Dropbox Is Probably Not Stealing Your Files

https://one.darrenpmeyer.com/blog/dropbox-is-problably-not-stealing-all-your-files.html

by talon88 • 11 years ago

140 96 11 years ago

one.darrenpmeyer.com

Pure speculation follows.

I wonder if they could be calculating hashes of files and sending them off? That would be useful for automated exfiltration and targeting.

For example:

    1. Calculate the SHA-256 hashes for files in places of interest.
    2. Report the hashes upstream.
    3. Hey, this file matches one that the FBI/NSA is looking for via NSL.
    4. Download more stuff. Also identify the person and their location.
    5. Send agents/drones after them.

This is unlikely, but still in the realm of possibility. It's also untestable without more information. (Packet captures from the DLP device would be far more helpful in determining if anything of the sort is happening.)

unwind• 11 years ago

Why would a TLA look for a file with a known (hashable) content? Is that common? Is that to be seen as looking for "contraband", i.e. if you have a certain file, for instance some known part of a rookit, you might be an evil attacking hacker? I don't quite follow.

Also, the typo "Drobpox" was fun, that's a good alias when feeling suspicious. :)

patcon• 11 years ago

Tracking spread of leaked documents?

ikeboy• 11 years ago

To calculate the hash, it needs to read the whole file, which this post claims it isn't doing.

sarciszewski6• 11 years ago

I appear to have overlooked this detail. Good catch! :)

aselzer• 11 years ago

Did the author actually verify this with strace (or the mac/windows equivalent)?

It sounds like he guessed this based on I/O activity of the process. It could be enough to hash the beginning of the files, and compare the rest if a match is found in the database.

yc10102• 11 years ago

Not really, one could get a unique enough hash by reading the first lets say 10,000 bytes of each file, and it would be faster than hashing the whole file

edit: here i was bored enough > http://pastebin.com/NJEvnG1d

microtonal• 11 years ago

Hey, this file matches one that the FBI/NSA is looking for via NSL.

Or why not more mundane: another user shares a file with you. Dropbox knows that you already have the same file somewhere on your filesystem outside the Dropbox folder (or a partial match). It doesn't have to transfer that data to you.

But I agree with those saying it's probably a result of some implementation issue (Finder extension or working around some shortcoming in monitoring just the Dropbox directory).

jjarmoc• 11 years ago

This is pretty close to how their deduplication used to work, and isn't too different than how rsync works.

Of course, this gave rise to the ability to transfer files (even non-public files) quickly between Dropbox accounts provided knowledge of the hashes of its chunks, and Dropbox has since changed their deduplication. See https://github.com/driverdan/dropship

charonn0• 11 years ago

Wouldn't they need to have the file already if they know its hash?

sarciszewski6• 11 years ago

"Hey Dropbox, go find everyone who has a copy of a file with this SHA-256 hash, it's for national security purposes. Thanks"

tptacek• 11 years ago

This is a fine post, but all I can think about this situation is "or, you could just reverse the Dropbox client and find out for sure".

Speculation about Dropbox stealing files seems premised on the idea that you can't know what the client is doing. But that's not even close to true. People reverse much, much harder targets than Dropbox for fun. If any version of Dropbox published to its user base ever did anything like this, we'll all know soon enough.

sarciszewski6• 11 years ago

I would be very surprised if a workplace name like Dropbox has never been reverse engineered by a bored hacker on a lazy weekend.

Surprised and disappointed.

geographomics2• 11 years ago

I reversed it back when it was version 1.1.something, it was basically all compiled Python modules with custom encrypted code objects and non-standard opcode mappings for the bytecode.

Quite interesting to see how it worked, and useful to get the key for the encrypted logs, to see it what it actually did while running. Back then you could intercept the https connections as well as they hadn't pinned the certificates yet, to get an even fuller picture.

There was nothing obviously nefarious going on back then, but that was quite a few years ago of course.

shanemhansen• 11 years ago

I used gdb to talk the Dropbox client into opening a repl.

For examples see pyrasite, code.interact, etc.

If you specifically want to know what files Dropbox reads there are easy ways to observe this, like strace.

rawnlq• 11 years ago

Previous (successful) attempts at reverse engineering: https://www.usenix.org/conference/woot13/workshop-program/pr...

_razvan• 11 years ago

What happens here is that Windows Explorer asks Dropbox whether it should display a green or blue icon for a file. It does this for all files, including those outside of the Dropbox folder.

Full analysis here: https://news.ycombinator.com/item?id=9139657

geographomics2• 11 years ago

I couldn't be fussed to reverse it again, so instead used Rohitab Batra's excellent API Monitor [1] to figure out what's really going on.

Firstly to address files being accessed outside of Dropbox - this is true, but literally all it does is read the file attributes: https://i.imgur.com/TADvHp1.png. Moving up the call stack and disassembling the calling function, we can see that it's part of the Python runtime: https://i.imgur.com/1TBong4.png (presumably python27_lockdown.dll is Dropbox's custom hardened copy). A bit later on it does a comparison to ".bat", which identifies it as the function win32_stat() in Modules/posixmodule.c - the ensuing behaviour of this function corresponds to QueryBasicInformation as shown on the original author's Process Monitor dump. Why the Dropbox client calls stat() on files outside of the Dropbox folder (but on the same drive) is not clear, but, as the article above also mentions, that is all it does, so no problem there.

Secondly, the original author also posted evidence of Dropbox accessing various shell folders [2] - Desktop, Documents, Music, Pictures, and so on. This is true but again it's a side effect of an innocent function call, this time SHGetFolderPathW(): https://i.imgur.com/uXN31BI.png. It's actually SHELL32.DLL that is responsible for opening the folder and querying its attributes, not the Dropbox client: https://i.imgur.com/YCyTwNe.png.

Without reversing the entire program we can't say for sure that Dropbox isn't siphoning out data in some other sneakier way, but the accusations of data theft from these file events are simply not true.

[1] https://www.rohitab.com/apimonitor

[2] https://pbs.twimg.com/media/B_Kv4i3U8AEZLLt.png:large

tux3• 11 years ago

Those were my exact thoughts.

Even without having to go open IDA, I'm sure windows has enough system monitoring tools that you should be able to tell what Dropbox actually reads outside of its own data, if anything.

rlx0x• 11 years ago

You upload your files to dropbox servers, how in the world can you come to the delusion that you would notice when they accessed/searched/data mined your files?!

3JPLW• 11 years ago

(The article is about uploading files outside your dropbox folder)

radiospiel3• 11 years ago

Well, dropbox could just listen for fs events inside the DropBox folder; and it should, from a performance perspective as well as from a privacy point of view. And then "sends a few 100 kByte"? I hope this is a typo; if not, I would like to know what these are. (also: the OP's largish file (1MB) could easily fit into "a few 100kByte" after compression)

neohaven• 11 years ago

Actually, it cannot for the shell extension for the checkboxes over synced files. It needs to look at every file seen with Explorer to do that.

radiospiel3• 11 years ago

Really? The shell extension could just ask the dropbox daemon if something is known about file x/y/z, and the daemon would answer "no" if the file is outside its folder. No need to look into the file for that. Or did I miss something?

sigil• 11 years ago

Well, dropbox could just listen for fs events inside the DropBox folder...

On Linux at least [1], this is exactly what the Dropbox client does. It only registers inotify watchers on the $HOME/Dropbox directory and subdirectories. To verify:

    strace -f -e trace=inotify_add_watch dropboxd

You could also strace open/stat/read/write syscalls to verify that, aside from shared libraries and the like, the Dropbox Linux client doesn't access files outside of your Dropbox directory.

Other OSes have different file monitoring capabilities though. Anyone up on file monitoring on Windows / OS X? Is directory-specific monitoring possible?

[1] https://www.dropbox.com/install?os=lnx

radiospiel3• 11 years ago

Other OSes have different file monitoring capabilities though. Anyone up on file monitoring on Windows / OS X? Is directory-specific monitoring possible?

yes

0942v86532• 11 years ago

OS X definitely does, it's quite simple and reliable.

lucozade2• 11 years ago

Surely tradition requires that the title of this piece be "Is Dropbox stealing your files?". I mean, it's a complete waste of a Betteridge event.

DangerousPie• 11 years ago

Ha, I always wondered if there was a name for this (but obviously also never bothered to Google).

Betteridge's law of headlines is an adage that states: "Any headline which ends in a question mark can be answered by the word no." It is named after Ian Betteridge, a British technology journalist

quarterto• 11 years ago

It's in response to an earlier-submitted article: https://news.ycombinator.com/item?id=9136546

lucozade2• 11 years ago

That is, in fact, titled in the correct manner. Maybe Betteridge doesn't count if the thrust of the article is actually to point out that "no" is the correct answer. I hadn't thought of that.

whizzkid• 11 years ago

" 1 - Create a large-ish file (1MB) outside of the Dropbox folder

2 - Monitor the network usage of the Dropbox application to see if it sends enough data that it could be that file

I can not really say if Dropbox steals them or not. But if i were a Dropbox engineer and want to know about those newly created files, i wouldn't want to send the whole file to server at all.

- Send file name with its extension

- Send file size

Compare these to dropbox's blacklist file (imagination only) in another server. If there are any matches, mark user as "whateveryouwant"

As long as there is a network activity when a new file created, it is and will always be suspicious to its users.

ProAm• 11 years ago

And they don't have to steal the whole file at once, why not chunk it out and do bits at a time over a few days. This is tinfoil hat territory, but they'd still get the file and network traffic wouldnt be overly suspicious.

jamiesonbecker2• 11 years ago

You don't need to retrieve the file if you already have it.

pwnna• 11 years ago

Speaking of which, does anyone run apps like this with a different user than their own?

I'm thinking of something like

    /home/dropbox drwxrwx--- dropbox <youruser>

lutusp• 11 years ago

Quote:

"A simple protocol can give us an idea of whether data is being sent to Dropbox:

1. Create a large-ish file (1MB) outside of the Dropbox folder

2. Monitor the network usage of the Dropbox application to see if it sends enough data that it could be that file

3. Repeat with many different files, etc.

Doing exactly that, Dropbox only sent a few hundred KB after “accessing” the target file. Seems unlikely that Dropbox is uploading files outside your Dropbox folder."

This test approach has a problem. A more realistic test would be to place a well-compressed file, one that by definition cannot be made smaller, on Dropbox and see what the system traffic size is for that file. For an optimally compressed file, if the system is reading the entire file, the read size will more or less equal the file size.

Retric• 11 years ago

You’re still missing the possibility of DB uploading a hash vs standard file compression. Even if they never upload the full file plenty of people would love to know if any of your files was on some list. (Classified information, piracy, etc.)

darrenpmeyer• 11 years ago

If you read the discussion near the end about why a few hundred KBs, you'll see that the first test file I used was a JPEG embedded in a Word doc (the latter because the original claim used Word files), which should be very difficult to compress.

To be fair, I added this section after several people pointed this out, so you may not have seen it.

lalos• 11 years ago

Any thoughts on SafeMonk, which they claim end to end encryption and piggyback on dropbox?

jostmey• 11 years ago

Dropbox has too much to lose and not enough to gain by stealing your files. The accusation borders on paranoia. That said, Dropbox is a closed system, and I always trust open systems more.

rayiner• 11 years ago

As an aside, I've been using Sparkleshare (built on GIT and SSH) lately. It's pretty good, and sucks up less battery on my MBP than the Dropbox client (maybe because it's not watching every file in the system!) And not only is it open source, but you can see a log of all the git commands and fix things manually if necessary.

My only lament is that it doesn't work that well over the intermittent connections. It'd be neat to have something robust like mosh (https://mosh.mit.edu) for file sync.

mbq• 11 years ago

There is also unison; it is not automatic (custom inotify script is required to mimic Dropbox, and it will force manual intervention upon conflicts) nor stores history, but handles large blobs, many clients and crappy connections quite well.

copsarebastards4• 11 years ago

The cycle of security is this:

1. Security experts see a security hole and note that it could only be used by a widely trusted company or government.

2. People note that it's also possible that it's not happening, and claim that the widely trusted company or government would never use the security hole.

3. It is discovered that the widely trusted company or government has been using the security hole.

Dylan168073• 11 years ago

"Touches files it doesn't have to" is not a security hole.

copsarebastards4• 11 years ago

"Users install program that touches files the users might not want it to" is a security hole. The unknown is whether Dropbox comes with malware which takes advantage of that security hole.

jamiesonbecker2• 11 years ago

Perhaps it's semantics, but you're right - it's not a security hole.

It's worse.

Exceeding authorization is exploiting an existing hole.

chinathrow• 11 years ago

"This is, by necessity, a system-wide process."

This is, by design, a fucking huge defect of the underlying system calls.

Give the OS a list of folders to watch. Dropbox should not even get a callback for a file it's not is supposed to watch.

raverbashing• 11 years ago

See: inotify in Linux

krakensden• 11 years ago

inotify is by far the best of the filesystem notification APIs. It's wildly reasonable.

kevingadd• 11 years ago

You can constrain filesystem callbacks on Windows, I have no idea why Dropbox doesn't.

r00fus• 11 years ago

Exactly - how much information can be inferred from the file and path alone - in a lot of my cases (for very personal files), quite a lot.

If Dropbox gets to interpose itself in every file update systemwide, that sounds like it's getting too much of my information. Encrypted/Stego drives don't matter - once you open it up to the system, Dropbox sees when you touch it.

All I can gather from this discussion is that I'm glad I'm not using Windows and Dropbox together.

Someone1234• 11 years ago

This article makes me irrationally annoyed by how lazy the author was. I was able to produce a test in under 5 minutes that disproves the article's core assumption:

The Dropbox application uses a filesystem monitor to detect when changes are made by monitoring filesystem write events. This is, by necessity, a system-wide process. So DLP alerting that Dropbox is “acccessing” a new file shouldn’t be surprising.

THAT IS NOT HOW THAT WORKS!

Sorry, I am calm now. As someone who has spent quite a lot of time using Windows' File System Watcher functionality, I know that that is nonsense. Windows monitoring/watching is conducted at the kernel, when an IO operation occurs that hits a registered monitor it fires off an event (windows message) to that process to let it know, the process itself never accesses that file directly.

But just test it for yourself.

1) Download Process Monitor [0]

2) Start Process Monitor, turn off Registry, Network, Profiling, and Process events.

3) Set the include (included processes to monitor) to [whatever executable you build]

4) Build this (see examples section) [1] in C#/VB.net and run it

5) Set the process name in #4 in the include in #3

6) Write to a file in C:\ (that's the default in the example program/source)

7) You should see some Console.WriteLine() output indicating the file watcher is working. If not run as administrator.

8) There you go. As you can see, no direct file accesses to the file. The monitor events are fired as you can see, but the file remains untouched directly by your program.

The author could have done this. Why didn't they? It isn't like I had to even write one line of code or have some kind of specialist knowledge of low level kernel functionality...

PS - I don't know/care if DropBox is stealing your stuff. I just wish the article's author had at least fact-checked before they claimed that "that is how this works!!!" when in reality that is untrue. That is how it works for Anti-Virus because AV scans within files to see contents, it isn't how it works for most processes which just use the file watcher functionality. If DropBox chooses to look inside files, then why? There is no need for that.

PPS - If DropBox do have a system wide file watcher, that is just lazy. It will reduce system performance, and they could have just as easily set it up to point just to folders DropBox is configured to watch.

[0] https://technet.microsoft.com/en-us/sysinternals/bb896645

[1] https://msdn.microsoft.com/en-us/library/system.io.filesyste...

chisleu5• 11 years ago

Read their TOS and compare it to Google Drive's TOS.

The insane rights the Google TOS grants to Google are why it costs ~ 1/2 as much.

It is also an indicator that Dropbox is less shady. They don't grant themselves rights to do anything with your data outside of the normal things you need them to do to offer the dropbox service for your use.

Unlike Google, which could for instance, use your personal photos of your kid eating ice cream to try to sell you ice cream via road side LED billboards.

eli• 11 years ago

I think you're misunderstanding the TOS. I do not think Google is subsidizing their storage costs by abusing your private photos.

shdon2• 11 years ago

They might not be doing it (and probably aren't), but they do have the right.

chisleu5• 11 years ago

I think you aren't actually reading it. I do not think Dropbox is less good at running storage than Google or Amazon, yet Google is 1/2 the cost.

Raphmedia2• 11 years ago

We all know that the reason Google is running face recognition and photo recognition software on your all your files is to cross reference it with databases of paedophilia and terrorism !

Raphmedia2• 11 years ago

Why the downvotes?

http://www.telegraph.co.uk/technology/news/11012008/Paedophi...

ubernostrum• 11 years ago

I'm aware of nothing in Google's terms which isn't in the terms of every other user-generated-content service that has lawyers on staff.

In order to make copies (distributed storage, network traffic, etc.) and show copies to people -- including you, or anyone you choose to share a file or post with -- they basically have to have a license from you, or they're potentially on the wrong side of copyright law.

chisleu5• 11 years ago

Then you need to read the damned TOS side by side with dropbox. They are significantly different in scope and the rights allowed.

shawnhermans• 11 years ago

You claim that Google could use personal photos of my kid eating ice cream to sell advertising? This seems directly against their terms of service found at http://www.google.com/policies/terms/.

Some of our Services allow you to upload, submit, store, send or receive content. You retain ownership of any intellectual property rights that you hold in that content. In short, what belongs to you stays yours.

Do you have any proof of this ever happening? Do you have any legal case that support your claim? Can you please point to the text in their TOS that leads you to believe this?

chisleu5• 11 years ago

You need to actually read the TOS for dropbox. It says they can use your stuff for any service they offer now or in the future.

I don't need proof. You need to go read the TOS I mentioned already.

bebbiwebbi• 11 years ago

"The Dropbox application uses a filesystem monitor to detect when changes are made by monitoring filesystem write events. This is, by necessity, a system-wide process. So DLP alerting that Dropbox is “acccessing” a new file shouldn’t be surprising."

I think this SHOULD be surprising to any competent software engineers. That isn't how the file system watcher works.

meira• 11 years ago

Dropbox Is Probably Ready To Do So As They Want

venomsnake• 11 years ago

If dropbox get to send metadata about files outside of the folder could be damning enough.

Hey you have in your downloads folder 3 new files per day whose file names hints they were send by FB user X. I could make an educated guess about their content.

MrDosu4• 11 years ago

About every form of backup software will use change journals to identify what to backup and how it changed.

Change journals are streams that are per volume (so to monitor some directory in C:\ i have to monitor the C:\ change stream).

It's just how NTFS works. It's shocking that this was allowed to reach this kind of publicity because it's just a guy attaching a diagnostic tool to a system where he doesn't know whats happening and then proceeds to freak.

Software like this will have plenty of file access for metadata, not only on the backed up files.

TheLoneWolfling3• 11 years ago

And this is where having the API actually support, say, monitoring only items in a single directory would be good.

MrDosu4• 11 years ago

Well there is, but it's unreliable in certain edge cases. At least not reliable enough for a backup solution.

xer• 11 years ago

It's very unlikely that dropbox would upload every changed file from your computer, that would not go unnoticed.

A desirable capability would be on-demand upload or download of any file on the clients system. For that you would need the entire filetree+checksums so, imo, that's what it's syncing.

jamwt• 11 years ago

Uhh... no, no we are not. s/probably //

Animats• 11 years ago

The original article is titled "Dropbox Is Probably Not Stealing All Your Files". From bandwidth consumption, you can tell it's not stealing all of them. Whether it does so selectively, on command from the mothership, is another matter.

vacri• 11 years ago

Separate from the privacy concerns, what about network traffic? "a few hundred kilobytes" for every file you create adds up.

darkhorn• 11 years ago

If you are an ordinary guy then even if Dropbox steals a file it won't matter much. If you are a government, Airbus, Snowden, Aselsan, or Comodo you should not install Dropbox even if you trust Dropbox.

anonbanker• 11 years ago

I stooped trusting dropbox when condoleeza rice got added to the board.

deciplex• 11 years ago

Reminder that Dropbox was mentioned, by name, in NSA documents released two years ago as the next target they intended to subvert. Also reminder that not long after that they named Condoleeza Rice, celebrated apologist for warrantless wiretapping during the Bush administration, to their board of directors.

Yes, it's possible they named her to their board in good faith, and it's possible they also resisted the NSA somehow, where Google and Microsoft and Yahoo and countless others failed. But, do you consider it likely enough to bet your privacy on it? It seems to me you would be foolish to do so.

The only other excuse for it I can think of is that it's so obviously corrupt that it proves they aren't corrupt after all - that no one could be that stupid. I reject such meta-reasoning. They are simply corrupt.

jinushaun• 11 years ago

The tin foil hat is strong with this thread. People should read up on Windows Explorer shell extensions before making comments. It's like saying regexing email addresses to check for valid input is the same as stealing emails addresses.

Dropbox Is Probably Not Stealing Your Files

Related Stories