I think you are definitely on the right track here, though I
unfortunately haven't had time to look at your code (thus, I'm just
going by your description).
Due to frequent vulnerabilities found in Internet Explorer's cookie
handling (versions 4.0 - 6.0 allow anyone to view cookies from any
domain, regardless of the cookie's characteristics), cookies should be
considered public by any system attempting to be secure. Meaning, if
both your key that you describe as well as the session ID are stored in
cookies, a compromise of both these cookies opens you up to a
presentation attack. This does not require the attacker to sniff the
HTTP traffic in any way, so even the use of another security method such
as SSL does not prevent this type of attack.
Instead, you should consider some sort of combination approach, where
you utilize both URL variables and cookies. URL variables are quite
exposed (and can be revealed with the Referer HTTP header), so you want
to make the exposure of this by itself useless to an attacker. At the
same time, you want a cookie compromise to not compromise your entire
mechanism. By requiring both types of attacks, you at least make a
compromise more difficult and therefore slightly strengthen what you've
already got.
Hope that helps. Happy hacking.
Chris
mar tin wrote:
Dear all:
Until I read the article PHP Session security
(http://www.webkreator.com/php/configuration/php-session-security.html)
I haven't noticed how insecure PHP Sessions are.
Basically there're 2 problems:
*) It's possible to hijack a session if you know the
SID (session id)
1) If you're on a shared server (cheap webhosting)
other users can get the SIDs by doing ls /tmp/sess_*
(/tmp/ is defined on session.save_path on the config
file, so it may be different).
2) When a user clicks on an external link, the
browser sends the REFERER url and sometimes it
contains the SID (if session.use_trans_sid is enabled)
PHP offers a security measure: with
session.referer_check it will reject SIDs comming from
other referers, but the referer url can be easily
forged.
*) Users can read session data from the session files,
which are owned by the server process (every user
which has an account on the webserver can read server
owned files)
(If you're intrested in the subject I would recommend
to read full the article:
http://www.webkreator.com/php/configuration/php-session-security.html)
I have developed some functions to avoid this
problems. They replace the standard session functions
(using session_set_save_handler), so you only have to
include the file at the beggining of your script and
(afaik) you're safe :)
This is the idea:
Apart from the session cookie, I set another one (with
the same name and the string '_sec' appended). On this
cookie I set a random KEY.
The name of the file which contains the session data
is the md5 hash of the SID and the KEY together. This
turns impossible to guess the session id by looking at
the filenames.
To hide the data inside the file, the serialized
string is crypted using the KEY as password, so nobody
can see the content of your user's sessions.
You can find the code here:
http://www.n3rds.com.ar/files/docs/php_sessions/sess_handler.txt
Im looking for suggestions to make it 100% compatible
with the standard session functions, and I would like
to hear some thougts about the idea
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