Opera 10.51 addresses security issues

Opera 10.51 (build 3315) for Windows has been released. This release also addresses a couple of security issues, as well as various stability improvements and other bug fixes.

HTTP Content-Length header can be used to execute arbitrary code
Large values in the HTTP Content-Length header can cause Opera to crash. Certain specific values can cause a memory corruption, which in some cases can allow arbitrary code to be injected and executed. In most cases Opera will just crash. To inject code, additional techniques will have to be employed.

XSLT can be used to retrieve random contents of unrelated documents
XSLT is normally subject to strict controls, preventing documents from separate Web sites from reading the contents of other sites. Certain XSLT constructs can cause Opera to retrieve the wrong contents for the resulting document. These contents will appear randomly from the cached versions of any Web page that has previously been visited, and could contain sensitive information. This information can then be read by the resulting document.