Privilege escalation via DOM property overrides
- April 15, 2005
- Firefox, Mozilla Suite
- Fixed in
- Firefox 1.0.3
- Mozilla Suite 1.7.7
moz_bug_r_a4 reported several exploits giving an attacker the ability to install malicious code or steal data, requiring only that the user do commonplace actions like click on a link or open the context menu. The common cause in each case was privileged UI code ("chrome") being overly trusting of DOM nodes from the content window. Scripts in the web page can override properties and methods of DOM nodes and shadow the native values, unless steps are taken to get the true underlying values.
We found that most extensions also interacted with content DOM in a natural, but unsafe, manner. Changes were made so that chrome code using this natural DOM coding style will now automatically use the native DOM value if it exists without having to use cumbersome wrapper objects.
Most of the specific exploits involved tricking the privileged code into calling eval() on an attacker-supplied script string, or the equivalent using the Script() object. Checks were added in the security manager to make sure eval and Script objects are run with the privileges of the context that created them, not the potentially elevated privileges of the context calling them.