Opera before 12.01 on Windows and UNIX, and before 11.66 and 12.x before 12.01 on Mac OS X, does not properly escape characters in DOM elements, which makes it easier for remote attackers to bypass cross-site scripting (XSS) protection mechanisms via a crafted HTML document.

Opera before 12.01 allows remote attackers to cause a denial of service (application crash) via a crafted web site, as demonstrated by the Lenovo "Shop now" page.

Opera before 12.01 on Windows and UNIX, and before 11.66 and 12.x before 12.01 on Mac OS X, ignores some characters in HTML documents in unspecified circumstances, which makes it easier for remote attackers to conduct cross-site scripting (XSS) attacks via a crafted document.

Opera before 12.00 Beta allows remote attackers to cause a denial of service (memory consumption or application hang) via an IFRAME element that uses the src="#" syntax to embed a parent document.

Unspecified vulnerability in Opera before 12.00 on Mac OS X has unknown impact and attack vectors, related to a "moderate severity issue."

Opera before 12.00 Beta allows remote attackers to cause a denial of service (application crash) via a web page that contains invalid character encodings.

Opera before 12.00 Beta allows remote attackers to cause a denial of service (application crash) via crafted characters in domain names, as demonstrated by "IDNA2008 tests."

Opera before 12.00 Beta allows remote attackers to cause a denial of service (application crash) via crafted WebGL content, as demonstrated by a codeflow.org WebGL demo.

Opera before 11.65 does not ensure that the address field corresponds to the displayed web page during blocked navigation, which makes it easier for remote attackers to conduct spoofing attacks by detecting and preventing attempts to load a different web page.

Opera before 12.00 Beta allows user-assisted remote attackers to cause a denial of service (application hang) via JavaScript code that changes a form before submission.