Comcast Xfinity Web Flaws Exposed Customer Data

There is no comfortable way for an organisation to learn that its website is leaking customer data but one of the most alarming must surely be getting that bad news from a journalist.

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This is what appears to have happened to US communications giant Comcast Xfinity, which has had to patch two significant web vulnerabilities after Buzzfeed News learned of the issues from researcher Ryan Stevenson.

Flaw #1

The first was found on the in-home authentication page through which customers can pay bills without the inconvenience of having to log in.

It seems the company authenticated users by asking them to choose their home address from one of four possibilities, selected by looking at one of the headers added to the HTTP request.

The HTTP header used to “identify” the user contained their public-facing Comcast IP address – data that isn’t suitable to use as a secret identifier.

An attacker who knew your IP number could therefore insert it into their own web requests, and keep refreshing the identification page – each time they refreshed, the list of home addresses returned would include your address plus three randomly chosen other addresses.

Flaw #2

The second issue, which builds on the first, was found on a sign-up page for Comcast authorised retailers.

Having used the first vulnerability to gain access to a customer’s address from their IP number, this page could allow an attacker to enter this to carry out a brute force attack to discover the last four digits of their US social security number (SSN).

After entering a valid address, an attacker could cycle through all 10,000 four-digit numbers (0000-9999) until one of them turned out to be the four digits that matched the customer’s SSN – there was no limit on the number of guesses or the speed at which they could be tried.

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