Bug 277852 – CSP throws error when font referenced, not when loaded

• Component: WebCore Misc.
• Status: RESOLVED WONTFIX

[Robin Whittleton]

Created attachment 472095 [details]
No CSP error is expected from the test page; uncomment the last paragrpah to force an expected CSP error

I have a CSS @font-face definition, which includes a unicode-range that doesn’t match any characters in the page. The page has a CSP that blocks all font-src loading. On page load, the browser throws a CSP exception error, even though the font file isn’t (yet) needed, and hasn’t loaded.

My understanding from https://www.w3.org/TR/CSP3/#framework-violation is that there needs to be a request association with a violation, but in this case there hasn’t been one, so a violation shouldn’t be issued (at least until the page changes to violate the CSP).

Firefox works in the way I’d expect: no CSP exception is issued until a character is added to the page that matches the @font-face’s unicode-range. Blink acts in the same was as WebKit.

[Robin Whittleton]

So, I honestly have no idea why I thought Firefox didn’t throw an error, because I’m now seeing it in the testcase I attached 🤦‍♂️

Given that all browsers agree on this, I guess this might be one to close, even if the behaviour doesn’t feel correct according to the spec.

[Radar WebKit Bug Importer]

<rdar://problem/134034960>

[Ryan Reno]

I'll go ahead and close as working correctly. If you feel like the behavior is incorrect or if the spec should change I would encourage you to file a bug against the CSP spec here: https://github.com/w3c/webappsec-csp/issues