Opera before 10.00 trusts root X.509 certificates signed with the MD2 algorithm, which makes it easier for man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted server certificate.

Opera before 10.00 does not properly handle a (1) '\0' character or (2) invalid wildcard character in a domain name in the subject's Common Name (CN) field of an X.509 certificate, which allows man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority.

Opera before 10.00 does not properly display all characters in Internationalized Domain Names (IDN) in the address bar, which allows remote attackers to spoof URLs and conduct phishing attacks, related to Unicode and Punycode.

Opera before 10.00 on Linux, Solaris, and FreeBSD does not properly implement the "INPUT TYPE=file" functionality, which allows remote attackers to trick a user into uploading an unintended file via vectors involving a "dropped file."

Opera before 10.00, when a collapsed address bar is used, does not properly update the domain name from the previously visited site to the currently visited site, which might allow remote attackers to spoof URLs.

Opera 9.52 and earlier, and 10.00 Beta 3 Build 1699, does not properly block data: URIs in Location headers in HTTP responses, which allows remote attackers to conduct cross-site scripting (XSS) attacks via vectors related to (1) injecting a Location header that contains JavaScript sequences in a data:text/html URI or (2) entering a data:text/html URI with JavaScript sequences when specifying the content of a Location header. NOTE: the JavaScript executes outside of the context of the HTTP site.

Opera 9.52 and earlier allows remote attackers to cause a denial of service (CPU and memory consumption, and application hang) via a long Unicode string argument to the write method, a related issue to CVE-2009-2479.

Opera 9.52 and earlier does not block javascript: URIs in Refresh headers in HTTP responses, which allows remote attackers to conduct cross-site scripting (XSS) attacks via vectors related to (1) injecting a Refresh header or (2) specifying the content of a Refresh header, a related issue to CVE-2009-1312. NOTE: it was later reported that 10.00 Beta 3 Build 1699 is also affected.

Opera, possibly before 9.25, uses the HTTP Host header to determine the context of a document provided in a (1) 4xx or (2) 5xx CONNECT response from a proxy server, which allows man-in-the-middle attackers to execute arbitrary web script by modifying this CONNECT response, aka an "SSL tampering" attack.

Opera, possibly before 9.25, processes a 3xx HTTP CONNECT response before a successful SSL handshake, which allows man-in-the-middle attackers to execute arbitrary web script, in an https site's context, by modifying this CONNECT response to specify a 302 redirect to an arbitrary https web site.