XSS in Apple ID Server idmsa.apple.com

[Zemn mez <zemnmez () gmail com>]

Hi seclists! I wanted to try posting some of my research here, and I think
this is the right list.

I recently published some research into Apple ID security that culminated
in an XSS on the Apple ID server -- that is, an attacker can pop out an
Apple login page that autofills your credentials and 2FA :)

In particular, it has several really interesting components in the chain:

- a Content Security Policy injection / bypass to slacken Javascript code
execution and embed restrictions
- bypass to postMessage restrictions on sending and receiving messages that
uses some deep diving into the relevant spec
- several bugs that involve interpretation malleability of URLs

I was surprised to find out that postMessage's 'targetOrigin' parameter
does not, as the spec describes, take a target origin, but actually a
target *URL* which is then *parsed* to extract an origin. This means that,
say 'https://nonsense:morenonsense () apple com/somepath?nonsense#nonsense' as
a *targetOrigin* will match 'https://apple.com'.

The full write-up can be found here:
https://zemnmez.medium.com/how-to-hack-apple-id-f3cc9b483a41

Thomas

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