A use-after-free vulnerability can occur in the chrome event handler when it is freed while still in use. This results in a potentially exploitable crash.

A vulnerability where a JavaScript compartment mismatch can occur while working with the fetch API, resulting in a potentially exploitable crash.

Images from a different domain can be read using a canvas object in some circumstances. This could be used to steal image data from a different site in violation of same-origin policy.

A possible vulnerability exists where type confusion can occur when manipulating JavaScript objects in object groups, allowing for the bypassing of security checks within these groups. Note: this vulnerability has only been demonstrated with UnboxedObjects, which are disabled by default on all supported releases.

If hyperthreading is not disabled, a timing attack vulnerability exists, similar to previous Spectre attacks. Apple has shipped macOS 10.14.5 with an option to disable hyperthreading in applications running untrusted code in a thread through a new sysctl. Firefox now makes use of it on the main thread and any worker threads. Note: users need to update to macOS 10.14.5 in order to take advantage of this change.

Incorrect handling of __proto__ mutations may lead to type confusion in IonMonkey JIT code and can be leveraged for arbitrary memory read and write.

As part of his winning Pwn2Own entry, Niklas Baumstark demonstrated a sandbox escape by installing a malicious language pack and then opening a browser feature that used the compromised translation.

Firefox will accept any registered Program ID as an external protocol handler and offer to launch this local application when given a matching URL on Windows operating systems. This should only happen if the program has specifically registered itself as a "URL Handler" in the Windows registry. Note: This issue only affects Windows operating systems. Other operating systems are unaffected.

Mozilla developers and community members Olli Pettay, Bogdan Tara, Jan de Mooij, Jason Kratzer, Jan Varga, Gary Kwong, Tim Guan-tin Chien, Tyson Smith, Ronald Crane, and Ted Campbell reported memory safety bugs present in Firefox 66 and Firefox ESR 60.6. Some of these bugs showed evidence of memory corruption and we presume that with enough effort that some of these could be exploited to run arbitrary code.

A use-after-free vulnerability can occur when the SMIL animation controller incorrectly registers with the refresh driver twice when only a single registration is expected. When a registration is later freed with the removal of the animation controller element, the refresh driver incorrectly leaves a dangling pointer to the driver's observer array.