Thursday, May 22, 2014

Can't Open Files/Send Attachments in Firefox? Check Your DEP Settings (XP)

As support for Windows XP officially ended on April 8th, you kind of need to rely on yourself now to ensure that your machines is still secure. Like many people, I've got an old computer that still gets some occassional use - and therefore needs as much security as it can get. But oftentimes, safety doesn't go hand in hand with compatibility.

After looking around on the Internet, I decided to enable DEP (Data Execution Protection), an anti-exploit mechanism, for all programs. This method has been encouraged by sites such as Tom's Hardware and Pc Mag, and after weighting the pros and cons decided to enable the feature on my computer. Simply right-click on My Computer, select Properties, Advanced, Performance, and Data Execution Prevention.The picture below shows it turned off - click the appropiate box to enable it for all programs and services.

Windows XP DEP Dialog
DEP Settings Dialog

Everything worked fine, and I didn't really give that setting much thought. That was before I simply sent a email with Firefox, and found out that I couldn't open the "attachments" dialog in Outlook (Hotmail). Checks with Gmail revealed the same thing, and File → Open on the menu bar didn't work as well. Basically, anything that required the Explorer dialog (including changing the download location) mysteriously failed.

What's the fix? Well, DEP is the culprit. By believing that Firefox's attempt to access Windows Explorer was an attack, it silently blocked it without a hitch. The good news is that this problem can be averted, albeit with a slight decrease in security level. Simply exempt explorer from DEP protection by adding explorer.exe into the box below. Apply, restart, and everything should work fine once again.

Windows XP DEP Dialog
Setting up an exception for Windows Explorer.
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