Summary
The media embed renderer trusts serialized provider or sourceUrl metadata and skips the URL protocol validation that normally blocks unsafe media embed URLs. A crafted Plate document can set a known video provider while keeping url as a javascript: iframe source. When a victim opens that document in an app using the registry media embed component, the component renders the attacker URL directly as an iframe src.
Impact
An attacker who can create or share Plate document content with another user can execute JavaScript in the victim browser context when the victim opens the document. This can expose application data available to the page and perform actions as the victim, depending on the host application's session model.
Reproduction
Use a Plate editor or viewer that renders media embeds with the registry MediaEmbedElement and load a document containing this node:
{
"type": "media_embed",
"provider": "vimeo",
"sourceUrl": "https://vimeo.com/1",
"url": "javascript:parent.postMessage('plate-media-xss','*')",
"children": [{ "text": "" }]
}When rendered, the node is treated as a Vimeo media embed because provider is present. The iframe receives the unvalidated url value as its src.
Root Cause / Technical Details
parseMediaUrl is the intended hardening point for media embed URLs and rejects parser output unless the URL protocol is http: or https:. However, useMediaState had a fast path for serialized nodes that already contain provider or sourceUrl. That fast path returned { id, provider, sourceUrl, url } directly and did not call parseMediaUrl or otherwise validate the stored url.
The registry MediaEmbedElement then checks that embed.provider is one of the video providers and renders non-YouTube video providers with <iframe src={embed.url}>. Because provider is attacker-controlled serialized document metadata, it can be set to vimeo while url remains javascript:....
This is fixed in @platejs/media 53.1.4 by recomputing embed metadata from the render URL instead of trusting serialized provider, id, or sourceUrl metadata.
PoC Evidence
A browser proof using the same data flow set an iframe src to:
javascript:parent.postMessage('plate-media-xss','*')
Chromium executed the iframe JavaScript and the parent page received plate-media-xss, confirming execution from the iframe source.
Remediation
Upgrade @platejs/media to 53.1.4 or later. Treat provider, sourceUrl, and id in serialized documents as untrusted derived metadata. Recompute embed metadata from url with parseMediaUrl, or at minimum validate any fast-path url with the same protocol allowlist before rendering an iframe.
References
DavidCarliez Reporter
Summary
The media embed renderer trusts serialized
providerorsourceUrlmetadata and skips the URL protocol validation that normally blocks unsafe media embed URLs. A crafted Plate document can set a known video provider while keepingurlas ajavascript:iframe source. When a victim opens that document in an app using the registry media embed component, the component renders the attacker URL directly as an iframesrc.Impact
An attacker who can create or share Plate document content with another user can execute JavaScript in the victim browser context when the victim opens the document. This can expose application data available to the page and perform actions as the victim, depending on the host application's session model.
Reproduction
Use a Plate editor or viewer that renders media embeds with the registry
MediaEmbedElementand load a document containing this node:{ "type": "media_embed", "provider": "vimeo", "sourceUrl": "https://vimeo.com/1", "url": "javascript:parent.postMessage('plate-media-xss','*')", "children": [{ "text": "" }] }When rendered, the node is treated as a Vimeo media embed because
provideris present. The iframe receives the unvalidatedurlvalue as itssrc.Root Cause / Technical Details
parseMediaUrlis the intended hardening point for media embed URLs and rejects parser output unless the URL protocol ishttp:orhttps:. However,useMediaStatehad a fast path for serialized nodes that already containproviderorsourceUrl. That fast path returned{ id, provider, sourceUrl, url }directly and did not callparseMediaUrlor otherwise validate the storedurl.The registry
MediaEmbedElementthen checks thatembed.provideris one of the video providers and renders non-YouTube video providers with<iframe src={embed.url}>. Becauseprovideris attacker-controlled serialized document metadata, it can be set tovimeowhileurlremainsjavascript:....This is fixed in
@platejs/media53.1.4 by recomputing embed metadata from the render URL instead of trusting serializedprovider,id, orsourceUrlmetadata.PoC Evidence
A browser proof using the same data flow set an iframe
srcto:Chromium executed the iframe JavaScript and the parent page received
plate-media-xss, confirming execution from the iframe source.Remediation
Upgrade
@platejs/mediato 53.1.4 or later. Treatprovider,sourceUrl, andidin serialized documents as untrusted derived metadata. Recompute embed metadata fromurlwithparseMediaUrl, or at minimum validate any fast-pathurlwith the same protocol allowlist before rendering an iframe.References