Pratique du Shadowing: Watch this before you boot up another device - Apprendre l'anglais à l'oral avec la vidéo

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Ladies and gentlemen, boys and girls, lend me, lend me, lend me your ears.

I want to show you this really neat vulnerability in U-Boot that everyone's talking about.

Not everyone, but I am.

So if you run the script here, QEMU drive, QMU, bada bing, bada boom, you will see the magical values.

The 41414141, the 41414141, and the 4242423E.

What the hell is even going on?

What are we talking about?

Guys, we're talking about a vulnerability in U-Boot,

the bootloader that allows you to bypass signature verification by exploiting a vulnerability in the bootloader itself.

Bugs like this are really, really neat because they actually invalidate an entire trust chain in the way that weird devices like this, like embedded ones and even ones that you sit in your pocket,

validate if they use U-Boot.

Obviously, this one does not.

This one might.

Anyway, I'm going to break down the bug, what went wrong, what you can do about it, and then also what the hell all this stuff means.

The finding today was found by a company named Binarly.

I've done videos on their stuff before.

They do a really good job on finding vulnerabilities in like lower level.

That's the name of the channel, by the way.

Low level.

Low level systems like bootloaders or BMC, board management controllers, stuff like that.

Again, not an ad for this company, just they do a lot of good work.

So the vulnerability today is a stack buffer underflow, kind of hard to say, in uBoot during the FIT image signature verification,

specifically in the FDT find regions functions.

A lot of words said there.

I'm gonna go into what all that means here in a little bit.

Okay, so enter uBoot, right?

What is uBoot?

Well, uBoot, kind of like the name of this folder that I had, I called it Das Boot.

uBoot is a system that allows you to, in an embedded world, boot other OSes, right?

So typically, the way these weird devices work is you have to bring them up.

You gotta get the board to be alive, you have to bring the CPU to live.

And then the first thing that you run on a router like this is this thing called a bootloader.

A bootloader is a piece of code that allows you to run other code.

The idea being, you don't have to make that piece of code know how to boot against every other CPU.

You just bring the CPU up to the bootloader, and the bootloader does the rest of the work, right?

You can use that bootloader to run your OS, like Linux or Windows or whatever.

So if the job of the bootloader is to run code that we want it to run, why does RCE in a bootloader matter?

Why does the vulnerability in U-Boot matter to anybody?

Great question.

What actually is interesting about U-Boot is its ability to facilitate this thing called verified boot, okay?

There's this whole world of boot processes

that the entire job is to make sure that code

that is not meant to be ran does not run on the device.

And we do this thing where we use a bunch of cryptographical algorithms using asymmetric encryption with like RSA keys

and public keys and stuff to sign the software image before it tries to get loaded.

And then using a public key on the device, we verify if that manufacturer signed image is actually what we want.

Is it the proper thing that is allowed to run on this device?

because maybe we just don't want anyone to be able to

run any software they want on random piece of Chinese router, right?

Maybe that's a thing that they don't want.

Okay.

So the issue that happens here is when you go to boot with a U-boot image in this fit format, this flattened image tree format,

it is signed with a signature.

It is basically taking a private key that the manufacturer owns.

We use that to embed a signature cryptographically that says, yup, it was signed by this manufacturer.

And then we use the public key on the device to verify the signature

that it was manufactured and it is the proper image.

But we can invalidate this entire signature verification process.

We can upload and execute a piece of code that is not intended by the manufacturer

if we can find and exploit a vulnerability inside of the bootloader.

And this is exactly what Binarily did.

And I'm sorry if you're worth with Binarily and I'm mispronouncing the company's name.

I'm not very good at English.

Okay, so stack buffer underflow in uBoot during the FIT image signature verification and FDT find regions.

Basically, there's code in the bootloader that is finding different regions of the actual image itself.

And the vulnerability is based on the same issue as one above, where we rely on the fact that FTT getName, which is a call that happens above, can fail.

But this time we're interested in what it writes to the length argument upon failure.

The error code.

Very interesting.

So there's this function called FTT getName, that if for any reason in this searching of the image during this FTT getName process,

where it's getting the name of a leaf of this image format, right?

If for some reason it's searching and it finds that one of the leaves does not have a slash, right?

So strrcare is a thread-safe version of strcare, which basically looks for a token in a string.

If that fails, we set error equal to some value and we go to fail.

And then in the fail label, we say if the length pointer exists, we are going to write out that length pointer, which should be the output of the actual length of the name.

Instead, we're going to output an error value, and that error value is FTT error bad structure.

And then notice that later on in the code we're going to do is we're going to say start copy onto end, the name that we found from that function, oh, and also end plus equals length.

Well, the issue here is that length holds a negative value.

It is a large negative error code.

So instead of actually moving the end of that cursor of parsing forward, the pointer moves backwards.

It'll go backwards by the size or the value of error bad structure, which is negative 11th.

And then it will increment that and add a slash.

As the amount of code generated by AI increases, one thing that scares me is the ability to maintain that volume of code.

And that's why today's video is sponsored by CodeRabbit.

CodeRabbit is an AI code review tool that helps engineers manage the world of AI generated PRs.

For one of my platforms, Lillava Labs, I added a feature to add bookmarks to the site, right? a fairly simple feature, but adding new API endpoints like anything does create potential new security vulnerabilities

and someone at the end of the day has to review this code.

Now CodeRabbit's new change stack feature makes this really, really easy.

If you go to the PR overview page, you get a nice walkthrough of how the code changed, what the major changes are, and also it does some really nice things where it generates diagrams for you

that you can easily put into your code's documentation.

One of the hardest things about a growing code base is not only tech debt, but knowledge debt, right?

Making sure there's documentation that explains exactly how the code works.

Now, if you go inside the change stack, you actually see that there's layers here.

What CodeRabbit is doing is breaking down the PR into the separate layers that it affects, right?

We have the first layer, which is just the bookmark system, right?

These single couple of Go files that maintain the bookmarks.

But what's even more important is you get a very clean view here of, okay, now how does this system integrate to the overall backend API?

This gives you your semantic diff of the code base, showing you what changes and how it changes as a function of the new feature.

You know, then we have the last layer here.

100

We have the TypeScript interface

101

that shows you how the new webpage created for the bookmarks is integrated into the rest of the TypeScript system.

102

Breaking down the PR like this, guys, gives you a much better idea of exactly what the PR does.

103

You can go through and review the code, obviously, but knowing systematically how it affects the overall code base is a much cleaner path to a secure development life cycle.

104

And guys, CodeRabbit is used all over the world.

105

You can actually try CodeRabbit for free at this URL below.

106

Go try CodeRabbit out and see if your pull request needs some more work and if CodeRabbit can help you get there.

107

Thank you for sponsoring the video, CodeRabbit.

108

Let's get back to it.

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So the end result is like actually beautiful, right?

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So what you have here is a stack frame for the function in question, right?

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You have the stack frame for this function and you have this end pointer, right?

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So it's end is this and it's saying end plus equals length.

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So the pointer for end should go up and up and up the stack grows more positively down.

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That is important for you to know.

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If you don't know that, you should know that watching this channel.

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Damn it.

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But what's actually happening is we have another stack frame above us, and every time we exploit this vulnerability with these sections that have bad names, that don't have a slash in them,

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we're actually subtracting the end pointer back and back and back, 11 bytes at a time,

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until eventually the end pointer points to the return address of the previous stack frame.

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And I know you're thinking, if you're like a binary exploiter person, and you're like, wait, if this is its own stack frame here, isn't there nothing above it?

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Well, no, the actual, the contents of this buffer lives in another stack frame below it.

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So just trust me, this is how it works.

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So N goes up, up, up.

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And then using a new malformed section name that does have a slash,

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we can write arbitrary data we want to the program counter and get it to return to whatever address we want.

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Again, if this is, you know, 32-bit, like ARM, we're going to have like A, A, A, B, right?

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And if you're new to the world of exploitation, right, what's happening here, by overriding the program counter value,

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we now have the ability to arbitrarily run or at least point the CPU to a place to run other code, right?

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Like we could have put code in like another part of the image

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and we can like wrap around to like mProtect or whatever, like set the page table entry to make it executable.

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We do a bunch of evil stuff, right?

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The end goal here is

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that we're able to run code in the context of a bootloader that is doing signature verification without a valid signature.

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We are exploiting the code that is doing signature verification, and this could invalidate an entire secure boot-like process.

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I want to highlight that this in and of itself is not secure boot.

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This image would have to be signed by a secure boot key, like the manufacturer key that the actual motherboard has.

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But that being said, right, it's a really interesting primitive in the world of U-Boot, of bootloader vulnerabilities.

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Not going to dive super deep into a ton of these, but you have another bunch of vulnerabilities, like, you know, the same kind of bug, denial of service in U-Boot using an FIT image signature because of an unchecked size value.

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There are other parts of the code that use a name pointer where that name pointer can be null pointer.

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And because of that, it's going to do a bunch of other stuff.

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There's a whole bunch of interesting bugs on this write-up.

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I'll put it in the description below.

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But it's an interesting case study in the world of U-Boot, of bootloader vulnerabilities.

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And the question for the class, the question that everyone probably wants to know the answer to, would Rust have fixed this?

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Sort of.

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So again, U-Boot, the whole point of this is to have the CPU be brought up, the CPU runs a bootloader, the bootloader then enables the OS, right?

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We are at the super, super low level, name of the channel, by the way, in the boot process, okay?

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Now, doing this in Rust is actually like there are these things called peripheral access crates

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or these things called hardware abstraction layer crates

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that allow you to write code that is not unsafe for the board in question.

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That being said, doing things like raw MMIO

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that maybe there isn't a peripheral extraction crate written for is very hard to do.

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And it always does depend on unsafe code, even inside of the peripheral abstraction crates or access crates.

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There is there has to be by the nature of how embedded software works, right?

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It's global mutability, which is what Rust is designed to get rid of.

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Inside of even this code, there has to be a piece of unsafe code, unfortunately.

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But that being said, it's possible, just not easy.

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And yes, Rust would have fixed bugs like this, right?

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You would, well, actually, kind of think about it.

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I don't think you're able to fix this bug

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because all you're doing here is writing out to a pointer and a value, right?

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And then from there, it's causing the underflow.

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So I'm not necessarily sure if that's the case.

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You can't raw pointers in rust

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so there you go that's that's the answer actually you know the rust um error

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and not error the the okay and error type the result type would fix this

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because what this is actually the classical issue in c where

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you're using the error code in the error state as the

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actual value slot right this is like the entire problem

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that the rust t e or rust result type fixes

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and before we leave by the way in the code here what we're showing you

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so what i did here is i i wrote um i compiled uboot the vulnerable version

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which there is no patch for by the way yet.

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I compiled UBoot to run in QMU.

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QMU is like a system emulator, emulates an arm chip.

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And then I ran UBoot and I tried to signature validate with the FIT image that has the vulnerable structures in it.

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And then by using this, I was able to take control of the registers that are put on the stack, right?

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So R10, the frame pointer, and ultimately PC, where PC is the return address that we're going to execute next, right?

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And by doing that, this proves

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that I have at least the the ability to point the CPU to other places in the code

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that I want to run my evil stuff right now.

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Obviously, the question of like NX and ASLR comes up, but that is a different question for a different video.

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Anyway, thank you for watching, guys.

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I appreciate it.

185

If you like this stuff, check out my other stuff, and then give me a little kiss on the cheek.

186

Okay, we'll see you later.

187

Goodbye.

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Vocabulaire et conseils d’expression pour cette leçon

Cette vidéo contient 187 phrases et 2645 mots à répéter en shadowing. La partie parlée dure 12:14. Le locuteur parle vite, environ 216 mots par minute : attendez-vous à des liaisons et à des sons réduits. 82 % des mots font partie des 3 000 mots les plus courants en anglais ; le reste mérite d’être vu avant de commencer.

Vocabulaire clé de cette vidéo

15 mots de la vidéo à retenir, avec leur prononciation et leur sens :

Mot	Prononciation	Sens
boot nom	/but/	botte, bottine
vulnerability nom	/ˌvʌln(ə)ɹəˈbɪlɪti/	vulnérabilité
pointer nom	/ˈpɔɪn.təɹ/	aiguille
signature nom	/ˈsɪɡ.nə.t͡ʃə/	signature
stack nom	/stæk/	pile
rust nom	/ɹʌst/	rouille
verification nom	/ˌvɛ.ɹə.fɪˈkeɪ.ʃən/	vérification
layer nom	/ˈleɪ̯ɚ/	couche
manufacturer nom	/ˌmænjʊˈfæktʃəɹə/	fabricant, fabricante
exploit nom	/ˈɛksplɔɪt/	exploit
format nom	/ˈfɔːɹ.mæt/	format
generate verbe	/ˈd͡ʒɛn.ə.ɹeɪt/	générer
bug nom	/bʌɡ/	punaise
lend verbe	/ˈlɛnd/	prêter
verify verbe	/ˈvɛɹɪfaɪ/	vérifier

Les verbes à particule que vous entendrez

Mot	Sens
break down verbe	tomber en panne
bring up verbe	élever
check out verbe	mater, regarder
come up verbe	se montrer, sortir du bois
go through verbe	traverser
go up verbe	monter, s'élever

Prononciation à surveiller

Le locuteur utilise 39 contractions et formes réduites, comme we're, you're, don't. Prononcez-les sous leur forme courte, telles que vous les entendez.

Les sons « th »: thread /ˈθɹɛd/, algorithm /ˈælɡəɹɪðm̩/, motherboard /ˈmʌðɚˌbɔɹd/, walkthrough /ˈwɔːk.θɹuː/
Les sons « sh » et « zh »: verification /ˌvɛ.ɹə.fɪˈkeɪ.ʃən/, documentation /ˌdɑkjəmɛnˈteɪʃən/, exploitation /ˌɛksplɔɪˈteɪʃn̩/, extraction /ɪkˈstɹækʃən/, encryption /ɪnˈkɹɪpʃən/
Mots longs — placez bien l’accent: vulnerability /ˌvʌln(ə)ɹəˈbɪlɪti/, verification /ˌvɛ.ɹə.fɪˈkeɪ.ʃən/, manufacturer /ˌmænjʊˈfæktʃəɹə/, peripheral /pəˈɹɪf(ə)ɹ(ə)l/, documentation /ˌdɑkjəmɛnˈteɪʃən/

Comment s’entraîner avec cette vidéo

Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
Commencez à la vitesse 0,75×, répétez phrase par phrase, puis revenez à la vitesse normale quand cela devient facile.
Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme boot, vulnerability, pointer.

La grammaire de cette vidéo

Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :

Structure	Dans la vidéo
Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait	was found · is not meant · is allowed
Propositions relatives who / which + proposition — une précision sur une personne ou une chose	getName, which is · structure, which is · layer, which is
Present perfect have/has + participe passé — une action passée qui compte encore maintenant	I've done · have fixed

Qu'est-ce que la technique du Shadowing ?

Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.

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Pratique du Shadowing: Watch this before you boot up another device - Apprendre l'anglais à l'oral avec la vidéo

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