README video (user-attachments) blocked by media-src CSP for signed-in users only

[jo-duchan]

🏷️ Discussion Type

Bug

Body

A video embedded in a public repository README plays for signed-out visitors, but for any signed-in account it renders as an empty 0:00 player. The browser blocks the request because the page's Content-Security-Policy is different when you are signed in.

Repository: https://github.com/jo-duchan/tapflow (public)

Embed (README.md, line 40):

<video src="https://github.com/user-attachments/assets/dbba8bde-74b6-4fb9-bdb6-3919bc4295c4" controls width="100%"></video>

Steps to reproduce

1. Open https://github.com/jo-duchan/tapflow in a private window (signed out). The video plays.
2. Sign in with any account and reload. The player stays at 0:00 and never loads.

Console error (signed in, Chrome):

Loading media from 'https://github.com/user-attachments/assets/dbba8bde-74b6-4fb9-bdb6-3919bc4295c4'
violates the following Content Security Policy directive: "media-src github.githubassets.com
user-images.githubusercontent.com secured-user-images.githubusercontent.com
private-user-images.githubusercontent.com". The action has been blocked.

CSP comparison

	media-src
Signed out (response header, 2026-10-10)	github.com user-images.githubusercontent.com secured-user-images.githubusercontent.com private-user-images.githubusercontent.com github-production-user-asset-6210df.s3.amazonaws.com gist.github.com github.githubassets.com
Signed in (from the console error above)	github.githubassets.com user-images.githubusercontent.com secured-user-images.githubusercontent.com private-user-images.githubusercontent.com

The asset URL is on github.com and 302-redirects to github-production-user-asset-6210df.s3.amazonaws.com. Neither host is in the signed-in media-src, so the browser refuses the first request before the redirect happens.

Expected: signed-in users can play the video, as signed-out users can.

Observed: first noticed 2026-10-10, with more than one account. It happens on every signed-in account we tried.

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[RealZST]

Same issue on our repo. Claude Code found the cause and a fix:

With a <video> tag, GitHub doesn't rewrite the first video in each HTML block to a signed private-user-images.githubusercontent.com URL. It stays on github.com/user-attachments/..., and the signed-in CSP blocks that.

We replaced each <video> tag with the bare attachment URL on its own line, with blank lines around it:

https://github.com/user-attachments/assets/<id>

GitHub rewrites all of these to signed URLs, and all our README videos play again when signed in.

[jo-duchan]

Thanks, that was exactly the issue. I replaced the <video> tag with the bare attachment URL on its own line, and GitHub now renders it with a signed private-user-images.githubusercontent.com URL. The README video plays for signed-in users again (jo-duchan/tapflow#959).

I also checked a few other READMEs with videos. The ones that work for signed-in users all use bare URLs. It would still be nice if GitHub handled <video src> the same way, since it currently fails silently for signed-in users.