Mozilla Foundation Security Advisory 2015-95
Add-on notification bypass through data URLs
- Announced
- August 27, 2015
- Reporter
- Bas Venis
- Impact
- High
- Products
- Firefox, Firefox ESR, SeaMonkey
- Fixed in
-
- Firefox 40.0.3
- Firefox ESR 38.2.1
- SeaMonkey 2.35
Description
Security researcher Bas Venis reported a mechanism where add-ons could
be installed from a different source than user expectations. Normally, when a user enters
the URL to an add-on directly in the addressbar, warning prompts are bypassed because it
is the result of direct user action. He discovered that a data: URL could be
manipulated on a loaded page to simulate this direct user input of the add-on's URL, which
would result in a bypassing of the install permission prompt. He also reported that in the
absence of the permission prompt, it is possible to cause the actual installation prompt
to appear above another site's location by causing a page navigation immediately after
triggering add-on installation. This could manipulate a user into falsely believing a
trusted site (such as addons.mozilla.org) has
initiated the installation. This could lead to users installing an add-on from a malicious
source.