Websites have a new way to spy on visitors: analyzing their SSD activity

Browsers have an absolute insane level of relatively unchecked permissions to do whatever they want on a client.

There's a lot of effort by browser developers to scope creep the browser into essentially being an OS-agnostic tech stack (one where, conveniently, code can be shipped across the network "as necessary", removing a lot of user agency for the software being ran); Chrome being the biggest driver of this, while Firefox has an extremely weak spine in trying to limit it.

It's fairly dire and I wouldn't be surprised if there's a lot more of these side channel attacks in a lot of web APIs.

My shortcut for launching "clean" Chromium session is `chromium --user-data-dir=$(mktemp -d)` -- each launch creates a new transient profile directory under /tmp, which is itself a RAM disk. Persistent settings are achieved by setting system-wide defaults in /etc/chromium, including using system-wide managed policy JSON.

Is this surprising? Websites have long been silently writing to disk, for cache, cookies, and blobs. OPFS just provides a file-system-like API for ultimately the same functionality

That surprised me as well.

I thought the whole point of cookies, local storage, session storage, and indexed DB were to avoid what origin private file system is doing.

You mean I could have just saved stuff as a file this whole time instead of serializing it to a string? Why didn't we just do this from the start?

Hostile LLMs? In my browser? At this time of the year?

> Wait, wait, wait: browsers allow websites to store junk on my drive?

Technically even a cookie is junk on your drive

> Without even asking whether the site can use local storage?

Would it be practical to ask permission for every site you visit? It would be better to periodically check the size of your home folder (where the browser profiles normally reside)

The funny part is that "put your browser profile on a ramdisk" used to sound like an obsessive performance tweak, and now it starts to look like a privacy mitigation

If you open an incognito window in chromium it is profile on ram

> Without even asking whether the site can use local storage?

Where did you see this in the article? I had some recollection that Firefox at least did require asking the user.

And Web Developers want more and more OS features built into the browser. This is why I'm against it. Features are only ever abused.

Sic transit gloria mundi :'(

It depends what you mean by "general purpose." First, these things generalize more often than you'd expect. Second, even in the absence of generalization they're still useful for, e.g., fingerprinting activities to manufacture a unique ID where non previously existed.

Publish or perish. It worked once, in a controlled lab, mostly (80-90% guess). Good enough for more millions in funding..

Not really joking here.

https://hannesweissteiner.com/

https://hannesweissteiner.com/publications/frost/

That's basically just a research, theoretical attack vector. It doesn't mean it's viable for general purpose old school mass privacy invasion

> Simply add random access times.

That doesn't work. Because the random times are uniformly distributed it's possible to remove it from the data by additional sampling. You do make it harder because you need a lot more data, but it's still possible to extract the signal, because the noise is uniform.

The paper (https://hannesweissteiner.com/pdfs/frost.pdf) cites two earlier papers (from 2014 and 2017) that did the same for HDDs.

I got $HOME in a huge HDD because it was cheaper. I guess we belong to the cool kids club now?

Or mine where the entire browser profile is on a ramdisk.

Higher IO latencies in HDs might actually make this attack easier - more contention means more bits of data.

I laugh at your spying attempts from my cURL e-mail service that I use instead of a web browser.

I assume it's something like this:

Attacking website periodically makes random reads from a large file in localStorage. Other tabs and websites open have Javascript running that periodically performs operations that will result in SSD traffic. For example, GMail has a certain polling interval to check for new mail, and each request is going to result in a cache write that makes the SSD busy and delays other conflicting IO operations. Reddit checks for new chat messages. Large memory-heavy websites get paged out of RAM.

The pattern of IO operations that a website makes creates a fingerprint of interference with the IO ops that the attacking website is doing, showing up as differing amounts of latency as the SSD is periodically busy. This fingerprint can then be reconstructed to a specific website by training a CNN on it, basically using a neural net to classify a certain pattern of delays to the IO ops that other websites are doing.

In theory it makes sense, but it seems very noisy. Anything that makes absolutely zero requests or IO operations in the background (like say HN, or most old-school text sites) wouldn't show up, and would be indistinguishable from any other zero-request site. And having other sources of IOps on the same computer - say you're running an Ethereum client that's perpetually updating the blockchain, or you're downloading a bunch of torrents, or you've got DropBox and it's syncing your directory - would introduce noise that throws off the classifier.

That’s timing the cache, that’s old stuff by know. As I understand, this writes a relatively large file („Gigabytes“) using this OPFS api, which is different from the „localStorage“ api. This seems to use actual filesystem storage on the client, instead of living completely in memory (which may be reasonable given the size of files supported). This allows to actually time SSD IOPS latency by doing random reads.

Collected enough of these samples, together with the information of what else runs on the host, put that in the ML-Blender and the result will be able to tell you, with some accuracy, from a given set of samples, what’s running on the host.

I am sure i misunderstood some things because there are so many caches and unknowns in that setup that I struggle to understand how there could be any correlation, but that’s my understanding so far.

There's no such thing as a sandbox "on your machine" when you really think about it. The code still runs on the same hardware and there are tons of ways to fiddle with said hardware that could be exploited (like rowhammer). The only "real" sandbox is fully dedicated hardware down to bare metal with zero connections to sensitive systems.

And now that Google's web environment integrity is getting repackaged into captchas, it seems we won't even be able to try to block such things in the future...

Been doing that for years and do not regret it.