Find Friends Abuse

http://blog.snapchat.com/post/72013106599/find-friends-abuse

by michaelrbock • 13 years ago

68 64 13 years ago

blog.snapchat.com

xSwag• 13 years ago

There is an easier way to solve this issue: Bug Bounty.

It worked for Google, it worked for Facebook and its working for Yahoo! Infact, it worked so well for Google that they recently increased the rewards. A venture-backed startup like Snapchat that stores private pictures (even temporarily) should have no trouble paying out $5k a few times for vulnerabities.

awhitty• 13 years ago

They were aware of the vulnerability for months. They chose not to adequately address it. A bug bounty wouldn't solve that problem.

octatone24• 13 years ago

The problem is they did not see it as a vulnerability, they touted it as a feature, and even made a blog post outlining how you could exploit it. That was the most WTF event in following this story.

pkfrank• 13 years ago

I really feel like SnapChat is fumbling this whole thing. They ignored the security warning, and now seem to be blaming the security group for the leak of info:

On Christmas Eve, that same group publicly documented our API, making it easier for individuals to abuse our service and violate our Terms of Use.

The funny thing is that folks on HN and in the tech community generally will fault SnapChat for their callous attitude to security and pitiful response. But 99.9% of their users won't know or care, and investors will consider this a "lesson learned" and move on without a second thought.

Once the 24/hr news-cycle moves past the hyperbolic "SnapChat Hacked!" headlines, this ordeal and their pathetic response will slip into the forgotten-ether of low-impact data leaks.

nkvl• 13 years ago

If only it would go away so easily. The PR strategy they have going on, if taken at face value, is a sure way to have stuff like this happen again; and every time they'll be the losers. Pissing off the same people who are trying to help you is childish at best.

superuser26• 13 years ago

callous attitude to security and pitiful response

How would you have designed this functionality in a way that isn't vulnerable to the same attack?

Rate-limiting can slow you down, but you could run the script for months if you wanted. Fundamentally Snapchat is using user-supplied data, and users can lie.

Maybe we can check if they are lying by querying a database of people who have verified that they know each other? Oh wait, that's Facebook. HN would be boycotting on principle and screaming about violation of privacy.

thirsteh• 13 years ago

Rate-limiting can slow you down, but you could run the script for months if you wanted. Fundamentally Snapchat is using user-supplied data, and users can lie.

You can make the same argument about employing exponential backoff on a login screen. It's still very effective deterrence.

joyeuse6701• 13 years ago

There aren't great simple solutions to this issue AFAIK, but here's my take since I had a similar android app feature:

Want to find friends using contacts in phone:

Snapchat solution: pass number(s), return user info if number(s) in DB. +rate limit

Problem: rate limiting is not enough in this case.

Other solution:

Save contact lists of two users. If user requests friend look up, compare contact lists.

Basically return user info if the two numbers have each other in contact list, thus a verification they know each other.

Duping the snapchat system with the old method won't work, but drawbacks are that you have to store a copy of user sensitive information, and if that gets out from your servers in some other hack, that would be really bad, as bad if not worse than the first since it has more information, i.e. who knows who. Also less efficient, space and time wise.

hrktb• 13 years ago

You seem to take position to defend the snapchat stance ... I read it as a validation that there is a tradeoff made by design, and anyone caring enough about privacy wouldn't have implemented the feature in the first place.

Privacy doesn't have to be the goal of every service, let's just admit that it not a main concern of Snapchat either.

Of course Facebook also has a lot of leaky behaviors concerning finding friends and friend suggestion. They also value service growth more than privacy, and that's their right.

parennoob• 13 years ago

But 99.9% of their users won't know or care

Exactly. Getting individual users to care about privacy or security is ultimately a cultural thing. In the US (which probably has most of Snapchat's users), the attitude of the general public to this seems to be pretty gung-ho, leading to this being a non-event.

I suspect (but can't be sure) that if something like this happened, in, say, Germany, it would generate far more impact and press attention. Most of my US acquaintances who are college students don't give two hoots about privacy -- they are far too busy marketing themselves to the world as much as possible.

octatone24• 13 years ago

Why is user info presented in the clear to anyone who asks for it via their api?

Here's a more sane approach I imagine:

Allow sending snaps to a phone number (rather than to a username - since you would not know it the time), and attach a "friend request" as part of delivery. When the person at that phone number retrieves the snap they have the additional option of accepting the friend request which then (and only then) exposes their user info to the originating party.

daurnimator2• 13 years ago

via MMS? that would be quite a bit of business AND development effort... (which must be redone for each country of operation)

octatone24• 13 years ago

No, via snapchat's delivery system; they obviously can map a phone number to username, therefor they can implement sending snaps to phone numbers (as a proxy) in place of a username.

tantalor• 13 years ago

Snapchat doesn't use MMS.

maxerickson• 13 years ago

That would be horribly abused (people sending things other people don't much want to look at).

Allowing the friend based on phone numbers might be ok (but you still have to somehow make sure people don't get a bunch of garbage requests).

octatone24• 13 years ago

Leave out the snap sending part, just make it a friend request. Don't expose to the sender whether the number is not attached to account, it is accepted or rejected. User can or can not send snaps then.

chris_wot• 13 years ago

On Christmas Eve, that same group publicly documented our API, making it easier for individuals to abuse our service and violate our Terms of Use.

Security through obscurity? Great way of protecting your users.

It's pathetic that they believe that others haven't already worked out their protocol and were using it.

Funny how they have had to quickly backtrack from this blog post:

http://blog.snapchat.com/post/71353347590/finding-friends-wi...

smackfu• 13 years ago

Did they not have a max phonebook size? Rate limiting doesn't matter if one API call can do it all.

notlisted2• 13 years ago

Wow. Talk about a non-reaction. As if bad code resulting in the disclosure of 4.6MM numbers and IDs is a non-issue.

Posted something about this on FB, achieved zero reactions which really surprised me, until I realized that some think it's only for sexting... and thus nobody is willing to admit they've installed it (it's useful for other stuff as well, I'm my own emoticon).

Several of my friends are in the list (known nicks match known numbers, showing exactly what's the problem here).

Maybe I should post something on their wall? :-)

hindsightbias• 13 years ago

zero reactions

Brave new world. The kids don't care about security, and they don't read their FB.

notlisted2• 13 years ago

Not a kid, nor are most of my friends (many are 29.99999999)

chatmasta• 13 years ago

I'm in college, and I would say 95% of my friends have snapchat. Most of them use it at least once a day. Nobody sends naked pics. Just stuff that you wouldn't necessarily post to facebook. Snapchat's reputation as naked pics only is completely unfounded... it's not like they're sending 450mm nudes every day.

superuser26• 13 years ago

Most people are not offended by the existence of phone books, either.

dannsfw• 13 years ago

"We want to make sure that security experts can get ahold of us when they discover new ways to abuse our service so that we can respond quickly to address those concerns."

"Quickly" is a relative term here, I guess.

Systemic33• 13 years ago

So in a nutshell they are saying that some of their users are risky enough to use a feature that discloses their phone number to them, and they consider this information as non-sensitive data.

Snapchat is and will always just be a fad, it's the current social network flavour of the time, and when something more interesting comes along, I will bet that the 4.6M users will be inactive in no time.

This is also why their users aren't concerned with this leak, because the premise in snapchat is a sort of leaking of your good and bad moments, with no filter. But i'd be pretty sure that if it turns out they save the images and videos, it would be much bigger of a deal, because it ruins this premise.

dsl• 13 years ago

I implemented a "find friends" server side functionality for a mobile app (due to a similar business requirement of allowing new users to locate friends).

After prompting the user for the ok, the mobile app would upload the entire address book to the server. I would check for matches and return a maximum of 25% of total contacts as being valid (randomly so you wouldn't know which numbers really didn't exist). If there were more hits they would be placed into a queue and sent periodically as "your friend has joined!" notices which also increased engagement.

Subsequent checks were done by again uploading the entire address book, however I would check against the previously stored phonebook (numbers only hashed with a per user salt) and limit the number of valid hits returned based on the delta of the address book. So if you kept sending 1000 new numbers every time, you wouldn't get any new matches.

It was also rate limited per account (which required a verified phone number). All the logic took less than a few hours to think up and implement. Here you go Snapchat, now fix your shit.

ch4ch4• 13 years ago

At least you ask the user for permission- Snapchat doesn't even alert the user before uploading the ENTIRE address book!

I take issue with this new generation of developers who seem to have no moral or ethical boundaries on the invasion of privacy.

The whole "viral/social marketing" trend is also to blame, in addition to the way that startup valuation puts so much emphasis on "traction" rather than the actual tech or even a viable business model!

jluxenberg2• 13 years ago

Not true; they prompt and clearly describe what they will do with your address book during onboarding. Can't find a screenshot of it now, and maybe it has changed since they first launched.

thaumaturgy2• 13 years ago

I take issue with this new generation of developers who seem to have no moral or ethical boundaries on the invasion of privacy.

I do too, but I'm beginning to become convinced that most people really don't care and really aren't bothered by it.

We've had numerous clients -- maybe most of them -- request or expect us to keep track of the passwords for their online accounts for them. Privacy erosions and violations by various businesses really haven't been that big of a deal outside of tech circles. Just an hour or so ago, while on an errand, an NPR guest was mentioning something similar, that her Facebook account had been compromised but it didn't change the way she used the service. It wasn't really anything more than a temporary inconvenience for her.

Earlier today, a client's personal Hotmail account was compromised. It was being used to spam people on his contacts list. We got in touch with him to give him the heads-up on it. His response was, "it's not a big deal, I don't really care about that, I'm not even going to change the password on it."

We had one business client that supposedly took security very seriously. Government funded and all that. They would routinely ask us to put new procedures and safeguards in place, only to then turn around and immediately try to work around them for convenience's sake.

This has been a tough thing to accept, but I really don't believe any more that most people care at all about privacy or security. What they mostly want is convenience.

And SnapChat is very convenient.

jluxenberg2• 13 years ago

I think hashing is key here. There are 10^10 possible phone numbers (without country code), so approx 34 bits of information to encode the entire phone number space.

If your API accepts a 128-bit hash (pick your favorite) of a phone number and returns the user's username, and is rate-limited, it would be infeasible to brute force the hashed phone number space to produce the data dump. Then, rate limit by account (rather than IP address) and flag accounts accessing this API too frequently or in different patterns than your client uses.

wahnfrieden3• 13 years ago

You're assuming that the hashing algo used in the app is indecipherable by an attacker - if the hashing algo used is known, then the attacker does the same as done in this SnapChat attack, except just hashing the number first.

daeken• 13 years ago

Hashes never increase the amount of information that's present, thus if there are 10^10 possible phone numbers, there are 10^10 possible hashes of phone numbers (with a given algorithm). How many bits you encode the information in doesn't matter.

The only way you can stop this attack is by rate limiting (I would use some sort of exponential slowdown based on number of requests in a given period) or by not doing it in the first place. It's not hard to determine that if you have a function X -> Y, you can find all the Ys by putting in all the Xs, and correlate the two; that's what's happening here, and it's a privacy trade-off, but not a security issue.

wahnfrieden3• 13 years ago

Tangential, but: we only have "find friends" by email, not phone, but we use a one-way hash of the email for the request so that our servers don't get sent emails that we don't already have, which helps a little though not with the SnapChat issue.

Gurrewe• 13 years ago

I tried to send a snap ( via http://kittenbot.gustav.tv/ ) to all the leaked users. Turns out the app crashes a lot after around 10k friends. :D

nostromo• 13 years ago

It's hard for me to get too worked up over this.

I mean, do phonebooks still exist? They used to list everyone's numbers and their names and addresses and then leave them on everyone's doorstep. This is just a (partial) phone number and username.

About the worst abuse I can think of is that you have someone's username from another service, and you can maybe find their phone number.

This seems mild compared to, say, Facebook allowing you to search by email and find a user's facebook profile.

dudurocha• 13 years ago

That is one of the worst 'apologies' from I startup I've ever read.

There is none " We fucked up, sorry, we're fixing it". They speak of the leak as simple 'hack' like someone who was capable of finding all your friends using facebook and random luck.

I hope they fix this right, and be more apologetic the next time.

teaneedz2• 13 years ago

A 322 word blog post, no apology and 6 instances of the word 'abuse'.

The PR message that Snapchat just sent is not a good one. Their target demographic may not care much, but at the end of the day, this brand just dropped a big ball and lost an opportunity to build something better.

gibsonsecurity3• 13 years ago

We're going to be releasing a statement shortly.

Here: https://gist.github.com/anonymous/8231005

schappim• 13 years ago

"$10 to whoever shows me where the apology is in this. Still looking…" - carpeaqua

So true!

wfraser• 13 years ago

"How dare they tell people about the insecure API we wrote and how it works!"

Find Friends Abuse

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