well, it does not bother me.

Thomas Pornin
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  • Granted - but now they're bringing these devices into corporate networks on 'Bring your own device' (BYOD) programs, and the companies are installing 'Mobile Device Managers' (MDMs) that are supposed to protect the companies data - and this makes any of that protection a complete illusion - my issue is that with the existence of the JTAG port, any effort to secure the device is fundamentally pointless - no software can protect you against chip/instruction level access - and it isn't that they don't scratch the case, they can give it back to you and there's NO way to tell they were there :-( – Mark Mullin Oct 06 '12 at 00:20
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    @MarkMullin I think what you're not getting is that securing the device against an intruder who has physical access is a fundamentally pointless endeavor and an illusion to begin with. Adding a JTAG port does not decrease the security as there was none to begin with. – tylerl Oct 06 '12 at 00:34
  • @tylerl See http://www.arm.com/products/processors/technologies/trustzone.php - you can buy a samsung galaxy 3 in europe that has this, but you can't buy one here - as i said above, the concern i have is not that it is possible, it is that the jtag port removes most of the workload on the attacker - if someones going to peel the chips off the board there's not much i can do - what i don't like is someone with far less skills being able to mount the same attack - i can never protect the secret molecule on a drug ceo phone - but now I can't protect a local cops notes either – Mark Mullin Oct 06 '12 at 01:02