A Cross-site scripting input validation error has been identified in the web interface of the HP Deskjet 6800 printer family.  By sending a string such as <script>alert("found XSS on this page")</script> via a POST request to /refresh_rate.htm the resulting error page will execute the script.  

Verified on Deskjet 6840 firmware version: XF1M131A, but the firmware seems to be generic to the 6800 family, so possibly the entire family is vulnerable.

Vulnerability Timeline: 
3/21/09: Vendor notification via email
3/21/09: Vendor upgrades ticket to "next level of support"
3/31/09: Vendor's "Advanced Support Group" replies: the issue that you are experiencing is due to faulty firmware of the 
printer and as a result the printer needs to be serviced from a HP 
authorized service center.
3/31/09: I Reply asking what firmware version fixes the issue and ask if this vulnerability has been reported previously
3/31/09: Vendor replys: I regret to inform you that there is no specific firmware is available for your printer. As the issue is related to the hardware of the printer, it is beyond the scope of our email support and needs the personal attention of a technician. I would suggest you to get the printer serviced at the nearest HP Authorised service centre. For your convenience I provided below information to locate the nearest HP Authorised service centre.