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While playing a challenge by Salvatore Abello, I found a pretty interesting way to exploit Dangling Markup with a strict CSP. All you need is an <iframe>, <object> or <embed> set to about:blank, with a dangling name= attribute. This vulnerable page should be iframable.

On our attacker's page, we load this in an iframe and can then access [0] to get a reference to our injected object. To read its name, we can set its location to *our* about:blank and then read the .name window property (set by the attribute)!