Many times you have seen banners (Flash ads) on websites, where, when you move your mouse over the banner (without clicking it), you see how an animation in the banner starts moving toward your mouse position...

That means that the Flash banner is interactive, without asking our permission. Is there any security threat? E.g. to read not only mouse position, but also other browsers parameters such as cookies?

I don't see any special danger in the behavior you describe. Acting based on mouse over events instead of only clicking without specifically asking for permission is a common practice not only for ads and not only for flash. For example it is used to show detailed information when hovering over a tag on a question on this site.

Apart from that flash is known to be a security risk by itself and ads are too considered risky because of malvertising. You might reduce this risk by blocking flash and ads.

  • Flash is a risk in itself, and is largely being deprecated (for example, most video sites now use HTML5 video instead of a flash-based player). A lot of people block flash as it's rarely used to deliver anything of value. – John U Mar 2 '17 at 13:34
  • @JohnU: I'm not sure what the goal of your comment is since it basically repeats what I'm saying in the answer: flash is a risk by itself and should be blocked. – Steffen Ullrich Mar 2 '17 at 13:36
  • TL;DR: 1.Agreeing with you. 2.It's becoming deprecated, 3. It's rarely used for "good" content. How's that? – John U Mar 2 '17 at 16:51

It depends on a lot of things. If the AD is in an iframe it shouldn't be able to read your cookies on the important site. Anyway there are a lot of flash vulnerabilities and exploit-kits will likely use Flash exploits if your flash player is outdated. Also one can use flash to help fingerprinting the browser, e.g.: font enumeration. So yes, it can be a security threat, but not in the way you assumed.

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