Responses below....
On 7/16/05, Christopher Canova <ccanova@reachone.com> wrote:
I'm doing my best to assist a group with an open source project that
uses amavisd-new and spamassassin called Maia Mailgaurd
(http://www.renaissoft.com/maia/). It's a spam and virus management
system written in Perl and PHP.
Before I get to your specific questions, I'd like to point out the
biggest security issue you are going to face in this system. You are
taking completely untrusted input (emails, including those with
viruses, etc) and displaying it to the user in a web browser. You
will need to be very very careful that you don't allow an attacker to
send a specially crafted email that will inject PHP, Perl, etc code
into your server or inject Javascript, Java, ActiveX, etc into your
user's browser (the later is known as cross-site scripting). This is
not impossible, but can be difficult. Look at all the web
applications that have XSS flaws reported every day on mailing lists.
Remember that the attacker may be one of your users who will know a
lot about how the system is set up and that the application is open
source so the attacker can easily trace the application looking for
flaws, so you need to make sure that the code that processes the
emails is airtight.
We are currently in a discussion about
using the PHP Session ID in the URL and whether to strictly enforce
cookies to avoid session hijacking. The fear is that we could possibly
be passing along the referral information to a spammer willing to
exploit such a vuln. Some of the discussion is related closely to this
mailing list, so I wanted to see what everyone thought about it.
What are the risks to enforcing session handling using cookies? Will it
break functionality for many people? Are the risks of including the SID
in the URL worse than cookies?
In short, you are better off putting the session id in a cookie than
putting it in the URL. You are right that referrer headers are one
way that a URL session id can leak. It may also be logged in proxies
or firewalls.
There is also the problem that users do not expect sensitive
information in the URL. They may send the URL to someone in an IM or
email or even post it on a mailing list or blog, not realizing that it
will give whoever follows the URL access to their account (at least
until the session ID expires).
Finally, I don't like the idea of displaying the session ID on the
screen. It makes the user vulnerable to shoulder surfing and again,
they may send someone or post a screenshot of the application not
realizing that the session ID is there in the URL.
As for breaking functionality for some people, I am not sure how many
people that will affect. I dislike cookies as much as anyone (far too
many sites use them that don't need to), but when you have a web site
that you log in to, they are the best solution. There are some people
that surf the web from a "regular computer" with cookies disabled, but
they are usually advanced users that can handle adding the site to
their exceptions list.
The more common problem with requiring cookies is that some
smartphones and other lightweight browsers may not support them (or
support them properly), so if you anticipate users using these devices
this is an issue you should look into further. You can may want to
consider falling back to using the session ID in the URL if cookies
are not enabled on the browser.
I'd recommend you read up on secure coding practices with Perl and
PHP. There are a lot of resources out there and a lot of issues to
consider, including making sure that an attacker / user cannot guess
another user's session ID.
Good luck.
Chuck
