URLs using “javascript:” have the protocol removed when pasted into the address bar to protect users from cross-site scripting (XSS) attacks, but in certain circumstances this removal was not performed. This could allow users to be socially engineered to run an XSS attack against themselves. This vulnerability affects Opera for Android versions below 61.0.3076.56532.

The HTML parsing engine in Opera before 9.63 allows remote attackers to execute arbitrary code via crafted web pages that trigger an invalid pointer calculation and heap corruption.

Cross-site scripting (XSS) vulnerability in Opera.dll in Opera before 9.61 allows remote attackers to inject arbitrary web script or HTML via the anchor identifier (aka the "optional fragment"), which is not properly escaped before storage in the History Search database (aka md.dat).

Opera allows web sites to set cookies for country-specific top-level domains that have DNS A records, such as co.tv, which could allow remote attackers to perform a session fixation attack and hijack a user's HTTP session, aka "Cross-Site Cooking."

Opera, probably before 7.50, sends Referer headers containing https:// URLs in requests for http:// URLs, which allows remote attackers to obtain potentially sensitive information by reading Referer log data.