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Mozilla Foundation Security Advisory 2015-18

Double-free when using non-default memory allocators with a zero-length XHR

February 24, 2015
Abhishek Arya, Gary Kwong
Firefox, SeaMonkey
Fixed in
  • Firefox 36
  • SeaMonkey 2.33


Security researcher Abhishek Arya (Inferno) of the Google Chrome Security Team and Mozilla security developer Gary Kwong used the Address Sanitizer tool to discover a double-free error when sending a zero-length XmlHttpRequest (XHR). This was due to errors in memory allocation when using different memory allocator libraries than jemalloc used by Mozilla builds. When those other memory allocators are used for build compilation, this could cause a potentially exploitable crash during some XHR actions.

This vulnerability does not happen in Firefox as built by Mozilla, but can occur when Firefox is built using a memory allocator that follows older pre-standard behaviors.