[INFO] Understanding the risks of having an unlocked bootloader

[Petrovski80]

While unlocking the bootloader on a Galaxy Nexus unleashes the full potential of the bootloader, it also poses a security risk. Even with your lockscreen protected with a pattern/PIN/password, not having flashed a custom recovery, having an anti-theft app installed (maybe even converted/installed as a system app) your phone's data is easily accessible for a knowledgeable thief.

All the thief needs to do is reboot into the bootloader and boot or flash a custom recovery such as ClockWorkMod or TWRP. It's then possible to boot into recovery and use ADB commands to gain access to the phone's data on the internal memory (unless you have it encrypted) and copy/remove files at will.

Granted, the risk seems low. The thief would not only require knowledge of fastboot, he would have to turn off the phone before you have issued a wipe command using an anti-theft app. You could of course flash back the stock recovery & relock the bootloader after being done with flashing stuff, but that would require you to unlock it again if needed which will erase your userdata.

There are two ways to tackle this security risk AND retain unlocked bootloader functionality without losing userdata.

1) Encrypt your phone using Android's built-in encryption feature

Advantages:
- you can leave your bootloader unlocked & leave a custom recovery installed without risk of exposing your data.

Disadvantages:
- unless the custom recovery can decrypt your phone, you cannot use all of its features.
- when decryption fails, you cannot access your phone and need to do a factory reset from recovery. Users have reported not being able to decrypt after applying OTA updates.
- the encryption process is irreversible. The only way to return to an unencrypted phone is to perform a factory data reset which erases all your data.


2) Unlock & relock the bootloader from Android OS

Prerequisites:
- root access
- an app that can unlock/relock the bootloader at will such as BootUnlocker

Steps
Root your device using one of the many guides out there (recommended guide). Install BootUnlocker. Reflash stock recovery and lock the bootloader. Whenever you need an unlocked bootloader again, simply use Bootlocker to unlock it (this won't wipe userdata). When done, relock.

Advantages:
- doesn't require encryption (for those who do not wish to use it).

Disadvantages:
- relies on third-party apps.
- method will not work if you lose root access for whatever reason.
- method will not work when you cannot boot into Android for whatever reason.


USB debugging
Strictly not related to the bootloader, but for maximum security disable USB debugging when not required. Having it enabled allows the execution of ADB commands even if the lockscreen is still locked. Myself, I use Tasker in combination with Secure Settings to automatically enable USB debugging when my device is connected to my home WiFi access point but disabled if not connected.

The following video demonstrates what a knowledgeable thief can do with your phone when you have USB debugging enabled by default: http://www.youtube.com/watch?v=ah7DWawLax8&t=7m0s

More info: recently, an exploit has been discovered that will enable gaining root without going through the 'traditional' process of unlocking the bootloader & flashing a custom recovery in order to flash Superuser or SuperSU packages. See this post for a guide.

Play store devices
Devices bought directly from Google's Play Store apparently do NOT wipe userdata after fastboot oem unlock. So for these devices, method number 2 does not add any security. For more info, read this thread: http://xdaforums.com/showthread.php?t=1650830

 

[efrant]

Very well written!!

One thing you may want to tie in to your explanation is the effect of having USB Debugging enabled - it's easy to gain root (and subsequently unlock your bootloader) with it enabled, even with a locked bootloader.

Sent from my Galaxy Nexus using Tapatalk 2

 

[Petrovski80]

Added some information regarding USB debugging. Thanks for the tip efrant.

 

[Mach3.2]

Good read:good:

 

[Oscuras]

Do you have to be on stock rom to lock the bootloader ?

 

[efrant]

Do you have to be on stock rom to lock the bootloader ?

Nope.

Sent from my Galaxy Nexus using Tapatalk 2

 

[Guiding.God]

Thanks for this :good:

Trying to wrap my head around this with regards to anti theft protection etc.

Currently have an unlocked bootloader, custom rom, and root. If I have something like Cerberus or Avast running (both claim to work as system apps so will not be deleted via hard reset), have debugging unchecked and a pin lock at screen on - if I lock bootloader now, how secure am I to data theft?

Presumably, with debug disabled, fastboot from pc command prompt to unlock bootloader will not work? Can ODIN be used to flash a new ROM and if so my system apps (and thus the security apps) will be wiped, rendering the whole thing useless?

Thanks

 

[Petrovski80]

Thanks for this :good:

Trying to wrap my head around this with regards to anti theft protection etc.

Currently have an unlocked bootloader, custom rom, and root. If I have something like Cerberus or Avast running (both claim to work as system apps so will not be deleted via hard reset), have debugging unchecked and a pin lock at screen on - if I lock bootloader now, how secure am I to data theft?

Presumably, with debug disabled, fastboot from pc command prompt to unlock bootloader will not work? Can ODIN be used to flash a new ROM and if so my system apps (and thus the security apps) will be wiped, rendering the whole thing useless?

Thanks

If you have the stock recovery (custom will allow adb), your personal data is as secure as it can be. Of course, you cannot stop anybody from booting into your bootloader and run fastboot oem unlock OR use Odin to flash your device. However, doing so will effectively wipe your device so your personal data cannot be accessed.

 

[qtwrk]

I would more worry about my phone then data because I have nothing important on it...

Sent from my Galaxy Nexus using xda premium

 

[Guiding.God]

If you have the stock recovery (custom will allow adb), your personal data is as secure as it can be. Of course, you cannot stop anybody from booting into your bootloader and run fastboot oem unlock OR use Odin to flash your device. However, doing so will effectively wipe your device so your personal data cannot be accessed.

I would more worry about my phone then data because I have nothing important on it...

Sent from my Galaxy Nexus using xda premium

Thanks for the clarification.

And I worry more about the work related data, the phone itself is insured

 

[mrphil101]

This is important info, and a lot of folks probably don't realize how open they are. This should be stickied or better yet included in the stickied thread where the bootloader unlock instructions are. Thanks for the post.

 

[Pkt_Lnt]

Great info. One question, I use Titanium Backup automated nightly to backup data and new apps, and it requires USB Debugging on.

I suppose I could use Secure Settings to turn USB Debugging on and off, but that means an opening is available once a day for a few minutes. Thoughts?

 

[Petrovski80]

Great info. One question, I use Titanium Backup automated nightly to backup data and new apps, and it requires USB Debugging on.

I suppose I could use Secure Settings to turn USB Debugging on and off, but that means an opening is available once a day for a few minutes. Thoughts?

You could do as I do: use secure settings in combination with tasker so USB debugging will only be enabled when connected to your home Wifi. It will allow your nightly TiB backups, and I assume the 'ADB opening' is not an issue when at home (not many thieves there I hope).

 

[Pkt_Lnt]

You could do as I do: use secure settings in combination with tasker so USB debugging will only be enabled when connected to your home Wifi. It will allow your nightly TiB backups, and I assume the 'ADB opening' is not an issue when at home (not many thieves there I hope).

I downloaded Secure Settings to check it, and it will work. I have AutomateIT Pro and it does not support plug-ins. I have been finding more tasks that it seems only Tasker can perform, I guess it is time to get it. Thank you.

 

[strumcat]

You could do as I do: use secure settings in combination with tasker so USB debugging will only be enabled when connected to your home Wifi. It will allow your nightly TiB backups, and I assume the 'ADB opening' is not an issue when at home (not many thieves there I hope).

Great idea.

 

[Cilraaz]

You could do as I do: use secure settings in combination with tasker so USB debugging will only be enabled when connected to your home Wifi. It will allow your nightly TiB backups, and I assume the 'ADB opening' is not an issue when at home (not many thieves there I hope).

A Jasager router could exploit this if you have WiFi enabled in public. When WiFi is enabled and not connected to a network, every 'x' period of time (depending upon your wifi.supplicant_scan_interval setting in your build.prop) your phone will send out a packet saying "hey, is xyz network around?". It will do that for every network that you have saved settings for.

Under normal circumstances, you get no reply when away from your home router and the phone just waits the interval to try again. A Jasager ("yes man" in German) router waits for a device to send out those packets and simply responds "yep, that's me!". Under this circumstance, your phone would authenticate to their router and think it's on your home network, triggering any applicable Tasker options.

This is one of the reasons that I do not have WiFi enabled unless I actively want to be connected to a router in the area.

Also, I have USB Debugging disabled and my TiBu backups run perfectly fine according to schedule.

 

[blackhand1001]

I am not a paranoid worry wart so the risk are more than worth it for me. There's nothing on here that I would care if some one got a hold of anyway.

Sent from my Galaxy Nexus using xda premium

 

[Petrovski80]

A Jasager router could exploit this if you have WiFi enabled in public. When WiFi is enabled and not connected to a network, every 'x' period of time (depending upon your wifi.supplicant_scan_interval setting in your build.prop) your phone will send out a packet saying "hey, is xyz network around?". It will do that for every network that you have saved settings for.

Under normal circumstances, you get no reply when away from your home router and the phone just waits the interval to try again. A Jasager ("yes man" in German) router waits for a device to send out those packets and simply responds "yep, that's me!". Under this circumstance, your phone would authenticate to their router and think it's on your home network, triggering any applicable Tasker options.

This is one of the reasons that I do not have WiFi enabled unless I actively want to be connected to a router in the area.

Also, I have USB Debugging disabled and my TiBu backups run perfectly fine according to schedule.

Maybe. Tasker checks both the SSID and the MAC address of my router before it returns 'wifi connected' as true and enables USB debugging. Sure, MAC addresses are easy to spoof, but I don't think the MAC address is part of the broadcast packet (I haven't checked) because that's simply a value stored by Tasker itself.

And even if it is, the combination of a lost/stolen GNEX and a thief who modded their router with jasager firmware + knows ADB is too unlikely for me to worry about it. But indeed, for maximum security it's best not to automate enabling of USB debugging.

 

[Cilraaz]

Maybe. Tasker checks both the SSID and the MAC address of my router before it returns 'wifi connected' as true and enables USB debugging. Sure, MAC addresses are easy to spoof, but I don't think the MAC address is part of the broadcast packet (I haven't checked) because that's simply a value stored by Tasker itself.

And even if it is, the combination of a lost/stolen GNEX and a thief who modded their router with jasager firmware + knows ADB is too unlikely for me to worry about it. But indeed, for maximum security it's best not to automate enabling of USB debugging.

The MAC check would almost certainly keep you safe.

It's interesting stumbling across this thread after having just seen a podcast episode about Android hacking. If anyone is interested, check out Hak5. One of their recent episodes is about Android hacking via ADB, specifically something called P2PADB that was created for quick device-to-device ADB access. It was fairly amazing the things this person could do to a phone that has USB Debugging enabled.

 

[Petrovski80]

The MAC check would almost certainly keep you safe.

It's interesting stumbling across this thread after having just seen a podcast episode about Android hacking. If anyone is interested, check out Hak5. One of their recent episodes is about Android hacking via ADB, specifically something called P2PADB that was created for quick device-to-device ADB access. It was fairly amazing the things this person could do to a phone that has USB Debugging enabled.

Watching the video right now. Personally, I find it a gaping security hole that the ADB interface is accessible through a locked lockscreen.

For anyone interested in the vid: the ADB part starts at 7:00.

Edit: amazing video. It really proves what a knowledgeable thief can do when you have USB debugging enabled, especially when combined with root access (don't we all?). I'm going to add the video to my post. Thanks for the info Cilraaz!