The Javascript engine in Opera 7.23 allows remote attackers to cause a denial of service (crash) by creating a new Array object with a large size value, then writing into that array.

Opera 7.50 and earlier allows remote web sites to provide a "Shortcut Icon" (favicon) that is wider than expected, which could allow the web sites to spoof a trusted domain and facilitate phishing attacks using a wide icon and extra spaces.

Opera 8.01 allows remote attackers to conduct cross-site scripting (XSS) attacks or modify which files are uploaded by tricking a user into dragging an image that is a "javascript:" URI.

Opera allows remote attackers to cause a denial of service (invalid memory reference and application crash) via a web page or HTML email that contains a TBODY tag with a large COL SPAN value, as demonstrated by mangleme.

Opera 8.01, when the "Arial Unicode MS" font (ARIALUNI.TTF) is installed, does not properly handle extended ASCII characters in the file download dialog box, which allows remote attackers to spoof file extensions and possibly trick users into executing arbitrary code.

Heap-based buffer overflow in Opera 7.11 and 7.20 allows remote attackers to execute arbitrary code via an HREF with a large number of escaped characters in the server name.

Opera 8.01 allows remote attackers to cause a denial of service (CPU consumption) via a crafted JPEG image, as demonstrated using random.jpg.

Argument injection vulnerability in Opera before 7.50 does not properly filter "-" characters that begin a hostname in a telnet URI, which allows remote attackers to insert options to the resulting command line and overwrite arbitrary files via (1) the "-f" option on Windows XP or (2) the "-n" option on Linux.

Opera 7.x and 8 before 8.01 does not clearly associate a Javascript dialog box with the web page that generated it, which allows remote attackers to spoof a dialog box from a trusted site and facilitates phishing attacks, aka the "Dialog Origin Spoofing Vulnerability."

Opera 7.54 and earlier uses kfmclient exec to handle unknown MIME types, which allows remote attackers to execute arbitrary code via a shortcut or launcher that contains an Exec entry.

Buffer overflow in Opera 7.02 Build 2668 allows remote attackers to crash Opera via a long HTTP request ending in a .ZIP extension.

Opera Mini 13 and Opera Stable 36 allow remote attackers to spoof the displayed URL via a crafted HTML document, related to the about:blank URL.

Characters from languages are such as Arabic, Hebrew are displayed from RTL (Right To Left) order in Opera 37.0.2192.105088 for Android, due to mishandling of several unicode characters such as U+FE70, U+0622, U+0623 etc and how they are rendered combined with (first strong character) such as an IP address or alphabet could lead to a spoofed URL. It was noticed that by placing neutral characters such as "/", "?" in filepath causes the URL to be flipped and displayed from Right To Left. However, in order for the URL to be spoofed the URL must begin with an IP address followed by neutral characters as omnibox considers IP address to be combination of punctuation and numbers and since LTR (Left To Right) direction is not properly enforced, this causes the entire URL to be treated and rendered from RTL (Right To Left). However, it doesn't have be an IP address, what matters is that first strong character (generally, alphabetic character) in the URL must be an RTL character.

HTTP/2: HEIST attack allows attackers to sniff TLS encrypted HTTP/2 traffic

The HTTP/2 protocol does not consider the role of the TCP congestion window in providing information about content length, which makes it easier for remote attackers to obtain cleartext data by leveraging a web-browser configuration in which third-party cookies are sent, aka a "HEIST" attack.

The TLS protocol 1.2 and earlier supports the rsa_fixed_dh, dss_fixed_dh, rsa_fixed_ecdh, and ecdsa_fixed_ecdh values for ClientCertificateType but does not directly document the ability to compute the master secret in certain situations with a client secret key and server public key but not a server secret key, which makes it easier for man-in-the-middle attackers to spoof TLS servers by leveraging knowledge of the secret key for an arbitrary installed client X.509 certificate, aka the "Key Compromise Impersonation (KCI)" issue.

Opera before 10.61 does not properly suppress clicks on download dialogs that became visible after a recent tab change, which allows remote attackers to conduct clickjacking attacks, and consequently execute arbitrary code, via vectors involving (1) closing a tab or (2) hiding a tab, a related issue to CVE-2005-2407.

Opera does not properly manage the address bar between the request to open a URL and the retrieval of the new document's content, which might allow remote attackers to conduct spoofing attacks via a crafted HTML document, a related issue to CVE-2010-1206.

Multiple unspecified vulnerabilities in Opera before 10.54 have unknown impact and attack vectors related to (1) "extremely severe," (2) "highly severe," (3) "moderately severe," and (4) "less severe" issues.

Opera 9.52 allows remote attackers to cause a denial of service (resource consumption) via JavaScript code containing an infinite loop that creates IFRAME elements for invalid (1) news:// or (2) nntp:// URIs.

Opera 9.52 does not properly handle an IFRAME element with a mailto: URL in its SRC attribute, which allows remote attackers to cause a denial of service (resource consumption) via an HTML document with many IFRAME elements.