Skip to main content

Disclosure of Anti-CSRF Token in URL

Is it a problem? I think no, as long as the token is Per Page, One-time use token.
Actually in one of the application, we had recommended to implement anti-CSRF tokens. When the application came back to us for verification process, we found that the application was implementing some sort of CSRF tokens, which were:
1) Going in GET request ie. were being added to URL.
2) Were being generated per page.
3) Were one-time tokens.

The only concern was the token in GET request. I mean it can be said that it is certainly not a best practice but the potential risk is very minimal. In a scenario where it can be exploited depends on following constraints:
1. The victim should be logged into the application (obvious).
2. The CSRF token must be transmitted in a GET request.
3. The attacker must be able to capture the token or from a repository (log files, browser cache etc).
4. The attacker needs to trick the victim to click on the crafted link.
5. The victim's session that holds the exposed token should be still valid ie, it is not timed-put,invalidated,logout, expire etc.

The 5th point is major hurdle in executing CSRF in this scenario. In our case, although the application was exposing tokens in URL but it was generating them per page/request and one-time only. So even if you have got the token for the current GET request there is minimal chance that you can execute it as next time the user will be browsing the same page with some other unique token.Even if the CSRF token is exposed and the attacker is somehow able to figure out the associated user, the token is only valid for the lifetime of one request.
Also I had consulted with few security experts and one of them

Is the csrf token per/page or one-time use for each request? The difference being if a client accesses the same page multiple times is the token changed? If not, then GET may be an issue.

I have seen the following csrf token implementation strategies:

1) Per Session token
2) Per Page token
3) Per Page, One-time use token

#3 is the most secure as it prevents token reuse.

--
Ryan

So our application was changing the request and was one-time, so it was good enough!
We might have suggested them to put it into PUT request but again they had to do again some levels of coding. And as far as the things are secure enough in GET why to go for PUT. I am not supporting tokens in GET but trying to make a balance between security and client.

Comments

Popular posts from this blog

SQL Injection in search field

Earlier I had written about performing SQL injection in search field and how to do a DoS attack and privilege escalation using 'Like' operators. Now another SQLi exploitation I came across recently. That too in the search field. This becomes important as lots of people don't pay much attention on the search forms/ fields in the application. My aim is to show that a search form can also be exploited with SQL Injection. The following queries are based on a real world exploitation. The steps and data are for just illustration purpose only. Suppose, the search form provides the details of users who have accessed the application some time and their login time details etc, we just need to provide their name in the search box provided. All the data were being going as Post request. So, to just fingerprint the database, I provide, 'nil'+'esh' in the search field and it successfully gives me the results. That means the database behind the application is concatenat…

File Upload through Null Byte Injection

Sometimes, during file upload we come across situation wherein there would be check on the file extension at the client side as well as server side too. If the application does allow only .jpeg extension to be uploaded, the client side java script checks for the extension of the file before passing the request. We all know that how easily this can be defeated.
Some applications, checks for the extension at the server side also. That's not easy to bypass. However there are some ways with which it still can be bypassed. Most of server side scripts are written in high level languages such as Php, Java etc who still use some C/C++ libraries to read the file name and contents. That leads to the problem. In C/C++ a line ends with /00 or which is called Null Byte. So whenever the interpreter sees a null byte at the end of the a string, it stops reading thinking it has reached at the end of the string.
This can be used for the bypass. It works for many servers, specially php servers. Th…

Insecure protocols

Some basic insecure protocols and risk associated with them: