May 20, 2018

Website operators are in the dark about privacy violations by third-party scripts

by Steven Englehardt, Gunes Acar, and Arvind Narayanan.

Recently we revealed that “session replay” scripts on websites record everything you do, like someone looking over your shoulder, and send it to third-party servers. This en-masse data exfiltration inevitably scoops up sensitive, personal information — in real time, as you type it. We released the data behind our findings, including a list of 8,000 sites on which we observed session-replay scripts recording user data.

As one case study of these 8,000 sites, we found health conditions and prescription data being exfiltrated from walgreens.com. These are considered Protected Health Information under HIPAA. The number of affected sites is immense; contacting all of them and quantifying the severity of the privacy problems is beyond our means. We encourage you to check out our data release and hold your favorite websites accountable.

Student data exfiltration on Gradescope

As one example, a pair of researchers at UC San Diego read our study and then noticed that Gradescope, a website they used for grading assignments, embeds FullStory, one of the session replay scripts we analyzed. We investigated, and sure enough, we found that student names and emails, student grades, and instructor comments on students were being sent to FullStory’s servers. This is considered Student Data under FERPA (US educational privacy law). Ironically, Princeton’s own Information Security course was also affected. We notified Gradescope of our findings, and they removed FullStory from their website within a few hours.
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No boundaries: Exfiltration of personal data by session-replay scripts

This is the first post in our “No Boundaries” series, in which we reveal how third-party scripts on websites have been extracting personal information in increasingly intrusive ways. [0]
by Steven Englehardt, Gunes Acar, and Arvind Narayanan

Update: we’ve released our data — the list of sites with session-replay scripts, and the sites where we’ve confirmed recording by third parties.

You may know that most websites have third-party analytics scripts that record which pages you visit and the searches you make.  But lately, more and more sites use “session replay” scripts. These scripts record your keystrokes, mouse movements, and scrolling behavior, along with the entire contents of the pages you visit, and send them to third-party servers. Unlike typical analytics services that provide aggregate statistics, these scripts are intended for the recording and playback of individual browsing sessions, as if someone is looking over your shoulder.

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