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Make allowNetworking testable and throw in AVM2 navigateToURL - #25102
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kjarosh
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kjarosh
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kjarosh
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danielhjacobs
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Nov 5, 2026
Ruffle gave Flash files script access to the page by default. When loading a URL, it sets `allowScriptAccess` to `samedomain`, which is true when the SWF is served from the site's own domain. This let any Flash post call `ExternalInterface` to run JavaScript as the viewer and hijack their account. It also allowed `navigateToURL` and unrestricted network access. Fix it by disabling script access, networking, and URL opening in the Ruffle config, and by running the player inside an `<iframe sandbox="allow-scripts" srcdoc="...">`. The sandboxed frame has an opaque origin, so even if Ruffle has a bug, a malicious Flash file can't access the user's cookies, session, or the parent page. Because the frame's origin is `null`, Ruffle's fetches for the .wasm and .swf files now count as cross-origin. For this reason, the shipped nginx for the prod image now sends `Access-Control-Allow-Origin: *` for .wasm and .swf files only. CDNs serving flash files might need to have their caches purged and/or add this header to these extensions.
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Description
Part of #25100 and #3044.
This is the first step towards more correctly implementing the
allowNetworkingsetting (Restricting networking APIs) that can be used with<object>or<embed>tags. This is mostly just some preliminary architectural work. As a proof of concept I implemented throwing in AVM2'snavigateToURL. I think next we should probably expose this to the desktop app.Afterwards of course all the APIs listed in the Adobe documentation need to be restricted.
Testing
This feature is only available when running the Flash Player inside a browser, so this isn't directly testable with something like
flashplayerdebugger. I did test this using https://hub.docker.com/r/jchprj/play-adobe-flash-after-eol.Checklist