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Comment by madez | Hacker News Reader

Recently here on Hacker News I had a short discussion with Steve Klabnik about JavaScript and WebAssembly among other things.[0] My point is that to execute randomly downloaded code is realistically impossible to secure, practically used to deliver malware and usually used against the interests of the user of the computer. If I can infer from Steve's stance the opinion of Mozilla, then it's sad to see that the only big browser developer organization I had hopes in simply waves these problems away and keeps on making JavaScript and WebAssembly more usable and widespread. It's disheartening to see that.

The connection to this talk is that they demo triggering a backdoor hidden in microcode by executing some WebAssembly code in an up-to-date FireFox.

[0] https://news.ycombinator.com/item?id=15981178

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Author here: I chose WebAssembly, because it allowed for easy insertion of an instruction we understand perfectly and can backdoor. With more work we could have highjacked an instruction in the actual binary of Firefox and started the attack from there. WebAssembly simply gives primitives that allow for an easier attack (emitting of a specific instruction, chosing constants and predictive code generation). Not WebAssembly itself enabled the attack, it just made it easier.

Exploiting HTML or font rendering is more work, but as you still run known instructions in a known sequence processing known data the primitives are still there. The same can happen for anything that processes foreign data, be it script, video, images or just CSV.

Let me first thank you for the incredibly important work of finding and documenting behaviour of hardware we use.

I see your point. However, if it's harder for the attacker, it is already a win. Also, this is just one example where JavaScript/WebAssembly are used to deliver/activate malware. There are many other examples.

Besides that, even if JavaScript/WebAssembly implementations were provably secure (which they aren't), I would be against them for the other reasons I described in other comments here.

Sorry if this is a dead point that’s already been discussed but: if the code is sandboxed then what is the difference between arbitrary WebAssembly and arbitrary JavaScript other than speed? It all comes down to instructions executing in the same sandbox doesn’t it? From a security perspective what does this actually change? Is it just that there’s a greater capacity for obfuscation?

From my experiences of reversing Windows x86 applications, I don't think WebAssembly has a greater capacity for obfuscation. In fact, I think WebAssembly is less capable of obfuscating code than JavaScript.

It is because WASM does not allow self-modifying code, which is a highly effective obfuscation technique as it can hinder static analysis. On the other hand, JavaScript has eval among other things that can be used to dynamically craft and execute code during execution. I've never seen such JavaScript but it would be quite cumbersome to trace code within a call to eval within a call to eval, and so on. You might need to build a custom V8 to record strings passed to eval when reversing such code.

It makes the use-case for this type of code deployment wider, it's more effective at what it's already used for, and it's also less auditable.

These are three reasons why developing and supporting WebAssembly is finally against the interest of the users.

The harder, less efficient and cumbersome this type of drive-by code deployment is, the less attractive and used it'll be.

Also, sandboxing helps only until it doesn't. It's a futile task, especially when we don't have complete control of the hardware, which we don't, because the chip developers don't tell us complete specificiations and functionality.

Hi. I write sandboxes for a living.

> Also, sandboxing helps only until it doesn't. It's a futile task,

It really isn't futile. How many major security holes in Chrome's sandbox have actually done serious damage? Yes, they happen from time to time, but not that often, and they are automatically patched shortly after (or before) disclosure, making them really uninteresting for attackers to try to exploit.

Realistically, the biggest security threat to real users is phishing or similar deception. Many users can be fooled by a page that looks like an error from their operating system telling them that their computer has a virus and they should download a tool to fix it. You don't need JavaScript for that.

Realistically, the highest-impact non-user-error security problems are logic flaws in complicated server code that never intended to run attacker-supplied code in the first place. Think SQL injection, confused deputies, missing access control checks, buffer overruns, SMB (Windows file sharing) bugs exploited by worms, etc.

Ironically, modern JavaScript sandboxing is so good -- with so much careful scrutiny by really smart security researchers -- that realistically it's not remotely the easiest target on your system these days. The easy targets are the software that isn't written with security in mind, and the users themselves (phishing).

> especially when we don't have complete control of the hardware, which we don't, because the chip developers don't tell us complete specificiations and functionality.

JavaScript and WebAssembly don't have direct access to hardware. WebAssembly is not assembly, it's a platform-neutral bytecode that gets recompiled for the host after download.

Although I take your points, I disagree that JavaScript is more auditable as-is. In either case I will need tools to unwind/flatten/de-obfuscate the code and audit it. I believe it would take me about the same amount of time in either case, depending on the scope of the audit.

Regardless, it’s a trade off. Although I agree we should have a web that doesn’t need JavaScript to function - I believe that is a separate argument - I think in this case, while we already have it, I’ll take WebAssembly for the speed and new applications it helps support.

I certainly wouldn’t want to see “Web Assembly” blobs in my browser that I’m not allowed to inspect, which again is another argument, IMO.

> [...] My point is that to execute randomly downloaded code is realistically impossible to secure, practically used to deliver malware and usually used against the interests of the user of the computer. [...]

This argument has been rehashed over and over again. Some of the mass appeal of the web, as a platform, is that random arbitrary code can be downloaded and run inside a sandbox. It appears that these web technologies will continue to be used regardless of any security implications.

If users demand something like JavaScript or WebAssembly, do you have an alternative proposal to satisfy them?

Rehashing an argument does not make it wrong, and continuing doing so is still important if it's valid and not considered accordingly.

Users don't demand JavaScript nor WebAssembly, some developers do. Users want to easily discover new programs/games/whatever. If they were presented those equally easy and convenient in another form, they wouldn't even care.

Those developers that demand JavaScript and WebAssembly have mostly interests that go against the interests of the users. The developers might want to hide parts of their code or underlying data from the user, or force presentation in a certain form (ads), or avoid the orderly way of delivering software through proven ways like distributions, possibly to achieve the former two goals.

Now, where does Mozilla stand in this conflict? I realize they don't stand where I thought they would stand.

I want the web, but without random drive-by code execution. Code must be delivered by other, more accounted for ways.

> Those developers that demand JavaScript and WebAssembly have mostly interests that go against the interests of the users.

This is stating the obvious, but...

For anything even mildly interactive, JavaScript is absolutely essential to creating a good (or even bearable) user experience. With purely static HTML, every interaction requires a page reload, which is painful. Users absolutely do want modern, low-latency UX.

Moreover, you literally cannot build things like Slack or Google Docs without JavaScript. Users want these products. HTML-only GMail is barely possible but it's really painful to use. Users want GMail with JavaScript.

Maybe you don't want these things. Maybe you are happy with pure-HTML interfaces, or doing anything interactive through dedicated native apps. But there are very few people who prefer it that way. Please don't presume to speak for all users, or accuse Mozilla of working against users, when it's your specific needs that are unusual.

HTML is capable of a dynamic interface, but it must be statically defined. With HTML5 we even have videos. The linked webpage including video work like a charm with JavaScript disabled. Furthermore I'd welcome a HTML6 as long as it stays non-programmable, and don't see why it shouldn't be able to be a low-latency interface. The interface of the linked video feels very snappy.

I agree that HTML-only GMail in the browser right now is a mess, but that's because a browser is not an e-mail client, and shouldn't be one.

People are trained for certain behaviours and often don't want to change from that. On the other hand they like new shiney software and things to try out. That explains in my eyes why for example Google Docs (seriously, office editing in the browser?!) is used. Also, Google has a good reputation for software.

I think most people are simply not aware of the dangers, downsides and alternatives of this approach. The behaviour was learned when people talking about a globally snooping NSA were called crackpots.

On top of that, Google has no business interest in offering a standalone office solution, so people either use Google Docs in their browser, or not at all. Supply creates its own demands.

How discoverability and ease of obtaining trusted code is solved, is a technical problem. I could imagine markup-only webpages which can call locally installed programs to appear in the tab, but the prorams are installed in trusted ways. That's just one spontaneous idea.

Mozilla is making it easier for people to use technical solutions that are suboptimal for them. This has a network effect and shapes the web to be a worse place. That is what I accuse Mozilla of, and I stand by it.

> HTML is capable of a dynamic interface

HTML is capable of very specific, fixed functions. Sure, video is one of them. But video is not very interactive. You press play, and then you watch. Interactivity in plain HTML is very difficult.

> People are trained for certain behaviours and often don't want to change from that. On the other hand they like new shiney software and things to try out.

No no. People don't use these products because they were "trained" for it. The world of installed native applications existed before the web. The web took off because it's actually way better for many people. Not having to manage installing apps is awesome. Being able to access your data from multiple devices trivially is awesome. Not having to worry about backups is awesome. Being able to collaborate in real time is awesome. People don't just like this stuff because it's "shiney", they like it because it's really, genuinely useful.

> I could imagine markup-only webpages which can call locally installed programs to appear in the tab, but the prorams are installed in trusted ways.

That would actually be way less secure, because those locally-installed programs are almost certainly not security reviewed to the extent that the JavaScript sandbox is. They are far more likely to have exploitable bugs than your JavaScript sandbox. It doesn't matter that you "trust" them.

In practice, the vast majority of programmers do not know how to write secure code. We can't realistically fix that. The answer is to give them programming environments where they can't get it wrong, or at least they can only hurt their own app. We accomplish that with sandboxing.

Starting and stopping a video is an interactive action. Even a drop down menu is interactive. Arbitrary interactivity may not be possible, but I think that is totally acceptable for what we are talking about: remotly delivered, unaccounted, unreviewed and directly and automatically executed code.

That the local and native programs are not as good as the browser-based abominations is no argument for that technology; there are reasons for the businesses to choose this way despite (or because) how bad it is for users.

Code that comes for example from a distribution is signed and maintained by someone I can easily identify. It is looked at by more than the author. I can track the path of the code backwards, if something nefarious happens. That justifies trust in that code.

The comparison of that code with the JavaScript sandbox is invalid, it's to be compared with the delivered JavaScript. There is no reason why even trustably delivered code shouldn't be sandboxed. The comparison of that sandbox with the JavaScript sandbox would be apt.

I agree that sandboxing is important, even for local programs.

OK, I'm glad we agree that native apps ought to be sandboxed too. Unfortunately no major desktop OS does a good job of this yet, which is why, realistically, today, choosing web apps over native apps actually makes your system more secure. Maybe that wouldn't be true in an ideal world where desktop apps were sandboxed as heavily as web apps.

But you're still in denial about the fact that web app delivery is hugely valuable to a lot of people (yes, to users). This isn't even remotely debatable. SaaS is now a $100B/yr industry and growing rapidly. People wouldn't be rapidly replacing locally-installed apps with SaaS if they didn't really want it.

You really can't just proclaim that everyone should give all that up based on your ideology about how software "should" be delivered.

I think we don't contradict each other necessarily. JavaScript applications not delivered by websites but through the package manager would be okay for me. We would have the sandbox on one side and the accounting and responsibility on the other side. After all, even the JavaScript sandbox (FireFox) itself is delivered how I think software should be delivered.

The size of the market is no argument. Supply drives demand.

I don't simply proclaim how things should be done. I point out problems, criticize the status quo based on sound facts, and point to better solutions. What else do you suggest?

> Supply drives demand.

There's no shortage of supply of desktop apps, yet web apps are gaining ground rapidly. This indicates that people prefer web apps for some reason.

> What else do you suggest?

Build it. If you truly have a solution that is better for users, then you can make a lot of money if you bring it to market. Then you not only prove you were right, but you make the world a better place and get rich in the process. :)

But somehow you're going to need to make desktop apps significantly better than they are today. You won't win by telling users that their preferences are wrong, you win by giving them something better.

With labels, hidden checkboxes/radio buttons, and some awkward CSS you can make no-javascript collapsible/expandable content, tabs, user-changable colour themes, and other horrible abuses of pure HTML+CSS. With :hover and transitions, you might even be able to make something turing-complete that runs automatically as long as the user's cursor is somewhere over the page! (last time I tried, a box that moved away from the mouse on hover, then automatically returned because it was no longer under it did not move endlessly unless there was an animation/transition on the movement. Could you have a clever way to send signals up the DOM heirarchy by altering the presence/absence of scrollbars or forcing a div to be wider, changing how elements layout with respect to cursor position?).

In those cases, it's certainly easier to use javascript, though.

Hat's off! I'm astonished that people like this still exist. I really have no idea under which rock and in which tinfoil hat they still survive. But we need more such people, so please keep your windmill-fighting.

In the meantime, before they deliver "non-programmable HTML6", they deliver HTML 5.2 (or was it .3?) with DRM inside. Mozilla? They produced buggy, resource-hungry browser for decade (was less resource-hungry than competition, now the same). What to expect from them? These Xmas time, when opening a new empty browser page, they show an ad phishing me for money. And that's exactly what everyone expects from them.

The stories about HTML with DRM and unsolicited adds from Mozilla were discussed here on HN. So again, no idea what tinfoil hat you wear, but godspeed with keeping it up.

Users don't demand JavaScript nor WebAssembly, some developers do.

Exactly. One of the biggest use-cases I see for JS/Wasm is in implementing DRM obfuscation and more insidious advertising/tracking code.

Logical sandboxing is a perfectly possible problem that can even be made correct by formal methods. Browsers don't use a proven correct implementation because testing are enough to get almost perfect already.

So, are your concerns about side channel attacks? Side channels are nothing more than undocumented (and sometimes unfixable) logical features. Opening the microcode for inspection and making it patchable will only reduce the number of undocumented features.

On a von Neumann architecture, there is no actual distinction between code and data. Every CPU architecture in widespread use is a von Neumann architecture (GPUs, it should be noted generally aren't von Neumann). What this means is that loading data from unsecure, untrusted sources is potentially the same as executing code. In practice, this is actually very often the case--a buffer overflow trivially turns data into code.

With that in mind, what realistically is possible to do, over than to declare that everything can only be read as plain text (and hope there's no exploitable bugs in font rendering of system fonts)?

There is a huge difference from the security perspective between rendering a static HTML site and executing JavaScript. That theoretically they might be close has no practical meaning, and insisting on it may paralyse us into doing nothing. Securing font rendering or HTML rendering is achievable. I suggest replacing the C code by code written in a language with stronger static verification, like Rust.

Also, JavaScript and WebAssembly (the latest starting with this talk) are actively used for unauthorized access to computers. It's not like I'm pointing out theoretical attack possibilities. This makes the matter more urgent.

What about JS is so odious? That it's Turing complete? Well, so is XSLT, yet you don't seem uptight about people implementing it.

JS does provide some very valid use-cases, and two of them that come to mind are interactivity and displaying static data that has no neat representation in HTML (e.g., Mathjax and d3.js for charting).

My point is that JS is far from the only massive, complex, potentially security-laden hole in a modern web browser. Audio/video codecs are notoriously complex, and font rendering also has this nasty habit of causing kernel crashes on Windows. These have been used for active exploits. The way you achieve security is you have to look at the risks and work out ways to mitigate them. There are ways to be quite secure even allowing JS execution.

The addition of the NX bit to CPUs blurs the line between Von Neuman and Harvard architectures.

Giving an attacker a JIT makes it easier for them to lay out memory with the NX bit set to zero (executable memory) that they can later jump into.

Return-oriented programming can still be used to hijack a program that whose executable parts are locked down at runtime, having a JIT just makes things easier.

What is "code" anyway except instructions? The Harvard-Von-Neumann distinction is really a continuum. Even today's computers draw important distinctions between data and code: for example, we have separate data and instruction caches, and Linux has special caching behavior for PROT_EXEC pages.

(The latter is an annoyance, BTW: there's no reason to treat Java bytecode, say, differently from PROT_EXEC pages. Executable protection should have nothing to do with active or inactive list membership.)

If I recall correctly, WASM separates code and data, along with a bunch of other security features.

> If I can infer from Steve's stance the opinion of Mozilla

Mozilla's decisions speak for themselves. There is no need to reference individuals, and less so without very solid basis (which there wasn't).

> My point is that to execute randomly downloaded code is realistically impossible to secure

This is absolutely not true if you have a MMU and something like a protection ring. In such an environment code by default can do nothing malicious. The only thing making it insecure in any way are the syscalls offered by the operating system.

> If I can infer from Steve's stance the opinion of Mozilla

Please take my opinions as my own.

Sorry for referencing you that way. I can't change it anymore. I could have pointed to decisions taken by Mozilla to explain my disappointment instead of extrapolating from your statements. Even if your view were exactly what I was criticizing Mozilla for (which I neither think, know nor assume), there was no need for that reference since my critique is not specific to a person. It's bad taste to point to a single person. On top of that, the inference wasn't well justified. I realize I handled that badly, and I learn from that. So, I actually thank you for pointing it out politely.

I don't mean to justify but rather to give context when I say that these discussion are not easy because there are lots of arguments and comments of varying degree of quality and emotional content, and contradicting voting. It's hard to represent an unpopular opinion. Still no justification whatsoever.

No worries! Just wanted to make it clear :)

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