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.
El operador "instanceof" puede omitir el mecanismo del wrapper Xray. Cuando se le llama en un contenido web desde el propio navegador o una extensión, el contenido web puede proporcionar su propio resultado para ese operador, pudiendo engañar al navegador o extensión para que manipule erróneamente el elemento. Esta vulnerabilidad afecta a las versiones anteriores a la 56 de Firefox.
USN-3435-1 fixed vulnerabilities in Firefox. The update caused the Flash plugin to crash in some circumstances. This update fixes the problem. Multiple security issues were discovered in Firefox. If a user were tricked in to opening a specially crafted website, an attacker could potentially exploit these to read uninitialized memory, obtain sensitive information, bypass phishing and malware protection, spoof the origin in modal dialogs, conduct cross-site scripting attacks, cause a denial of service via application crash, or execute arbitrary code. Martin Thomson discovered that NSS incorrectly generated handshake hashes. A remote attacker could potentially exploit this to cause a denial of service via application crash, or execute arbitrary code. Multiple security issues were discovered in WebExtensions. If a user were tricked in to installing a specially crafted extension, an attacker could potentially exploit these to download and open non-executable files without interaction, or obtain elevated privileges. Various other issues were also addressed.
