The instanceof operator can bypass the Xray wrapper mechanism. When called on web content from the browser itself or an extension the web content can provide its own result for that operator, possibly tricking the browser or extension into mishandling the element. This vulnerability affects Firefox < 56.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Firefox | Mozilla | * | 55.0.3 (including) |
| Firefox | Ubuntu | artful | * |
| Firefox | Ubuntu | bionic | * |
| Firefox | Ubuntu | devel | * |
| Firefox | Ubuntu | trusty | * |
| Firefox | Ubuntu | upstream | * |
| Firefox | Ubuntu | xenial | * |
| Firefox | Ubuntu | zesty | * |