Bugtraq is Busted, and so is Blogger
Here's a message I've attempted twice to post to Bugtraq, but it appears to have been lost both times. Traffic on Bugtraq has been spotty lately. It talks about a security problem with Blogger's handling of comments:
Having notified Blogger of this twice over the course of a number of months, and not seeing them take any action (beyond saying that they'll look at it) or warn their users, I think it's time to warn people. Under the following conditions, Blogger weblogs are vulnerable to executable code insertion by third parties:
* Comments must be enabled.
* The server must support server-side processing, such as PHP, ASP, SSI, etc. (I'm pretty sure Blogspot-hosted blogs are NOT vulnerable).
* The Archive Filename (in the Settings/Archiving tab) must have an extension which triggers server-side processing, such as .php, .asp, .shtml, etc. Depending on one's server configuration, files with extensions like .html and .htm may also be server-side-processed--no particular extension is necessarily safe.
* It may be necessary to have individual post pages enabled (also in the Settings/Archiving tab)--I haven't checked where the comments go with that setting off.
Under these circumstances, an attacker may inject executable code into the archive page by posting a comment to the weblog because, while Blogger automatically strips most HTML from comments, they do not strip processing instructions. Blogger should be stripping out EVERYTHING between a "<" and the next ">" unless it is one of the allowed HTML tags, or should be stripping all unapproved HTML and converting any remaining "<" characters that aren't part of approved HTML to <.