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XSRF vulnerability in yahoomail..just flaw or security issue?

Although the attack is not severe in nature but can create interruption in user's logged in session.

Yahoomail doesn't use any button to log the user out. It simply provides a link 'Sign-Out' for the logging out the current session.
If the link is encoded in any form (or say disguised in tinyurl) and mailed to any logged in user in yahoomail and if he clicks it,the user who is visiting that page would immediately be logged out.
From the webserver's perspective, there is no difference whatsoever between a real user initiated browser request and the above URL retrieval.

It doesn't carry necessary credentials(e.g. anti XSRF tokens,or any uniquely token generated for the logged in user) with itself to tell the server that it's an extrenal request.Rather it will be using logged in user's credentials to complete the request!

The time discovered it , the other functions of yahoomail was not vulnerable except this "Sign-Out" function.

I had informed them about the vulnerablity but perhaps they didn't consider it an security issue but they now implement no of tokens and identifiers in the 'SignOut' link.

http://in.ard.yahoo.com/SIG=14vivapam/M=590705.12581184.13249026.10993486/D=inmail/S=398320003:HEAD/Y=IN/EXP=1231772641/L=WoCUrMtoEi.FJw6qSWn9mAVS3OIdt0lrP8EADW3f/B=5DsNmspWBvI-/J=1231765441885620/A=4559832/R=5/SIG=143d596d8/*http://login.yahoo.com/config/login?logout=1&.src=ym&.intl=in&.direct=2&.done=http://in.yahoo.com&.last=http://in.mail.yahoo.com/

But still it is not working! I mean the recipient is logged out of his session when he clicks on above link. That should not happen.
I think they are not paying attention to the issue since it is not affecting security of user or website.
In this way Gmail also has the same vulnerability(and might be many others..).
I just pointed out that it's an act of XSRF attack but whether it is an security issue or not, depends on the vendor's perception and how critical is the link that is being exploited.
It's a vulnerability but not Security Issue..I think....
Your Say??

References: http://www.squarefree.com/securitytips/web-developers.html
http://www.codinghorror.com/blog/archives/001171.html

Comments

Chintan Dave said…
Nilesh, I reported similar issues to Google as well. Technically, yes its is a vulnerability, however it makes no significant difference.

Practically speaking, it makes no sense to patch them. The resources spent to patch them are not justified.
January 23, 2009 at 9:01 PM
Nilesh Kumar said…
Yes I agree with you..in a post written to Gmail by me as well..I didn't stick to security impact of the issue rather I discussed about the way it has been implemented. See, underlying fact is that it performs an undesired action using logged in user's authentication.
This is the issue.
And when the same fact is used to exploit other links that may harm a user financially or personally it is called XSRF.
So I said the implementation in itself is wrong.
Anyways, thanks for commenting! :)
February 4, 2009 at 11:45 AM
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