Hi, Even if site is using 'self' CSP policy for all types of resources, attacker can still inject <base> tag and CSP can not stop it. e.g., On testing environment: http://www.mobilefuxx.de/csp/xsstest/test_unsafe.php , you may set the following CSP header as an example: default-src 'self'; and in the allowed injection area, inject: <BASE HREF="http://www.google.com/logos/"> <img src="classicplus.png"> Now click "Submit Attack" button ... nothing happens but behind the scene chrome has changed the base URL. You can see the new URL by clicking the "Submit Attack" button again and the URL now you have is: http://www.google.com/csp/xsstest/test_unsafe.php I think or I would like to suggest that CSP 1.1 would have also base-src 'self' directive in order to stop base tag injection. At the same time I would also like to point out few posts related to base tag and how attacker can use this to ex-filtrate information. Thanks! http://lcamtuf.coredump.cx/postxss/ http://www.thespanner.co.uk/2011/12/21/html-scriptless-attacks/ http://avuko.net/ Thanks!
That's a good idea. Would you be willing to email this information to the public-webappsec mailing list? That's the appropriate forum for proposing features for CSP 1.1. Thanks!
Hi Adam, Thanks for information. I will do that. Thanks! Best, (In reply to comment #1) > That's a good idea. Would you be willing to email this information to the public-webappsec mailing list? That's the appropriate forum for proposing features for CSP 1.1. > > Thanks!
> (In reply to comment #1) > > That's a good idea. Would you be willing to email this information to the public-webappsec mailing list? That's the appropriate forum for proposing features for CSP 1.1. > > > > Thanks! I've just put together a test at https://mkw.st/p/mixed/base.html and can't reproduce your result, Ashar. Could you put up a sample that exhibits the problem (or did I screw up my test?)? Thanks!
Hi Mike, I have just tested this again and it works in Chrome Stable version but in Canary it does not work. In Chrome Stable the URL http://www.mobilefuxx.de/csp/xsstest/test_unsafe.php becomes http://www.google.com/csp/xsstest/test_unsafe.php Steps to Reproduce ----------------- 1) In Chrome Stable open: http://www.mobilefuxx.de/csp/xsstest/test_unsafe.php Set header 'self' and in the text area inject: <BASE HREF="http://www.google.com/logos/"> <img src="classicplus.png"> Click "Submit Attack" button. Behind the scene in Chrome Stable the base URL which is mobilefuxx has been changed to google. You can see this by clicking on the button(Submit Attack) again. I hope it helps. Thanks! (In reply to comment #3) > > (In reply to comment #1) > > > That's a good idea. Would you be willing to email this information to the public-webappsec mailing list? That's the appropriate forum for proposing features for CSP 1.1. > > > > > > Thanks! > > I've just put together a test at https://mkw.st/p/mixed/base.html and can't reproduce your result, Ashar. Could you put up a sample that exhibits the problem (or did I screw up my test?)? > > Thanks!
Great. Looks like this is fixed in trunk, then.