I am getting the below error while running the application
Refused to apply inline style because it violates the following Content Security Policy directive: "style-src 'self' https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/ 'sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=' 'sha256-5uIP+HBVRu0WW8ep6d6+YVfhgkl0AcIabZrBS5JJAzs='". Either the 'unsafe-inline' keyword, a hash ('sha256-4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ='), or a nonce ('nonce-...') is required to enable inline execution.
Below is the code currently I am using
const string modernizrHash1 = "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=";
const string modernizrHash2 = "sha256-5uIP+HBVRu0WW8ep6d6+YVfhgkl0AcIabZrBS5JJAzs=";
app.UseCsp(options => options
.DefaultSources(s => s.Self())
.ScriptSources(s => s.Self().CustomSources("https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/"))
.StyleSources(s => s.Self().CustomSources("https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/", modernizrHash1, modernizrHash2))
.FontSources(s => s.Self().CustomSources("https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/fonts/"))
.ImageSources(s => s.Self().CustomSources("data:"))
);
The hash 4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ= is for the CSS word-wrap: break-word; white-space: pre-wrap;, the inline style Chrome automatically applies when you are not serving a HTML document;
Example server response:
Content-Type: text/plain; charset=utf-8
Content-Length: 9
Content-Security-Policy: default-src 'self'
Date: Thu, 04 Nov 2021 11:33:49 GMT
some text
DOM in Chrome
<html><head></head><body><pre style="word-wrap: break-word; white-space: pre-wrap;">some text</pre></body></html>
Console error
Refused to apply inline style because it violates the following Content Security Policy directive: "default-src 'self'"
. Either the 'unsafe-inline' keyword, a hash ('sha256-4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ='), or a nonce ('nonce-...') is required to enable inline execution. Note that hashes do not apply to event handlers, style attributes and javascript: navigations unless the 'unsafe-hashes' keyword is present. Note also that 'style-src' was not explicitly set, so 'default-src' is used as a fallback.```
Adding the hash to default-src or style-src won't help because it is an "inline style" and "hashes do not apply to style attributes".
The best fix is to make sure you serve a proper HTML document with your CSP header, so browsers don't decorate it with their own styling.
You are getting this error because the inline styles (which can be hashed to sha256-4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ=) aren't allowed, as per your Content Security Policy and the error that is returned.
I would recommend two possible steps, either:
Move away from inline styles (as they can be insecure) and will require you to change your CSP each time that the inline styles change.
Add the supplied SHA to the StyleSources for your CSP. But Be aware that this will have to be maintained and updated for each inline style added across all pages in your application.
UPDATE based on comments below answer
Note: There is no issue when i am running it in IE browser, only in the chrome and firefox i am getting the issue
Taking a look at Can I Use shows that IE has only partial support for Content Security Policy, which would explain why you aren't seeing this error in the console. i.e. Internet Explorer doesn't support CSP, so it isn't applying it.
I have fixed the issue by changing the hash keys shown in the browsers console error, I have replaced the console error hash key with my code hash key, but not sure whether this is the permanent solution or not
This is not really a permanent solution. If (and when) your inline styles change, you will have to change the hash in your CSP in order for the styles to be applied again.
Which leads me on to:
Could you please guide me how the hash keys are getting generated and how i can fix this permanently
Looking at the code in your original question:
const string modernizrHash1 = "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=";
const string modernizrHash2 = "sha256-5uIP+HBVRu0WW8ep6d6+YVfhgkl0AcIabZrBS5JJAzs=";
// other things
.StyleSources(s => s.Self().CustomSources("https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/", modernizrHash1, modernizrHash2))
You are telling the browser (via the Content Security Policy that you are generating) that it is only permitted to load styles from:
self (the origin domain of your site)
https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/
and those which match the following hashes:
sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=
sha256-5uIP+HBVRu0WW8ep6d6+YVfhgkl0AcIabZrBS5JJAzs=
You mention that you've also included the hash:
sha256-4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ=
When the browser starts to render the page, it will look at the resources that the page requires in order to render and will compare it to the list in the Content Security Policy. If a resource (inline styles and inline javascript are classed as a resource) is not in the list, then the browser will do a simple SHA-2 of the contents of the resource and compares it to any of the hashes listed in the CSP.
Note: the same thing can be achieved by the use of a nonce
If the resource isn't from an allowed source, or it's hash does not match those listed in the CSP, then the browser will actively refuse it.
Because the SHA-2 algorithm uses the content of the resource to generate the hash, when the contents of it changes the calculated value of the hash will be different.
For example, the inline style here:
<p style="color: red;">hello, world</p>
might hash to F1FF77E5DDBB1AF52EB51C98F725927143221549385937595112128987CF39E4 (which is the hash of "color:red")
whereas the following inline style:
<p style="color: green;">hello, world</p>
might has to 2F262B22412B633D12B27FA9F94A3B0495821CB8341CFF0A88C80E3FED5DC9E8 (which is the hash of "color:green")
As you can see, there is a massive difference in the hashed styles. This is by design (in the algorithm).
To stop alleviate this problem, I would swap the inline styles for a css file describing how the content of the page should be styled. As long as the css file is served from the same origin as your HTML, then the self rule will cover it.
CSP is a pretty complex topic to pick up (but easy to master, once you have learned the basics). I would recommend taking a look at the MDN page for Content Security Policy for more information on how it works and how you can use it to secure your web applications.
Related
From the OWASP's website
https://cheatsheetseries.owasp.org/cheatsheets/Content_Security_Policy_Cheat_Sheet.html:
Send a Content-Security-Policy HTTP response header from your web server.
Content-Security-Policy: ...
Using a header is the preferred way and supports the full CSP feature set. Send it in all HTTP responses, not just the index page.
I don't understand how that could be true as it is possible to set the Content-Security-Policy by using a meta tag in the HTML.
I also don't see how the policy can apply to anything else but HTML pages.
Does anyone have idea why that statement above was made and if it is safe to only send HTTP header Content-Security-Policy for text/html responses?
By the way, the policy is too big and I would like to sent as fewer bytes as possible.
This is still something that’s not formally specified and there ai still some debate on this: https://github.com/w3c/webappsec/issues/520
In general there’s two arguments here:
On the one hand some other file types (XML, PDF, perhaps even SVGs) could benefit from CSP and any resource could become the page by right clicking and opening in a separate tab.
On the other hand CSPs can get quite big and are usually written for HTML pages. So a bit wasteful to send on other resources and most of it won’t be relevant.
The right answer (as suggested by above) is probably to have a reduced, and very strict, CSP for all non-HTML responses.
But I think for most people having it on the HTML only will be good enough and bring most of the benefits of CSP. Then again CSP is an advanced technique so if going as far as that, then why not do it properly?
Using a header is the preferred way and supports the full CSP feature set.
I don't understand how that could be true as it is possible to set the Content-Security-Policy by using a meta tag in the HTML.
Inside the meta tag are not supported the directives:
report-to and report-uri
frame-ansectors
sandox
Also meta tag does not support Content-Security-Policy-Report-Only feature, only the Content-Security-Policy.
All resources that start loading before meta tag in the HTML code are not affected by CSP. Malicious scripts can be injected as first item of the <head> section just before meta tags
The nonce-value is exposed in meta tag therefore can be easely stealing by script and reuse.
Using meta tag you can only set the CSP for HTML pages, but CSP is applied for XSLT in the XML pages, and for some other kinds of content (see below).
Therefore indeed an HTTP header is the preferred way to delivery CSP and using CSP via meta tag does not allow you to use full CSP feature set.
Send it in all HTTP responses, not just the index page.
I also don't see how the policy can apply to anything else but HTML pages.
The specification had in mind a little different - you should send CSP with any response page with HTML content, not only for 200 OK, but even for 404 Not found
403 Access Forbidden, etc.
Because these pages has access to cookie that can be steal in the page not covered by CSP.
CSP is applied not only to HTML pages, but to XSLT in XML-pages, to external javascripts files for workers (in Firefox). Also frame-ancestors directive of CSP HTTP header applies to any content (JPEG/GIF/PNG/PDF/MP4/etc) intended to be embedded into iframe, see the nitty-gritty here.
I want to define a content security policy that allows loading images from any origin by default but restricts this to allow only a specific set of origins in some sections of the website.
In a traditional website that makes a new HTTP request for every navigation, this could be easily done by sending a different Content-Security-Policy HTTP header for the pages that require the stricter policy. But in a single page application, this is of course not possible because navigating to a more restrictive section of the app does not cause a new HTTP request (also I would like to define policies on more dynamic conditions than a URL navigation).
I know that—besides in an HTTP header—CSP policies can also be defined in a meta tag and when multiple CSP policies are defined a request must pass all of them to be permitted. So my first approach to solving the problem was setting a default CSP in a Content-Security-Policy header for the entire page and then dynamically set more restrictive policies by adding a <meta http-equiv="Content-Security-Policy" content="…"> tag to the document's head when required.
And this works just fine for dynamically adding more restrictive policies. The big problem is that removing that meta tag or modifying it does not remove or modify the associated content security policy (tested in Chrome in Firefox). This behavior is defined in the W3C Content Security Policy spec:
Note: Modifications to the content attribute of a meta element after the element has been parsed will be ignored.
So is there any way to dynamically add (and more importantly also remove) a content security policy that does not rely on a HTTP navigation? I would like to avoid setting a restrictive image policy by default and then excepting individual images through hashes or nonces as this would be quite elaborate to implement.
In SPA you can each time to create a new fullscreen iframe and fill it by script. <iframe>, as nested browsing context, can have own CSP meta tag regardless of the parent page.
The parent page will contains only script to manage iframe's content, may be it's possible to use Worker() for this purpose.
Not able to apply css to the asp.net mvc login page. chrome browser says
'Refused to apply inline style because it violates the following Content Security Policy directive: "default-src 'self'". Either the 'unsafe-inline' keyword, a hash ('sha256-PyLHmjCk4/4GwQUxB5Nv2ZOIHPu1XXusXCu09QBy+nc='), or a nonce ('nonce-...') is required to enable inline execution. Note also that 'style-src' was not explicitly set, so 'default-src' is used as a fallback.
enter image description here
Thanks in Advance.
It looks from the error message that you have an inline style, which CSP blocks. You can put that style in your CSS file instead.
You can also use style-src 'self' 'unsafe-inline'; in your content-security-policy declaration, but this is not recommended for security concern.
Check this OWASP explanation for more details.
Summary:
Site at https://localhost:3000 , with Content-Security-Policy value of default-src 'self' 'unsafe-inline' https://localhost:3001/https_index.html contains iframe pointing at https://localhost:3001/index.html. The contents of :3001/index.html contain an . Clicking that link fails: Refused to frame '' because it violates the following Content Security Policy directive.... How can I change my CSP value to prevent this error; to open an new email in user's preferred email client (normal behavior of mailto)? I am using Chrome1
Detail:
Similar but different than this question "mailto link not working within a frame chrome (over https)
"
I think mine is not a duplicate because:
I cannot reproduce that bug, I see a console warning about mixed-content when I try to reproduce their steps:
Mixed Content: The page at 'https://localhost:3001/https_index.html' was loaded over HTTPS, but requested an insecure resource 'mailto:...'. This content should also be served over HTTPS.
My steps are specific; both my page & its iframe src are https, but the page itself is served with a specific and restrictive Content-Security-Policy (CSP):
app.use(csp({
directives: {
defaultSrc: ["'self' 'unsafe-inline' https://localhost:3001/https_index.html"]
}
}));
Also the resulting error I can reproduce is different:
Refused to frame '' because it violates the following Content Security Policy directive: "default-src 'self' https://localhost:3001/https_index.html". Note that 'frame-src' was not explicitly set, so 'default-src' is used as a fallback.
With an image like:
The accepted answers for the original questions will help me work around my CSP-specific issue, that is, if I add a target="_top" to the link, the email client opens without error:
<a target="_top" href="mailto:...">email</a>
A similar fix works for another similar but different issue. However, this may1 sometimes open a new tab
So my question is specifically about the Content-Security-Policy error (see above):
...Refused to frame '' because it violates the following Content Security Policy directive: ...
Notice it says frame ''. The frame is identified as an empty string!
Normally if some resource violates CSP, the URL of the resource is identified; i.e.
Refused to laod the script 'http://evil.com/evil.js'...
And if the CSP-violating URL is identified + provided I can use it; add it to my CSP value for default-src:
`app.use(csp({
directives: {
defaultSrc: ["http://evil.com/evil.js 'self' 'unsafe-inline' https://localhost:3001/https_index.html"]
}
}));`
But can I allow an exception for an href value? Specifically for mailto? I tried wildcards like mailto*, but:
The source list for Content Security Policy directive 'default-src' contains an invalid source: 'mailto*'.
And I wonder if any wildcard would work anyway; does Chrome really consider the href="mailto..." frame as an empty string? I suppose so, since it's not a URL per se; Chrome "wants" to launch an external application (i.e. Outlook) in the context of the iframe; who is bound to the CSP rules of its parent page...
Footnotes:
Chrome displays the above errors in CSP or sandbox cases. Internet Explorer doesn't complain about an iframes href, despite the value of CSP. Internet Explorer also doesn't have the "new tab" problem, despite the value of sandbox. IE 11.1914 will just give message:
The fix of using target="_top" may open a new tab , if you've sandboxed your iframe! (sandbox is different than CSP). I don't like the new tab. Chrome gave me this error...
Unsafe JavaScript attempt to initiate navigation for frame with URL 'http://localhost:3000/' from frame with URL 'https://localhost:3001/index.html'. The frame attempting navigation of the top-level window is sandboxed, but the flag of 'allow-top-navigation' or 'allow-top-navigation-by-user-activation' is not set.
... but opened a new tab, as well as the Outlook email client...
I did what the error suggested; modifying the value of the iframe sandbox attribute:
sandbox="allow-top-navigation allow-same-origin ...", and the mailto link worked (as before), but did not open an excessive new tab. Great!
Stumbled upon this question after encountering the same issue. There is surprisingly little documentation about this after hours of searching.
My first instinct was to do something like you were doing, mailto* or mailto:*.
What finally ended up working was omitting the wildcards, and altering the frame-src directive as such:
frame-src 'self' mailto: tel: *.mydomain.com
tel: links were also were broken in iframes.
This question is about browser behavior as well as protocol specification for linking, importing, including or ajaxing css, js, image and other resources from within html, js or css files.
While testing static files and compressed content delivery in different browsers, I found that some browsers start behaving differently if you move away from conventions. For example, IE6 creates problem if you do not send Content-Disposition: inline; header for all inline css and js etc files, and a recent version of safari does not properly handle pre-compressed gzip CSS files if you use file extension .gz like in main-styles.css.gz.
My question is about the behavior of browsers about Content-Type response header. Since <link>, <script> and <img> tags already reasonably specify the content type of the resource, can this header be safely skipped, or do some browsers require it for some historical reason?
In short, no, it's not required. But it's recommended.
Most browser that I know of will treat <link>, <script>, and <img> properly if they are not sent with headers, but there's no real good reason not to send the headers. Basically, without Content-Type headers, the browser is left to try and guess based on the content.
From RFC2616:
Content-Type specifies the media type of the underlying data.
Content-Encoding may be used to indicate any additional content
codings applied to the data, usually for the purpose of data
compression, that are a property of the requested resource. There is
no default encoding.
Any HTTP/1.1 message containing an entity-body SHOULD include a
Content-Type header field defining the media type of that body. If
and only if the media type is not given by a Content-Type field, the
recipient MAY attempt to guess the media type via inspection of its
content and/or the name extension(s) of the URI used to identify the
resource. If the media type remains unknown, the recipient SHOULD
treat it as type "application/octet-stream".
Regarding the keyword SHOULD, specified in RFC2119:
SHOULD: This word, or the adjective "RECOMMENDED", mean that there
may exist valid reasons in particular circumstances to ignore a
particular item, but the full implications must be understood and
carefully weighed before choosing a different course.
It is required for backward compatibility.
For example: Internet Explorer 10 needs Content-Type:image/svg+xml in order to render any svg file
IE10, IE9 and probably other browsers always need the Content-Type header.
I ran into a problem in java where I tried to post some data via the library chrriis.dj.nativeswing.swtimpl.components.JWebBrowser, which basically displays an internet explorer inside a java program. But the simple php script on the back-end would not parse my post-data. (Used WebBrowserNavigationParameters to set post data while navigating to a certain page) I finally found out that the Content-Type header had to be set for php to properly paste the post-data. (This was not set by default.) Setting it to Content-Type: application/x-www-form-urlencoded and everything worked fine. So, I guess setting Content-Type should allways be done when POSTing data to php.