JavaScript immutable property enforcement can be bypassed — Mozilla

Mozilla developer Jeff Walden reported that in Gecko's implementation of ECMAScript 5 API's enforces non-configurable properties with logic specific to each API. Scripts that do not go through these APIs can bypass these protections and make changes to the immutable properties in violation of...

Mozilla: Redefinition of non-configurable JavaScript object properties (MFSA 2015-82)

Mozilla Firefox before 40.0 and Firefox ESR 38.x before 38.2 do not impose certain ECMAScript 6 requirements on JavaScript object properties, which allows remote attackers to bypass the Same Origin Policy via the reviver parameter to the JSON.parse method...

Redefinition of non-configurable JavaScript object properties — Mozilla

Security researcher André Bargull reported non-configurable properties on JavaScript objects can be redefined while parsing JSON in violation of the ECMAScript 6 standard. This allows malicious web content to bypass same-origin policy by editing these properties to arbitrary values...