Opera before 57.0.3098.106 is vulnerable to a DLL Search Order hijacking attack where an attacker can send a ZIP archive composed of an HTML page along with a malicious DLL to the target. Once the document is opened, it may allow the attacker to take full control of the system from any location within the system. The issue lies in the loading of the shcore.dll and dcomp.dll files: these files are being searched for by the program in the same system-wide directory where the HTML file is executed.

In the WebRTC component in Opera 51.0.2830.55, after visiting a web site that attempts to gather complete client information (such as https://ip.voidsec.com), the browser can disclose a private IP address in a STUN request.

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.

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, when a DHE_EXPORT ciphersuite is enabled on a server but not on a client, does not properly convey a DHE_EXPORT choice, which allows man-in-the-middle attackers to conduct cipher-downgrade attacks by rewriting a ClientHello with DHE replaced by DHE_EXPORT and then rewriting a ServerHello with DHE_EXPORT replaced by DHE, aka the "Logjam" issue.

Opera before 19 on Mac OS X allows user-assisted remote attackers to spoof the address bar via vectors involving a drag-and-drop operation.

The intent: URL implementation in Opera before 18 on Android allows attackers to read local files by leveraging an interaction error, as demonstrated by reading stored cookies.

Cross-site scripting (XSS) vulnerability in Opera before 15.00 allows remote attackers to inject arbitrary web script or HTML by leveraging UTF-8 encoding.

Unspecified vulnerability in Opera before 12.15 has unknown impact and attack vectors, related to a "moderately severe issue."