Concept - Protect against CSRF attacks

Note: This vulnerabilility has been fixed.

Problem

See:  MAGNOLIA-5807 - Getting issue details... STATUS

A good resource about the vulnerability is: https://www.owasp.org/index.php/Cross-Site_Request_Forgery_(CSRF)_Prevention_Cheat_Sheet

Referer header example: Referer: http://demoauthor45.magnolia-cms.com/.magnolia/trees/website.html?mgnlCK=1404726339576

Status

We started work on and have a basic implementation of the token method (see above ticket) but are concerned that too many things must be changed to implement it, and that this could cause problems for existing magnolia installations. So we decided to spend some more time researching the "referer-check" approach to see if this is feasible.

Conclusion after 4 hours research

Referer checking should work against known exploits if written correctly. The four downsides i see are:

• It requires that the browser sends the referer header. Some users and companies consider this to be a privacy issue - (and potentially security issue) as the referer header contains information about the browsers history - and could have sensitive information in the form of querystring. So they may currently have browser or company proxy to strip header. Of course we could say its a requirement, but customers could take affront at that (see https://bugs.launchpad.net/launchpad/+bug/560246) Privacy is a hot topic.
  
  • There is a new html5 meta tag to configure if the referer is sent or not.
• I think we can cover the known problems with request checking, but new browser vulnerabilities could come out (flash or other plugins) that create a hole.
• We do have to be careful to implement the referer checking properly.
• More of an image then a technical thing: On the interwebs everyone always recommends using the token approach. Its the accepted, transparent approach. People may be confused or doubtful if you implement a different approach. (See https://www.google.com/webhp?ie=UTF-8#q=csrf+referer+)

Implementation:

Correct Referer check:

• Strictly check the "end" of the hostname. Protect against:
  
  • Open Redirect: http://hackersite.io/?http://demoauthor45.magnolia-cms.com/.magnolia/etc,
  • Tricky Subdomain: http://demoauthor45.magnolia-cms.com.hackersite.io
  • Empty Referer.

Note: There is a vulnerability with a 301 redirect, it forwards its request headers. But this would only be a vulnerability via "xss" - ie if a user of the system somehow put the link on a webpage served by the same magnolia server url. (explicitly: see 301 Redirect Attack: in Notes below.)

Research

OWASP Page: Investigate Referrer Method

https://www.owasp.org/index.php/Cross-Site_Request_Forgery_(CSRF)_Prevention_Cheat_Sheet#Checking_The_Referer_Header

Statement by Statement

• "For example, open redirect vulnerabilities can be used to exploit GET-based requests that are protected with a referer check"
  • This refers to sites with a redirect destination as a parameter like http://www.vulnerable.com/redirect.asp?=http://www.links.com
  • See https://www.owasp.org/index.php/Open_redirect
  • So an attacker could use something like http://hackersite.io/?http://demoauthor45.magnolia-cms.com/.magnolia/etc, and a poorly written referer check might let the request through since the referer will include the domain name.
• "and some organizations or browser tools remove referrer headers as a form of data protection."
  • That individual or organization would have sacrafice their privacy in this case.
• "There are also common implementation mistakes with referer checks. For example if the CSRF attack originates from an HTTPS domain then the referer will be omitted. In this case the lack of a referer should be considered to be an attack when the request is performing a state change."
  • True browsing from an HTTPS page to a HTTP page strips the referer header by design (spec).
  • We simply consider all requests with no referrer to be an attack.

Notes

Privacy

Quote from the HTTP spec:
"
Because the source of a link might be private information or might reveal an otherwise
private information source, it is strongly recommended that the user be able to
select whether or not the Referer field is sent. For example, a browser client could
have a toggle switch for browsing openly/anonymously, which would respectively
enable/disable the sending of Referer and From information.
"

"And in addition to that we also have the fact that referring websites can remove the Referer header with tricks like META refresh"

Django uses a referer check:

https://code.djangoproject.com/ticket/16870

Vitriol of the privacy concious / support requests from hell / this could be us:

https://bugs.launchpad.net/launchpad/+bug/560246

301 Redirect Attack:

4. The victim's browser requests https://attacker.com/badstuff from the attacker's server, and sends Referer: https://launchpad.net/foo in the headers.
5. The attacker's server responds with a 301 Redirect, which redirects the victim's browser to https://bugs.launchpad.net/csrfurl
6. The victim's browser receives the redirect, requests https://bugs.launchpad.net/csrfurl from the launchpad server, and sends Referer:https://launchpad.net/foo with the request.

http://en.wikipedia.org/wiki/HTTP_referer

Most web browsers do not send the referer field when they are instructed to redirect using the "Refresh" field. 

If a website is accessed from a HTTP Secure (HTTPS) connection and a link points to anywhere except another secure location, then the referer field is not sent.^{[9] "Clients SHOULD NOT include a Referer[sic] header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol"}

FYI: Meta tag referrer

http://smerity.com/articles/2013/where_did_all_the_http_referrers_go.html