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Mozilla Foundation Security Advisory 2005-22
Title: Download dialog spoofing using Content-Disposition header
Reporter: Andreas Sandblad (Secunia)
Products: Firefox, Mozilla Suite
Fixed in: Firefox 1.0.1
Mozilla Suite 1.7.5
Andreas Sandblad of Secunia Research demonstrated a method to spoof the download dialog for saving files by supplying a Content-Disposition header with a different extension than the extension visible in the link and download dialog. Users could be tricked into downloading a safe-looking file such as a JPEG image and have it actually be saved with an executable extension.
Windows hides file extensions by default. If the user did not notice the incorrect icon they might at some later time double-click on the saved file and execute it instead of having it open in the expected media application.
Use caution when downloading files from an untrusted site, un-hide file extensions on windows.