Bug 308752 – blob: URLs are allowed in <iframe>s when CSP’s `frame-src` contains `‘self’`.

• Status: RESOLVED
• Resolution: FIXED
• Component: Page Loading

Created attachment 478498 [details]
Test for reproduction

Version: WebKitGTK MiniBrowser 2.50.4, 2.47.0

OS: Ubuntu 22.04.3 LTS

Description:
When `Content-Security-Policy: frame-src ‘self’` is set, an <iframe> whose `src` attribute is a blob: URL is allowed to load.

The attached test sets the response header `Content-Security-Policy: frame-src 'self' ` and dynamically creates an <iframe> whose `src` attribute is set to a blob: URL. The embedded document prints the word “run” to the console when it is loaded.

Steps to Reproduce:
1) Serve the attached files from an HTTP web server with PHP enabled.
2) Visit self-enables-blob-frame-src.php.
3) Open the browser console and observe whether “run” is printed.

Observed Behavior:
The <iframe> is loaded and the console prints “run”.

Expected Behavior:
For <iframe> documents loaded from blob: URLs to be allowed, the blob: scheme should be explicitly listed in the `frame-src` directive.

Comparison with other Major Browsers:
Chrome, Opera, Brave, Edge, Firefox and Tor block the <iframe> and do not print “run”.

Important Notes:
- This behavior is observed only for the `frame-src` directive.
- This behavior is not observed in the `frame-src` directive’s fallbacks (`child-src` and `default-src`) and `object-src`.

[Radar WebKit Bug Importer]

<rdar://problem/171268629>

[Kristian Monsen]

Minor spec compliance, and not a security issue.

Pull request: https://github.com/WebKit/WebKit/pull/60814

[EWS]

Committed 309559@main (70534942aada): <https://commits.webkit.org/309559@main>

Reviewed commits have been landed. Closing PR #60814 and removing active labels.