A flaw in LinkedIn feature allowed user data harvesting

The researcher Jack Cable (18) has discovered a vulnerability in LinkedIn, the AutoFill functionality, that allowed user data harvesting.

While experts and people are discussing the Cambridge Analytica case another disconcerting case made the headlines, the private intelligence agency LocalBlox has left unsecured online an AWS bucket containing 48 million records that were also harvested from Facebook, LinkedIn, and Twitter.

No doubt, data harvesting is a common practice and we are only discovering the tip of the iceberg, many companies and intelligence agencies do it for different reasons.

Sometimes this activity is advantaged by security flaws in the features implemented by the social media platforms.

Early April, Mark Zuckerberg admitted public data of its 2.2 billion users has been compromised over the course of several years by third-party actors that gathered information on its users. Third-party scrapers have exploited an issue in the Facebook’s search function that allows anyone to look up users via their email address or phone numbers.

Now the researcher Jack Cable (18) has discovered a flaw in LinkedIn, the AutoFill functionality, that allowed user data harvesting.

The AutoFill functionality allows to quickly fill out forms with data from their LinkedIn profile, including name, title, company, email address, phone number, city, zip code, state, and country.

Cable explained that it is possible to exploit the function to harvest user data by placing the AutoFill button on a malicious website, rather than leaving the LinkedIn button visible on the page the attacker could have changed its properties and locate it everywhere in the page making it invisible.

With this trick, that clearly violates LinkedIn’s privacy policies, when a user would visit the malicious site and click anywhere on the page, it unawares clicks on the invisible AutoFill button, resulting in his LinkedIn data being harvested.

“The potential for exploitation existed until being patched 04/19/18, as any whitelisted website can access this information with a single click.” wrote Cable.

“The exploit flowed as follows:

1. The user visits the malicious site, which loads the LinkedIn AutoFill button iframe.
2. The iframe is styled so it takes up the entire page and is invisible to the user.
3. The user clicks anywhere on the page. LinkedIn interprets this as the AutoFill button being pressed, and sends the information via postMessage to the malicious site.
4. The site harvests the user’s information via the following code:

window.addEventListener("message", receiveMessage, false);

function receiveMessage(event)
{
  if (event.origin == 'https://www.linkedin.com') {
    let data = JSON.parse(event.data).data;
    if (data.email) {
      alert('Hi, ' + data.firstname + ' ' + data.lastname + '! Your email is ' + data.email + '. You work at ' + data.company + ' and you live in ' + data.city + ', ' + data.state + '.');
      console.log(data);
    }
  }
  console.log(event)
}

“

Cable pointed out with this trick it is possible to access also non-public data was also provided to a site abusing AutoFill function, even if LinkedIn states in its documentation that only public data is provided to fill out forms.

Cable reported the flaw to LinkedIn on April 9 and the company temporary restricted the AutoFill functionality to whitelisted sites. Of course, the problem was not completely addressed in this way, an attacker that was able to compromise the whitelisted site was still in position to harvest data from LinkedIn.

On April 19, LinkedIn published a stable fix for the issue.

LinkedIn said it is not aware of there had been no evidence of malicious exploitation, but I’m sure that many of view has a different opinion.

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Pierluigi Paganini

(Security Affairs – LinkedIn, data harvesting)

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