Security Experts:

LinkedIn Vulnerability Allowed User Data Harvesting

LinkedIn recently patched a vulnerability that could have been exploited by malicious websites to harvest data from users’ profiles, including private information.

The flaw affected the AutoFill functionality, which allows websites to offer users the possibility to quickly fill out forms with data from their LinkedIn profile. Users simply click the AutoFill button on a webpage containing a form and some of the fields are pre-populated with data available from LinkedIn, including name, title, company, email address, phone number, city, zip code, state and country.

Jack Cable, an 18-year-old researcher based in Chicago, noticed that this functionality could have been abused to harvest user data by placing the AutoFill button on a malicious site. Rather than leaving the button as provided by LinkedIn, an attacker could have changed its properties to spread it across the entire web page and make it invisible.

Whenever a user would visit the malicious site and click anywhere on the page, they would actually be clicking on the invisible AutoFill button, resulting in their LinkedIn data being harvested by the website.

Cable pointed out that the possibility to launch these types of attacks clearly violated LinkedIn’s policies related to the use of AutoFill. First of all, the social media giant does not allow form field data to be submitted without being seen by the user.

Secondly, while some of the exposed data was publicly accessible on users’ LinkedIn profiles, non-public data was also provided to a site abusing AutoFill. LinkedIn states in its documentation that only public data is used to fill out forms.

Cable reported the vulnerability to LinkedIn on April 9 and a temporary solution that involved restricting the AutoFill functionality to whitelisted sites was rolled out the next day. However, the researcher argued that this fix was incomplete as whitelisted websites still could have collected user data. Furthermore, there was also the possibility of a whitelisted site getting compromised and abused for data harvesting.

LinkedIn rolled out a more permanent fix on April 19. Bleeping Computer reports that users are now prompted whenever their data is being sent to a website via the AutoFill functionality. The social media company said there had been no evidence of malicious exploitation.

While the vulnerability itself is not particularly sophisticated, the existence of such security holes can pose a serious problem to both a company and its customers, as demonstrated by the recent Cambridge Analytica scandal, in which the data of as many as 87 million Facebook users was harvested.

Cable has also reported vulnerabilities to Google, Yahoo, Uber, the U.S. Department of Defense (Hack the Air Force), and many other organizations.

Related: Russian Arrested by Czech Police Tied to 2012 LinkedIn Hack

Related: LinkedIn Patches Persistent XSS Flaw in Help Center

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.