I'm serving up locally-generated untrusted content in an iframe from a service worker.
I'm trying to lock down the iframe entirely so that it can only load resources from its srcdoc, which is intercepted by a serviceworker. This means no img etc. from any other domain, but allowing javascript.
To achieve this I'm adding CSP: sandbox allow-scripts; default-src 'self' data:; script-src 'self' 'unsafe-inline'; on all assets served by the service worker, which includes the iframe root.
Loading the iframe root document works fine. But loading an image in the iframe with a relative url, so from the same origin, is not hitting the service worker - but falling through to the parent domain and thus getting a 404. If I remove the sandbox property from the CSP then the image loads, but I lose the security.
Is there a way to get this to work?
I have a demo here: https://ianopolous.github.io/sandbox
I apply the CSP headers in the service worker here:
https://github.com/ianopolous/sandbox/blob/gh-pages/sw.js#L119
Related
If I'm loading another site in an iFrame do the Content Security Policy Headers of that site have any affect on whether the site gets blocked?
e.g. if I open www.google.com in an iFrame is there any interaction between the CSP header settings on my site and the ones on google.com? Or would Google's CSP only affect what they're trying to load in the iFrame.
Of course if google had their own iFrames they'd need CSP headers to allow any 3rd party content to load. But do my CSP headers have any affect on Google's after google.com starts to load? If Google tried to load youtube.com in an iFrame and I didn't include youtube.com in my CSP whitelist would that work?
Sorry if this is a silly question, I'm trying to wrap my head around iFrames. What I'm wondering is if I need to worry about the CSP settings on the third party, especially if I'm nesting iFrames, or if I only need to worry about my CSP policy.
I think what I'm getting at is this: Once I've said "allow this 3rd party site to load" in my CSP headers can that site load whatever it wants based on their CSP headers?
Thanks!
Let's say that you have site A framing site B. Site A must not set a framing policy that denies site B and site B must not set a policy that prevents being framed by A.
Site A can set "frame-src B" to explicitly allow site B to be framed. If frame-src is not set, child-src is used as a fallback, and if that is not set, default-src is used as a fallback. If none of them are restricted, all sites can be framed.
Site B can set "frame-ancestors A" to allow framing by A. This directive has no fallback. If it is not set, any site can frame site B. If it is set, only the sites listed as valid sources can frame it.
Apart for frame-src (child-src, default-src) for the framer and frame-ancestors for the framed, there is no impact on other sites by the CSP, they each control their own sources.
CSP Header directive corresponding to iframes ,
frame-src
frame-ancestors
lets say your site xyz.com and google's site "google.com".
Site xyz.com has its own csp which can controls,
Who can load xyz.com as iframe, decided by frame-ancestors directive
Who can be loaded inside 'xyz.com' as iframe, decided by frame-src directive
same scenario applies for google.com ( whose csp can decide, whom to be loaded as iframe inside its app & whom can load google.com as iframe )
Each html document has its own csp response header, which will not interfere with its host app (parent frame) or its iframes (child frames).
xyz.com 's CSP only decides whom should load it & whom it should load as frame, it cannot control its host frame or child frame ( they are considered as separate entities )
Apart from this another header X-FRAME-OPTIONS is also available with minimal control options to decide whether a site should load as frame or not.
For detailed reference :
CSP - https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy
X-FRAME-OPTIONS - https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options
So I'm trying to avoid using (another) page rule to disable Rocketloader for one of my subdomains, since we can't use a RegEx to select multiple specific subdomains under a single page rule, and only get 3 page rules for free accounts.
According to this page:
https://support.cloudflare.com/hc/en-us/articles/216537517-Using-Content-Security-Policy-CSP-with-Cloudflare
I can just add a header to the domain to allow scripts from CloudFlare:
add_header Content-Security-Policy "script-src 'self' ajax.cloudflare.com;";
I did so in the Nginx config for that subdomain (it's a Chronograph container actually), restarted Nginx, tested to make sure it "took", which it did:
But then when I try to load the domain, it won't load, and the inspector shows this:
Not being super familiar with this, does anyone know where I screwed it up?
where I screwed it up?
First of all, here:
I can just add a header to the domain to allow scripts from CloudFlare:
add_header Content-Security-Policy "script-src 'self' ajax.cloudflare.com;";
I did so in the Nginx config
And secondly, you trusted the report-uri service, but it failed you.
You have had an issue with ajax.cloudflare.com BEFORE adding CSP header into Nginx config (otherwise, why add it). This means that you already have a CSP published via an HTTP header or a meta tag <meta http-equiv= 'Content-Security-Policy'>.
By adding the CSP header to the Nginx configuration, you have added a second policy to the pages.
Multiple CSPs work as sequential filters - all sources must pass through both CSPs to be resolved. The second CSP allows ajax.cloudflare.com host-source, but the first one still prohibits it (that you are observe in the inspector).
You have to figure out where the first CSP is published and to add ajax.cloudflare.com into it, instead of publish second CSP.
No one know what is under the hood of the report-uri and how it will react if two CSP HTTP headers or an HTTP header paired with a meta tag are published simultaneously
Have a look which CSP and how many of them the browser actually gets, the guide is here.
In case of 2 CSP headers you will see something like that:
In case of CSP meta tag you can easily check the by inspecting the HTML code.
I think the report-uri just did not expect such a situation.
Our website is designed based on WordPress tool and published on Azure web service. Our goal is to use google analytic for checking traffic. Due to this fact, the google analysis tag was added in the header part of our page which causes the following error:
Refused to load the script 'https://www.googletagmanager.com/gtag/js?id=??' because it violates the following Content Security Policy directive: "script-src 'self' 'unsafe-eval' 'unsafe-inline' *.msecnd.net *.google.com *.gstatic.com". Note that 'script-src-elem' was not explicitly set, so 'script-src' is used as a fallback.
I understand that violation of the Content Security Policy is the main problem. Therefore, I added meta in the header (Content-Security-Policy:
script-src 'unsafe-inline') but the issue did not disappear. I will appreciate any help.
Since you have got a Content Security Policy (CSP) violation, you already have a first CSP published at the page.
Adding a second CSP via meta tag (or even via second HTTP header) will not solve a problem, because all sources should pass through both CSPs to be allowed.
Therefore you have to add blocked source (https://www.googletagmanager.com) in first CSP into script-src 'self' 'unsafe-eval' 'unsafe-inline' *.msecnd.net *.google.com *.gstatic.com;.
Check if your WP has some installed plugins to manage CSP, or CSP is published in the .htaccess file.
Since you have 'unsafe-eval' 'unsafe-inline' in the script-src, you should not have problems with Google Tag Manager (GTM).
Anyway you can check CSP for your GTM-XXXXXX ID - which additional scripts are loaded by GTM and which tokens are required in you specific case.
I have a web app which I want to display in an iframe in web apps with different domains. Since I have added a content-security-policy header my app refuses to display in iframe. I saw that i need to add frame-ancestors options but all the examples I see are using specific domains. How can I allow it for all domains? Is "frame ancestors *;" enough? Thanks!
Briefly - yes, * allows any sources for iframe except data:.
Pls note that frame-ancestors is not supported in the meta tag <meta http-equiv='Content-Security-Policy' content="..."> (but looks like you use HTTP header to delivery CSP, so this warn not for you).
But if you really wish to allow all frame ancestors - more reliable not specify frame-ancestors directive at all, because for now Mozilla Firefox has some bugs with it.
PS: You did not attach print screen of errors in browser console - may be iframes was block by other reason than CSP?
updated after exposed CSPs details
<html>
parent page issues CSP: default-src 'self';
since frame-src omitted, it fallback to default-src and result be: frame-src 'self'
<iframe src=''></iframe>
</html>
iframe is allowed with the same scheme://host:port as parent page loads.
'self' is tricky in that if parent loaded via HTTP:, iframe via HTTPS: will blocked in CSP2-browsers. CSP3-browsers do upgrade (see para 3) HTTP: to HTTPS:, so all OK.
If parent page issue frame-ancestors * policy, it means you allow to embed it into iframe to any another webpage.
X-Frame-Options HTTP header provide the same functionality, but it's overridden if frame-ancestor is issueed.
frame-ancestor directive does not affects <iframe> embed into page who published this CSP. It affects where it allowed to embed this page.
But <iframe> could publish its own CSP with rule frame-ancestors domain1.com domain2.com to restrict it embedding to other web-pages.
That's how it works. You could play with test of frame-ancestors to clarify details for different <iframe src=/srcdoc=.
Therefore if you embeds iframe from your own domain/subdomains, it's more safe to use:
frame-ancestors 'self';
or if you use subdomains:
frame-ancestors http://example.com https://example.com http://*.example.com https://*.example.com;
There is the Header X-Frame-Options, which is served by the webserver when you want to forbid (or limit) other sites from embedding your page into theirs, using an iframe.
But, is there a Header which tells the browser: "Don't allow any Iframe to be loaded on this page"?
There are, of course, headers which tell the browser which scripts, from which domain, is it allowed to execute, but I want something more generic: "don't allow any iframe, or only iframes from certain origins, to be loaded on this page".
Content-Security-Policy (CSP) can be used to restrict content on pages, including iframes. Specifically, the frame-src directive. If you set the following HTTP header, no iframes will be allowed on your page.
Content-Security-Policy: frame-src 'none'
If you want to only allow iframes from specific origins you could do the following to allow iframes from example.com, and all subdomains:
Content-Security-Policy: frame-src http://*.example.com
You can also set the CSP policy via meta tag.