CSP - style-src 'unsafe-inline' should not be required

[acheronfail]

Expected behavior

react-beautiful-dnd should not depend on the the Content-Security-Policy: style-src 'unsafe-inline' directive.

Actual behavior

react-beautiful-dnd adds errors to the console as the CSS is refused by the CSP rules.

Error messages in console:

Refused to apply inline style because it violates the following Content Security Policy directive: "style-src 'self'". Either the 'unsafe-inline' keyword, a hash ('sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU='), or a nonce ('nonce-...') is required to enable inline execution.
Refused to apply inline style because it violates the following Content Security Policy directive: "style-src 'self'". Either the 'unsafe-inline' keyword, a hash ('sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU='), or a nonce ('nonce-...') is required to enable inline execution.
Refused to apply inline style because it violates the following Content Security Policy directive: "style-src 'self'". Either the 'unsafe-inline' keyword, a hash ('sha256-vGSg8WmFAqZHZBYQl6tE4TGs2MeJ6RK2Dhr+EvafjU0='), or a nonce ('nonce-...') is required to enable inline execution.
Refused to apply inline style because it violates the following Content Security Policy directive: "style-src 'self'". Either the 'unsafe-inline' keyword, a hash ('sha256-b117JbKlS2ulpz6LHY5jTjEXzzX7OvRp9yVkQRfn2ag='), or a nonce ('nonce-...') is required to enable inline execution.

The errors originate from here in react-beautiful-dnd.

Possible Solutions:

1. Add a nonce attribute and make it possible to set the nonce.
   See also: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/script-src#Unsafe_inline_script.
2. Use CSS classes rather than unsafe-inline styles.

Steps to reproduce

1. Use react-beautiful-dnd in a page
2. Open the page with the Content-Security-Policy: style-src 'self' directive set.

(Alternatively, here is a dead-simple create-react-app repository that you can clone and run to see the errors: https://github.com/acheronfail/react-beautiful-dnd-csp).

What version of react-beautiful-dnd are you running?

10.0.3 (Latest at the time of this issue).

[alexreardon]

Fascinating!

[alexreardon]

Would using innerText rather than innerHTML get around the issue?

Alternatively using the Stylesheet api get around this issue?

[acheronfail]

Would using innerText rather than innerHTML get around the issue?

That's a negative.

Alternatively using the Stylesheet api get around this issue?

Also a negative, as quoted here https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/style-src:

Unsafe style expressions

The 'unsafe-eval' source expression controls several style methods that create style declarations from strings. If 'unsafe-eval' isn't specified with the style-src directive, the following methods are blocked and won't have any effect:

CSSStyleSheet.insertRule()
CSSGroupingRule.insertRule()
CSSStyleDeclaration.cssText

---

Basically, the styles must come from a trusted source, and sources can have different levels of trust depending on the CSP rules defined for the webpage.

To work with almost any CSP configuration, you have the following options (see here for a complete list):

• Set/configure a nonce attribute on each element/style
  • Although with this approach you must be careful not to allow dynamically generated content into these styles (that would nullify the effects of CSP here)
• Use CSS classes only and just toggle between classes when needing to set styles
  • This is a win since the content is static and doesn't change, and the user can include/bundle/provide the CSS themselves from a trusted source
• Provide hashes that can be placed in the CSP header
  • This is a quick fix, but needs to be updated each time the styles change (and doesn't work with dynamically generated styles, etc)

[alexreardon]

@acheronfail can you confirm if #1037 removes the warnings?

[acheronfail]

Yep! Can confirm that adding a nonce like #1037 does indeed remove the warnings.

Just to confirm though, is there anyway for these styles to contain user/dynamically generated content (that could allow someone to inject unwanted styles, etc)? 🤔

[alexreardon]

No. The library generates the styles

[m4r71n]

Hi, another solution would be to provide a separate .css file for the preset styles.
Or just an option to disable the preset styles would also help. So we could integrate the preset styles in our own css file.

[alexreardon]

Interesting. We apply different styles at different points in the lifecycle and change their definition. You can read more about it here:

https://medium.com/@alexandereardon/dragging-react-performance-forward-688b30d40a33

[alexreardon]

Dynamically updating styles is a solved problem with styled-components, emotion etc. I would be interested to see how they avoid this issue - so we can use that!

[alexreardon]

Right now we cannot use

Use CSS classes only and just toggle between classes when needing to set styles

As we change the rules on the fly to avoid a re-render to update classes (for performance reasons)

[alexreardon]

We should also add a test to ensure that there are no CSP errors going forward. Perhaps a puppeteer test would be the most appropriate?

[alexreardon]

I think I would be happy to add the nonce given it gets around the issue relatively easily.

Proposed todo:

• Write a cypress test with Content-Security-Policy: style-src 'unsafe-inline'. https://docs.cypress.io/api/commands/visit.html#Arguments to ensure that everything works as expected
• Write a unit test to ensure that the style marshal adds the nonce to the style elements
• Profit

@Zweder are you okay to pick this up?

[alexreardon]

Given that we cannot leverage a class swapping mechanism for performance reasons - lets use this nonce for now.

[Zweder]

I have added unit tests to my PR

But, "Write a cypress test with Content-Security-Policy: style-src 'unsafe-inline'" this doesn't make sense, because cypress is the client not the server which should provide the nonce and the csp-header or meta tag and the cypress tests are running against storybook, that makes it very difficult to set headers.

I'd like to make some real-world tests, but i don't like to hack into storybook, they do a fine job!

@alexreardon any thougts?

[alexreardon]

I just want to ensure that we are actually complying with the CSP. I thought a browser test would enable us to be 100% sure. As you mentioned - using storybook complicates it as we don't have control of the server

The effort to spin up a new micro server and stand alone example might not be worth it

[Zweder]

Having a look at your browser-test-harness.js spinning up a micro server will not be that difficult and i think i can resure a storybook test without breaking changes.

To keep your 'Unopinionated styling' (which i like) possible in a locked down CSP browser, i'm willing to put in the effort to get the tests in place. Btw emotion and jss are doing the same thing to get this working. I's my spare time so i'll need a couple of days.

[Zweder]

I've added a stand alone example and some cypress tests, but there is one thing to mention, cypress strips off the csp header so it doesn't work, but i've added a meta tag in the head with the same policy which also enforces the content-security-policy and that does make it work.

Is it time to profit or am i missing something, comments are welcome

[NikoHelle]

Hi, just asking status of supporting CSP with 'unsafe-inline' rule. There has been a PR open for 8 months that fixes it, but apparently it wont be merged?

Can't use this awesome library because passing a nonce is not supported.

[Zweder]

Sorry, alle Pushed an update, I want it as well Kind regards, Zweder Op di 3 sep. 2019 09:54 schreef NikoHelle <[email protected]>:

…

Hi, just asking status of supporting CSP with 'unsafe-inline' rule. There has been a PR <#1037> open for 8 months that fixes it, but apparently it wont be merged? Can't use this awesome library because passing a nonce is not supported. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1050?email_source=notifications&email_token=ADB7VRZZJKUI6IXEK465PUDQHYJZXA5CNFSM4GPQVIPKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOD5XLASI#issuecomment-527347785>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ADB7VR3CYWJ33KBECRINSFLQHYJZXANCNFSM4GPQVIPA> .

[alexreardon]

This has shipped in #1487. See our new csp guide