Microsoft Internet Explorer 5.0 is susceptible to a very simple Denial of Service attack involving cookies. Default security settings open this hole, and there is currently no fix. Other problems with the way that MSIE 5 handles cookies are also discussed.
001ad23591344f3f96704123a800a5f37cda7ba2dc463b34b93763eb07bc7214
Date: Wed, 24 Mar 1999 01:16:36 -0400
From: Claudio Valderrama C. <cvalde@USA.NET>
To: NTBUGTRAQ@LISTSERV.NTBUGTRAQ.COM
Subject: MSIE 5
Hello.
I hope this will avoid headaches to system administrators:
- MSIE 5, when installed, changes silently the setting for the cookies to
"Accept always" no matter how did you have it in IE4 before. This is because
M$ changed cookies configuration from the "Advanced" to the "Security" tab.
- MSIE 5 cannot be used with cookies set to "Prompt before accepting" when
visiting sites that send many cookies: after choosing NO (reject) to each
cookie more than three or four times, MSIE will crash with a memory error. I
was able to repeat the crash in some NT systems: a generic computer, a Dell
computer, etc. Look for a cookie intensive site, like www.celebsite.com and
see for yourself. I never saw this to happen on MSIE 4 SP1.
- MSIE 5 includes a new "Allow per session cookies" setting, that's enabled
by default. I think session cookies are less dangerous than persistent
cookies.
- By default, AutoComplete will offer to save passwords used on sites you
visit. Be careful, because while you are typing to fill in a form, if you
continue typing, you may press the "Y" as part of your text just in the
moment the popup window ask you to save the pw and you won't notice what
happened.
- MSIE 5 created a service called "COM+ Event System" no matter I downloaded
first all files and later I installed custom. What is this service intended
for? I remember that after installing RDS (part of M$'UDA), I discovered
some RDS objects where opened to anyone that knew how to connect to them. I
hope this time, the new service won't open a new security breach.
Note that all computers had NT 4 SP4 installed and it's the US version.
C.
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Date: Wed, 24 Mar 1999 09:47:58 -0700
From: Mark <mark@NTSHOP.NET>
To: NTBUGTRAQ@LISTSERV.NTBUGTRAQ.COM
Subject: Re: MSIE 5
Late last week, I had made MS aware of the cookie setting configuration
being reset during installation, in addition to another oddity I was
observing:
Apparently, if you accept one cookie from a site, all others are also
accepted without prompting, regardless of the cookie setting.
Also, if you have an old cookie from some site on your disk, and you revisit
that same site with the cookie setting adjusted to prompt for acceptance, no
prompt is given, and the cookie is automatically written to disk anyway.
Ouch.
this was observed on NT Workstation 4.0 with SP4, where I had installed IE5
as an upgrade to IE 4.01.xxxx
for the record, i've never seen my installation of IE5 crash due to not
accepting cookies (or any other reason for that matter.) i tried this at
www.enanet.org, where that sites sends a vertiable truckload of cookies at
you. maybe they should rename the site after the keebler elves ;-]
mark
> I hope this will avoid headaches to system administrators:
> - MSIE 5, when installed, changes silently the setting for the cookies to
> "Accept always" no matter how did you have it in IE4 before. This
> is because
> M$ changed cookies configuration from the "Advanced" to the
> "Security" tab.
> - MSIE 5 cannot be used with cookies set to "Prompt before accepting" when
> visiting sites that send many cookies: after choosing NO (reject) to each
> cookie more than three or four times, MSIE will crash with a
> memory error. I
> was able to repeat the crash in some NT systems: a generic
> computer, a Dell
> computer, etc. Look for a cookie intensive site, like
> www.celebsite.com and
> see for yourself. I never saw this to happen on MSIE 4 SP1.