Gatekeerper – A kernel extension to mitigate Gatekeeper bypasses

Security, Tools

Last month Patrick Wardle presented “Exposing Gatekeeper” at VB2015 Prague.
The core of the presentation deals with Gatekeeper bypasses originating in the fact that Gatekeeper only verifies the code signatures of the main binary and not of any linked libraries/frameworks/bundles.
This means it is possible to run unsigned code using dynamic library hijacking techniques also presented by Patrick in code that should be protected by Gatekeeper. His exploit uses an Apple code signed application that is vulnerable to dylib hijacking and his modified to run unsigned code when downloaded from the Internet. In this scenario Gatekeeper enters into action and should verify if the download is code signed (assuming the default OS X scenario where it is enabled). But in this case Gatekeeper will fail to verify the linked code and effectively is bypassed.

The core of the problem is that Gatekeeper only deals with the main binary code, and never verifies any linked code. This is obviously a flaw and hopefully a fix by Apple should be out sooner or later. Meanwhile we can try to build ourselves a fix using the TrustedBSD framework. For this I created Gatekeerper, a proof of concept kernel extension for Yosemite 10.10.5 (can be easily adapted to work with El Capitan, but I don’t want to release that code).
Continue reading →

London and Asia EFI monsters tour!

Mac Reversing, Security, ,

Finally back home from China and Japan tour, so it’s time to finally release the updated slides about EFI Monsters. After Secuinside I updated them a bit, fixing stuff I wasn’t happy with and adding some new content.

The updated version was first presented at 44CON London. I had serious reservations about going to the UK (not even in transit!) but Steve Lord and Adrian charm convinced me to give it a try. 44CON was great and it’s definitely a must attend European conference. It has the perfect size to meet people and share ideas. I prefer single track conferences, dual track is the max I’m interested in. More than that it’s just too big, too messy, too many choices to be made regarding what to see.

A big thanks to everyone at 44CON who made it possible!

Next was SyScan360 in Beijing. It was the fourth time it happened, and my third time in a row. I do like very much to go there because even with language barriers you can feel what’s happening there. Bought a bunch of (cheap) hardware gear made by 360 Unicorn team. Their “usb condom” is super cheap and super small. Also bought a network tap and a USB to serial (don’t really needed it but it was damn cheap). The SyScan360 badge as usual was super fun, this time with a micro Arduino, Bluetooth and LED modules. Conference went pretty smooth and had lots of fun. They had a gigantic LED panel where slides were displayed at. That was some gigantic TV they had there :-)

Big thanks to everyone involved in SyScan360 2015.

Last stop, was CODE BLUE happening in my current favorite city outside Portugal, aka Tokyo. Third time happening, my second in a row. Organization is top notch, everything goes smoothly. Congrats to Kana, El Kentaro, Tessy, and everyone else involved.
This year it had two tracks, and a lot more attendees. It’s definitely a conference to put on your calendar. The audience is super interested in learning. Japan is lagging behind in terms of security so they are keen to finally catch up.

Some people approached me and shown some interested about (U)EFI security. This is great, that was the goal of this presentation, to show people (U)EFI research isn’t that hard and that it is really important its issues start to be fixed. We need to start building trustable foundations and not try to solve everything in software on top of platforms we can’t really trust.

Last conference for the year is No cON Name happening in Barcelona next December.

For next year I already got something that hopefully I’ll be able to present at SyScan360 Singapore. Their CFP is open and you should definitely think about submitting.

There were minor changes between 44CON and SyScan360/Code Blue slides. The latter included more references than 44CON version and minor fixes.

Have fun,
fG!

Slides:
44Con 2015 – Efi Monsters.pdf
SyScan360 2015 – Efi Monsters.pdf
CodeBlue 2015 – Efi Monsters.pdf

Rootfool – a small tool to dynamically disable and enable SIP in El Capitan

Tools

El Capitan is finally released and System Integrity Protection aka SIP aka rootless is finally a reality we must face. Let me briefly describe SIP (technical details maybe in another post, now that El Capitan is final and out of NDAs). This post by Rich Trouton contains a very good description of its userland implementation and configuration.

What is SIP anyway?

The description that I like to use is that SIP is a giant system-wide sandbox, that controls access to what Apple considers critical files and folders. One of the reasons for this is that most of kernel side SIP implementation exists into the Sandbox.kext, the same TrustedBSD kernel extensions that implements OS X sandbox mechanism.

For example, if we try to write to /System folder we get the following result:

sh-3.2# touch /System/test
touch: /System/test: Operation not permitted

And in system logs:

12/10/15 17:27:20,650 sandboxd[120]: ([424]) touch(424) System Policy: deny file-write-create /System/test

In practice it means that even with root access we are unable to modify those critical files and folders.
Continue reading →

Writing Bad @$$ Lamware for OS X

Security,

The following is a guest post by noar (@noarfromspace), a long time friend.
It shows some simple attacks against BlockBlock, a software developed by Patrick Wardle that monitors OS X common persistence locations for potential malware. The other day noar was telling me about a few bypasses he had found so I invited him to write a guest post.
The title is obviously playing with one of Patrick’s presentations. I met Patrick at Shakacon last year and this is not an attempt to shame him (that is reserved mostly for Apple ;-)). It just illustrates the problems of building defensive tools and how much trust you put on them. By personal experience I can tell you that building a security product is a much harder task than what you might think initially.

Disclaimer: we both work for an endpoint software company. Together with another colleague I wrote an OS X version from scratch. I know very well the insane amount of problems that need to be solved, and they never end. When you build something you are always at mercy of potential security problems, we are no exception. Humans make mistakes. Offense is way easier ;-).

Anyway, enjoy it and hopefully learn something new!
Thank you noar!
fG!

I remember those days when there were only 3 or 4 security software editors for OS X. As the threat counts increased, the market grew up too. Many products are now selling you a feeling of being secure: most of them are post-mortem detection tools, and none is re-inventing the security paradigm.

This dinosaur fight left some room for an altruistic new hype: free – but not open source – security tools. Should we trust them blindly?

I am dedicating this post to HGDB, a former colleague and friend. Your sudden departure is leaving us in an infinite sadness. May you rest in peace.

BlockBlock

New utilities are emerging to free the user from major companies subscription fees, like the recently acquired Adware Medic or Objective-See tools KnockKnock and BlockBlock. So I had interest in reversing Patrick Wardle’s BlockBlock, a self-proclaimed continual runtime protection.
Continue reading →

BSides Lisbon and SECUINSIDE 2015 presentations

Papers

I guess my goal for the remaining 2015 of not doing any presentations will not happen.
Two weeks ago I presented at BSides Lisbon 2015 and last week at SECUINSIDE 2015.

I’m very happy to see BSides Lisbon returning after the first edition in 2013. Congrats to Bruno, Tiago, and the rest of the team for making it happen. It’s still a small conference but I’m glad they are making it happen, and I will always do my best to help the Portuguese scene going forward. Everything went pretty well and met some new cool guys. I hope the conference returns in 2016 and keeps growing. Maybe someday it can mutate into something independent of BSides and on its own. Portugal is a great country for conferences, I’m just not the right person to start one, but I’ll definitely help my best anyone who wants to give it a shot.
The presentation is the same as CodeBlue and SyScan since the CFP happened a few months ago. Nothing new in the slides, a fix here and there.

The next was SECUINSIDE in Seoul. This is a very special conference to me because it was the first ever conference I presented at, back in 2012. I never had any plans to ever present at security conferences. I liked my low profile and this blog was good enough to spread the knowledge I wanted to. But I try to be flexible and always open to new adventures, so at the time I accepted HiTCON invitation (they were the first ones) and then SECUINSIDE’s invitation. SECUINSIDE was happening first so at the time I created a different presentation. It was a crazy trip because I did a Porto – Seoul roundtrip, and four days later I went to Taiwan. That was some crazy jetlag!
So this year I went back to SECUINSIDE. Thanks to beist, Ryan, trimo, and everyone else for the great time in Seoul.
The presentation is a new one, made in just a week. It’s essentially an introduction to EFI reverse engineering and hunting for EFI rootkits.

I received yesterday the good news that I was accepted to do the same presentation at 44Con. This is great and I will have enough time to improve the slides. Probably add some new content and tools, since there is good stuff expected out of Thunderstrike 2 presentation.

And here they are:

BSides Lisbon 2015 – BadXNU, A rotten apple!

SECUINSIDE 2015 – Is there an EFI monster inside your apple?

As usual, enjoy and have fun.
fG!

Reversing Prince Harming’s kiss of death

Mac Reversing, Security, , ,

The suspend/resume vulnerability disclosed a few weeks ago (named Prince Harming by Katie Moussouris) turned out to be a zero day. While (I believe) its real world impact is small, it is nonetheless a critical vulnerability and (another) spectacular failure from Apple. It must be noticed that firmware issues are not Apple exclusive. For example, Gigabyte ships their UEFI with the flash always unlocked and other vendors also suffer from all kinds of firmware vulnerabilities.

As I wrote in the original post, I found the vulnerability a couple of months ago while researching different ways to reset a Mac firmware password. At the time, I did not research the source of the bug due to other higher priority tasks. One of the reasons for its full disclosure was the assumption that Apple knew about this problem since newer machines were not vulnerable. So the main question after the media storm was if my assumption was wrong or not and what was really happening inside Apple’s EFI.

The bug is definitely not related to a hardware failure and can be fixed with a (simple) firmware update. The initial assumptions pointing to some kind of S3 boot script failure were correct.
Apparently, Apple did not follow Intel’s recommendation and failed to lock the flash protections (and also SMRR registers) after the S3 suspend cycle. The necessary information is not saved, so the locks will not be restored when the machine wakes up from sleep.

This also allows finding which Mac models are vulnerable to this bug.
All machines based on Ivy Bridge, Sandy Bridge (and maybe older) platforms are vulnerable. This includes the newest Mac Pro since its Xeon E5 CPU is still based on Ivy Bridge platform. All machines based on Haswell or newer platforms are not vulnerable.

Now let’s jump to the technical part and understand why the bug occurs. I am also going to show you how to build a temporary fix.
Continue reading →