Content Spoofing is an attack technique used to trick a user into believing that certain content appearing on a web site is legitimate and not from an external source.

Some web pages are served using dynamically built HTML content sources. For example, the source location of a frame could be specified by a URL parameter value; http://foo.example/page?frame_src=
http://foo.example/file.html An attacker may be able to replace the "frame_src" parameter value with "frame_src=http://attacker.example/spoof.html". When the resulting web page is served, the browser location bar visibly remains under the user expected domain (foo.example), but the foreign data (attacker.example) is shrouded by legitimate content. Specially crafted links can be sent to a user via e-mail, instant messages, left on bulletin board postings, or forced upon users by a Cross-site Scripting attack.

If an attacker gets a user to visit a web page designated by their malicious URL, the user will believe he is viewing authentic content from one location when he is not. Users will implicitly trust the spoofed content since the browser location bar displays http://foo.example, when in fact the underlying HTML frame is referencing http://attacker.example. This attack exploits the trust relationship established between the user and the web site.

The technique has been used to create fake web pages including login forms, defacements, false press releases, etc. Example Creating a spoofed press release. Lets say a web site uses dynamically created HTML frames for their press release web pages. A user would visit a link such as: (http://foo.example/pr?pg=
http://foo.example/pr/01012003.html). The resulting web page HTML would be: Code Snippet: The "pr" web application in the example above creates the HTML with a static menu and a dynamically generated FRAME SRC. The "pr_content" frame pulls its source from the URL parameter value of "pg" to display the requested press release content. But what if an attacker altered the normal URL to: http://foo.example/pr?pg=http://attacker.example/spoofed_press_release.html? Without properly sanity checking the "pg" value, the resulting HTML would be: Code Snippet:

To the end user, the "attacker.example" spoofed content appears authentic and delivered from a legitimate source.