On 03/18/2010 05:57 AM, Caleb James DeLisle wrote: > This message seems to have disappeared, resending... > > Alex Busenius wrote: >> On 03/16/2010 10:23 AM, Caleb James DeLisle wrote: >>> >>> Marius Dumitru Florea wrote: >>>> Hi Caleb, >>>> >>>> Caleb James DeLisle wrote: >>>>> I don't want this proposal to die because of unnecessary noise which I >>>>> introduced, >>>>> I have thought about it and I am in agreement with the general idea of >>>>> sending the user a hash which >>>>> must be returned with the post in order for the data to be saved. >>>>> >>>>> I don't like adding code to xwiki-core so I suggest this be made into a >>>>> component. >>>>> We would need 2 functions: >>>>> String getToken() >>>>> boolean isTokenValid(String token) >>>>> >>>>> getToken uses org.xwiki.bridge.DocumentAccessBridge.getCurrentUser() to >>>>> get the user who called it >>>>> and the user name is stored in a HashMap of <String, String> with a >>>>> random string of text. >>>>> >>>>> If getToken finds a token already in the map, it returns that token (so >>>>> it may be called multiple times >>>>> in the generation of a page) >>>> So the token is the same for consecutive (GET) requests coming from the >>>> same user? >>>> >>>>> isTokenValid checks the current user against the token then removes the >>>>> entry from the HashMap so the token >>>>> may not be reused. >>>> What happens if the user opens in edit mode two different pages? Isn't >>>> the second save invalidated by the first save? >>> Good point I missed. I would have to have a script to disable such an >>> onerous 'feature' :) >>> I guess it will only work if a single number is valid basically forever. I >>> wish components had access to the >>> Request, Response and Session so it could expire on logout. >> >> What if this map would store a mapping (user + url) -> token, > URL sounds like a good idea, what are the chances that a user will be editing > the same page in 2 windows? Even if > they are, editing the same page will cause past changes to be lost. Perhaps > if the token fails they should get a > page with a warning message and an opportunity to save anyway.
Editing the same page in two windows is probably not common, but the behavior would change. Currently, both saves work and _both_ are recorded in the history in the order they were saved. With the tokens the editor that was opened first would get an access denied on save, and the one opened last would work. I'm not sure how we can go back to editor and refresh only the token but leave the modified text. And the natural reaction of a user would probably be to hit the back button in browser, which would restore the editor page with the invalid token. > We can compare the URL to the referrer header which makes life easy (we would > need access to the request but I > think this is coming soon.) > True, once we have access to the request we could easily add referrer header checking. >> or (user + >> reason) -> token, where "reason" would be some description of the >> intended change like "edit:Main.Test" or "rights:SomeUser+comment-edit"? > This idea sounds like it would require a lot of extra infrastructure, maybe I > am not seeing it right. No, the "reason" would contain only the important part of the things that are currently usually in the URL, like document name and action. >From the viewpoint of token component the exact content doesn't matter, it should just contain enough information to differentiate editing of different things. The reason for this idea is that we would need to give the same URL to both getToken and isTokenValid as an argument, but those methods are usually called from totally different places. So I think it is easier to give the (somewhat simplified) reason instead of trying to come up with the same URL after several redirects. For example, URLS for editing and deleting a page clearly differ in the action part (/delete/Main/WebHome vs. /save/Main/Webhome), but most administrative tasks go to /admin/XWiki/XWikiPreferences, are redirected to saverights.vm and only differ in the query part of the URL. Pages can also be edited over /preview/... with correct parameters. Changing access rights sometimes use /save/... as URL, etc. WDYT? Alex >> >> getToken would return different tokens for different pages/"reasons" and >> isTokenValid would need to provide the same url/"reason" for check to >> succeed. >> >> >>> Caleb >>> >>>> Thanks, >>>> Marius >>>> >>>>> If a configuration parameter is specified to disable the component, >>>>> getToken returns "" and isTokenValid >>>>> returns true. >>>>> >>>>> WDYT? >>>>> >>>>> Caleb >>>>> >>>>> >>>>> Caleb James DeLisle wrote: >>>>>> Sergiu Dumitriu wrote: >>>>>>> On 03/10/2010 07:44 PM, Caleb James DeLisle wrote: >>>>>>>> Take a look at the "sammy is my hero" worm, myspace sent a hash to the >>>>>>>> user like the one you propose, >>>>>>>> the worm made the required get request to get the hash, then made the >>>>>>>> post along with the hash. >>>>>>>> What prevents javascript from opening the page with the hash in an >>>>>>>> iframe and then reading in the iframe >>>>>>>> to get the hash, then creating a form with the required data and >>>>>>>> posting it to the save action? >>>>>>>> >>>>>>>> If we were to combine a requirement for post requests with checking of >>>>>>>> the referrer header, then we >>>>>>>> would block links, forms and javascript based attacks leaving only an >>>>>>>> attack through older versions >>>>>>>> of flash which support referrer forgery and at this point the >>>>>>>> difficulty of the attack becomes such that >>>>>>>> we need to consider a wider array of attack vectors. >>>>>>> Sammy also required that XSS is enabled. >>>>>>> >>>>>>> Protecting from attacks originating in the wiki is kind of impossible >>>>>>> at >>>>>>> the moment, since JS can be inserted anywhere, and there's no (nice) >>>>>>> way >>>>>>> to prevent attacks from JS inside the application. As long as JS can be >>>>>>> inserted, an attacker can do all the steps that the client would do to >>>>>>> perform an action. >>>>>>> >>>>>>> The secret token works as a prevention mechanism when the attack comes >>>>>>> from another site because the browser security model prevents the >>>>>>> attack >>>>>>> code to read the form. >>>>>> I just did a few tests on iframes and I was wrong, they do have good >>>>>> same origin policy. >>>>>> >>>>>> Caleb >>>>>> >>>>>>>> Caleb >>>>>>>> >>>>>>>> >>>>>>>> Alex Busenius wrote: >>>>>>>>> Unfortunately, using POST requests instead of GET requests is not >>>>>>>>> enough. It will not prevent attacks that use forms and/or JavaScript >>>>>>>>> to >>>>>>>>> generate POST requests. >>>>>>>>> >>>>>>>>> Alex >>>>>>>>> >>>>>>>>> >>>>>>>>> On 03/09/2010 02:48 PM, Caleb James DeLisle wrote: >>>>>>>>>> I had thought about proposing this myself but decided against it >>>>>>>>>> because it seems >>>>>>>>>> to me like a workaround for problems which can be solved in other >>>>>>>>>> ways. >>>>>>>>>> >>>>>>>>>> Suppose we were to add a check to the actions which alter data which >>>>>>>>>> made sure the request method >>>>>>>>>> was 'post' and made it configurable in one of the configuration >>>>>>>>>> files? We would have >>>>>>>>>> to look over the default skins for incorrect links and leave the >>>>>>>>>> configuration >>>>>>>>>> option off by default for backward compatibility at least until the >>>>>>>>>> next major version >>>>>>>>>> but we could provide wiki operators the ability to prevent CSRF. >>>>>>>>>> >>>>>>>>>> Caleb >>>>>>>>>> >>>>>>>>> _______________________________________________ >>>>>>>>> devs mailing list >>>>>>>>> [email protected] >>>>>>>>> http://lists.xwiki.org/mailman/listinfo/devs >>>>>>>>> _______________________________________________ devs mailing list [email protected] http://lists.xwiki.org/mailman/listinfo/devs
