I'm going to try and throw another issue into this discussion now too: denial of service. We have discussed it for attacking remote servers, but not for the client viewing the image. It's something else that I spotted while I was playing around with this issue just now. If you have images that include a mailto:meat_private source, then the default handler for mailto: links is opened up. Be that Outlook, Netscape Composer, Eudora, or whatever else you care to use. So if someone embedded 100 (arbitrary figure) mailto: images in a page, then this would do a lot of harm to the user's computer. At best, it would get very busy for a few minutes creating new emails, and would be a pain to clear up. At worst, it could bring the whole system crashing down. So there's something else that needs to be checked in webmail clients in incoming mail, or user submitted content on forums, guestbooks, etc. Blocking mailto: in image tags seems like the best solution for us at vBulletin, so that is probably what we will do. In most general cases, only allowing mailto: in <a href=... tags seems like the best solution, or at least not allowing it in images, iframes, embed, object, javascript, etc, etc. I have a feeling that accessing news: or nntp:// might have a similar undesirable effect, but I have not tested this. Finally, another problem that we had to address a while ago in vBulletin was the use of the about: 'handler' in Internet Explorer. Try viewing this URL from your faviourite version of IE (tested on 6.0 beta) about:<head><title>Hi</title></head><body><p>Hello</p></body> This allows anyone to insert their very own HTML, unchecked for nasties, javascript, or anything else, directly into the client's browser. Note that it may need to be 'url encoded' according to RFC1738. This will work for an <a tag, and I guess that if would probably work for an iframe. In vBulletin, we test against that by adding a space between about and the colon, which effectively disables any problems. A few that I did test within images in Internet Explorer 6.0, but did not come out with anything useful, are: http://wwp.icq.com/scripts/search.dll?to=42892594 aim:goim?screenname=jhpercival&message=Hi.+Are+you+there? telnet://loggerat_private Anyway, a few more things to discuss and chew over there! Regards, John Percival Product Manager, vBulletin http://www.vbulletin.com/ mailto:johnat_private "vBulletin: Community Instantly"
This archive was generated by hypermail 2b30 : Fri Jun 22 2001 - 14:16:36 PDT