Report Exposes Flaws In Link Shorteners That Reveal Sensitive Info About Users And Track Their Offline Movements

from the sna.fu dept

URL shorteners: not just for malware/spam delivery anymore!

TL;DR: short URLs produced by,, and similar services are so short that they can be scanned by brute force. Our scan discovered a large number of Microsoft OneDrive accounts with private documents. Many of these accounts are unlocked and allow anyone to inject malware that will be automatically downloaded to users’ devices. We also discovered many driving directions that reveal sensitive information for identifiable individuals, including their visits to specialized medical facilities, prisons, and adult establishments.

The Freedom to Tinker Foundation has just released a study it compiled over the last 18 months — one in which it scanned thousands of shortened URLs and discovered what they unintentionally revealed. Microsoft’s OneDrive — which uses link-shortening — could be made to reveal documents uploaders never intended to share with the public. Worse, Freedom to Tinker discovered a small percentage of brute-forced URLs linked to documents with “write” privileges enabled.

Around 7% of the OneDrive folders discovered in this fashion allow writing. This means that anyone who randomly scans URLs will find thousands of unlocked OneDrive folders and can modify existing files in them or upload arbitrary content, potentially including malware.

And, because Microsoft’s automatic virus/malware scanning for OneDrive contents is less than robust, it wouldn’t take much for any random person to wreak havoc on any number of devices with access to those contents.

OneDrive “synchronizes” account contents across the user’s OneDrive clients. Therefore, the injected malware will be automatically downloaded to all of the user’s machines and devices running OneDrive.

Fortunately for OneDrive users, the scanning method deployed by FTTF no longer works as of March 2016. But this doesn’t necessarily mean the accounts are completely secure — just that one avenue for attack/access has been closed.

Just as disturbing — but for different reasons — is the automatic link shortening tied to Google Maps. The links could be manipulated to discover all sorts of inferential information about people’s private activities… or at least the activities they never thought they were sharing with the world. The directions and searches uncovered by FTTF’s scanning activity potentially reveal plenty of sensitive information about Google Maps users.

Our sample random scan of these URLs yielded 23,965,718 live links, of which 10% were for maps with driving directions. These include directions to and from many sensitive locations: clinics for specific diseases (including cancer and mental diseases), addiction treatment centers, abortion providers, correctional and juvenile detention facilities, payday and car-title lenders, gentlemen’s clubs, etc. The endpoints of driving directions often contain enough information (e.g., addresses of single-family residences) to uniquely identify the individuals who requested the directions. For instance, when analyzing one such endpoint, we uncovered the address, full name, and age of a young woman who shared directions to a planned parenthood facility.

The same privacy concerns associated with the indiscriminate use of automatic license plate readers by law enforcement and warrantless access to cell site location info are present here: the reconstruction of people’s lives via the “tracking” of their movements. In this case, however, the information generated is more “voluntary” than either of the other listed collections, which are far more passive than searching for directions using a web service provided by a company with an unquenchable thirst for data.

The good news is that the method deployed for the report no longer works for Google Maps-shortened links. But, once again, that does not mean the problems with link shorteners have been eliminated. FTTF points out that the March 2016 change by Microsoft (which claims it had nothing to do with FTTF reporting the vulnerability to it) only affects links generated after that date. Any previous short URLs are still vulnerable to traversal scans.

Google, however, did make a more of a serious attempt to prevent abuse of its shortened links.

All newly generated URLs have 11- or 12-character tokens, and Google deployed defenses to limit the scanning of the existing URLs.

While this news should be of concern to users of these services, it definitely has to be great news for law enforcement and intelligence agencies. So much for “going dark.” Vulnerabilities in web services apparently provide access to otherwise “locked” cloud storage contents and Google Maps — at least until it was fixed — generating tons of location data for the taking.

It’s also worth pointing out that the method used by Freedom to Tinker to complile this report is basically the same method used by Andrew “Weev” Auernheimer to expose AT&T users’ email addresses: altering URLs to uncover data presumed to be hidden. Of course, AT&T’s vindictiveness resulted in a 3.5 year prison sentence for Auernheimer. No legal threats have been made towards FTTF, but the sad thing is that security research is inherently risky, as you can never tell whether the entity affected will respond with a bug fix or a police report — not until after they’ve been informed.

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Companies: google, microsoft

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Comments on “Report Exposes Flaws In Link Shorteners That Reveal Sensitive Info About Users And Track Their Offline Movements”

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Anonymous Coward says:

Re: Feynmann

It may not be new, but it is still a problem. If security research were less risky, you might have more white hats working on it and disclosing the information to the affected vendors. As is, an unknown number of technically competent researchers are not reporting, and may even be avoiding attempting to discover, vulnerabilities because they do not want to deal with the hostile responses. When I see people contemplating an attempt to find a vulnerability, I actively remind them to consider the potential for hostile responses before they embark on the research.

Personally, I make it a point not to explore things that look like they might be weak, because I cannot prove the weakness without it looking like a hack attack if someone is monitoring the target.

Bob Webster (profile) says:

It’s hard to believe so many people consider the use of shortened URLs a security measure. It is not, and was never intended to be. A URL is exposed, by definition, whether long or shortened. A shortened URL is a convenience, not a security tool. Some people misuse base64 encoding for “security” as well, but it does not mean we should get rid of base64 encoding.

PRMan (profile) says:


The article suggests lengthening as the solution. Really?

The whole point is that these are short enough for Twitter.

I suggest in 7-character, they start using the whole keyspace instead of a 1 at the front of another 6-character keyspace. That would help.

But it was odd to me that all the suggestions were pointed toward the shortening providers, as if the users had no responsibility whatsoever.

How about:

1) Don’t put your documents in the cloud.
2) If you do put your documents in the cloud, OneDrive isn’t secure.
3) Don’t make shortened URLs to your documents. And don’t share document URLs online.

Anonymous Coward says:

Re: Lengthening?

1) Don’t put your documents in the cloud.

That requires that people cam either get a fixed IP address for their home connection, or use a dynamic DNS services to allow use of a private server. Also, if using windows it is a right pain to set up to use SSH for a secure connection to a home server. It almost as if the the proprietary operating system vendors and ISPs are doing their best to ensure that private individuals cannot have any privacy.

John Fenderson (profile) says:

Re: Re: Lengthening?

“That requires that people cam either get a fixed IP address for their home connection, or use a dynamic DNS services to allow use of a private server”

Not as much as you might think. While it’s true that your dynamic IP address can change, in practice it rarely actually does. And it almost never changes unless you disconnect and reconnect.

I know a lot of people who run an SSH server from their home machines for remote access, but don’t have a dedicated IP and don’t use DDNS services.

“if using windows it is a right pain to set up to use SSH for a secure connection to a home server.”

This is just not true. Perhaps it used to be years ago, but setting this up on Windows now is pretty simple. It takes about 5 minutes.

Jeremy Lyman (profile) says:

Loose Lips

“the address, full name, and age of a young woman who shared directions”

Not necessarily. When I share links to directions I hardly ever put where I am in them. Most times they contain where my friend is starting and where they want to go. So this may be the address of a young woman whose friend punched her information into Google and exposed her to a privacy violation. Which is arguably a bit worse.

Jeremy Lyman (profile) says:

Re: Re: Loose Lips

Off the top of my head I can think of exercise routes on trails or roads that hit a certain mileage, or a detour that takes a road not naturally recommended. Sometimes addresses can be geolocated incorrectly so you might use lat/long coordinates instead. I’m sure there are other reasons beyond just generally being helpful.

The main point is that it’s something people do, whether there’s a good reason or not, and something that google specifically encourages with a checkbox.

Anonymous Coward says:

Re: Re: Re: Loose Lips

Maybe I’ not parsing your previous comment correctly, but it sounds like you said you do things that in the next sentence you consider a privacy violation. Or do you always ask for consent first before entering other’s location data into a public service?

It’s totally okay if you received informed consent to use data in that way, but if these are things we consider important shouldn’t we strive to protect everyone’s data not just our own?

Jeremy Lyman (profile) says:

Re: Re: Re:2 Loose Lips

Ah, I see! Sure, my behavior could be considered that way. I was just using my experience to point out that the personally identifiable information (pii) they gathered wasn’t necessarily submitted by that person.

I don’t generally use url shorteners or route people to medical facilities, so my friends should be okay. But it’s something that most people probably don’t consider; these services take a snapshot of your private browsing history (whatever information is currently in url parameters) and make it publicly accessible and discover-able.

Uriel-238 (profile) says:

So I can still use shorteners...

…to link to YouTube videos and Wikipedia articles, but might not want to trust other people’s shortened links. Yes?

Of course, the only reason I have generally to use short URLs is if I were posting links on Twitter.

For anything else with less sparse space, I use DDG Bangs. Exempli gratia:!w!i

Why doesn’t Techdirt have a moe-tan anthro mascot? Do you not love Japan?

Rich Kulawiec (profile) says:

"link shorteners" are scams and abuse magnets

I’ve had a blacklist-on-sight policy in place for them for years and strongly recommend the same to everyone else. Most of them are scams; most of them are run by spammer and phishers and equally filthy scumbags; and NONE of them does even a token job of abuse control. (Of course they don’t: abuse is their business model.)

John Fenderson (profile) says:

Link shorteners are a terrible idea

The flaw being discussed here is one problem with them. However, there are (at least) two additional problems that are at least as bad:

1. They eliminate transparency. It’s impossible to know where the link goes without clicking on it. This is 100% unacceptable and makes it trivially easy to trick people into clicking malicious links.

2. They unnecessarily involve a third party who now has access to which IP addresses are requesting which links.

Personally, I never follow links that go through a shortener and I urge others to follow the same practice.

Wendy Cockcroft (user link) says:

Re: Link shorteners are a terrible idea

I get what you’re saying, John, but when the link is really long it’s handy to have a shortener. What if the shortening service scanned the URL for malware, then added a title attribute so that, when you hovered your mouse over it, the actual destination would display in a little box?

E.g. my Medium account.

John Fenderson (profile) says:

Re: Re: Link shorteners are a terrible idea

I totally understand the convenience and utility of link shorteners! But I’m arguing that the benefit is generally not worth the cost.

As to using malware scanners, that would be better than nothing, but malware scanners are not anywhere near good enough to be an adequate solution by themselves.

Adding an attribute that tells you the real URL is a bit pointless because that means that the real URL has to be encoded, so you aren’t saving any bytes — you’re actually increasing the number of bytes required because you have to include both the shortened link and the unshortened link. Also, it is a weak move because the URL you’d see would not be the one in use. You are effectively having to take the service’s word for it, which means that it’s a point of failure that when exploited would make everything even more dangerous by giving you a false sense of comfort.

Also, the problem of unnecessary data leakage remains unaffected by those proposed solutions.

The entire point of link shorteners is one of obfuscation: hide the real URL while presenting you with a shorter encoded one. In my opinion, this is an unacceptably risky proposition.

There is one situation where I’m completely comfortable with them, though: if I were the one running the shortening service, then I’d be much more comfortable with using it, because I retain in control of my data and I can do security audits.

Jeremy Lyman (profile) says:

Re: Re: Re: Link shorteners are a terrible idea

Yup! I’m much more likely to set up a redirect page on one of my domains than use a shortening service. Not in response to any specific flaw, but because I get to decide how long the url is active and I can even assign it a meaningful address. It’s obviously not for everyone, but can be handy if you’re able.

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