Saqib,
No offense, but that's a bad solution. You should never rely on
non-validated header content. If you don't really care very much, but
kinda-sorta want people to not leech, then that's one thing, but if the
application "requires anti-leeching", you need to do a lot more than
check the referrer header. Some ideas could be:
* short life cookie (set it in the surrounding html, check when
loading the image or whatever)
* check for a active session (authenticate)
* funnel all static content through a servlet or something,
http://server/get_file?id=abcdefg
Regards,
Mike
Michael Scovetta
Computer Associates
Senior Application Developer
-----Original Message-----
From: Saqib Ali [mailto:docbook.xml@gmail.com]
Sent: Wednesday, March 02, 2005 12:23 AM
To: RSnake
Cc: Kevin Conaway; webappsec@securityfocus.com
Subject: Re: Preventing direct URL access in a J2EE environment
well for most applications that require anti-leeching, just deny any
HTTP request which has the HTTP_REFERER set to blank.
In Peace,
Saqib Ali
http://validate.sf.net
On Tue, 1 Mar 2005 14:34:30 -0800 (PST), RSnake <rsnake@shocking.com>
wrote:
Referers are also not availible in some security settings.
Zonelabs Zone Alarm Pro, and both Norton Internet Security and
Norton Personal Firewall all drop the referring URL. Forget
spoofable, sometimes it's just not there at all.
See this for details from Symantec:
http://service1.symantec.com/SUPPORT/nip.nsf/46f26a2d6dafb0a788256bc7005
c3fa3/b9b47ad7eddd343b88256c6b006a85a8?OpenDocument&src=bar_sch_nam
There are a number of tricks you can use to get more
information
from the user's machine, but Referring URL isn't reliable.
Not
to mention it can also be non-existant via meta refreshing.
On Tue, 1 Mar 2005, Saqib Ali wrote:
It is a commonly used technique called anti-leeching or
anti-leaching .
Search for "anti leeching php" or "anti leeching jsp" on Google. You
will find many resources.
You can control the path that a user takes by checking for the
HTTP_REFERER . But this is not a fail-proof technique, because the
HTTP_REFERER can alwasy be spoofed.
In Peace,
Saqib Ali
http://validate.sf.net
On Tue, 1 Mar 2005 10:19:37 -0500, Kevin Conaway
<kevin.conaway@gmail.com> wrote:
For our application, we would like to prevent users from requesting
application resources directly. E.g. browsing to
http://localhost/app/method.do?id=5&type=3 instead of actually
clicking on a link that the application provides.
We would like to do this without a major impact on our code. I was
thinking of using the following scenario:
- Currently we have tag libraries that help build all our URLS.
These
tag libraries would be modified to include a strong cryptographic
token that is unique to each URL/User combination. - The token/URL
combination would be stored in the application context for a
pre-determined amount of time.
- Next, we would use a Servlet filter to intercept the URL. First,
deny URLS requested without tokens. If a token is passed, verify
that
matches the token stored in the application context for the
requested
URL.
For the token, I was considering using SecureRandom to generate a
random number and compute a hash of the random number and the URI
being requested. This would be stored along with with URI and the
user Id.
Could anyone point out any pitfalls I need to be aware of, or if
I'm
going about things the wrong way?
Thanks
Kevin
--
In Peace,
Saqib Ali
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--
In Peace,
Saqib Ali
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