GHSA-qj6x-xx2h-8hvv: XSS
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:
json { "type": "mediaembed", "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:
text 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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/@platejs/mediato a version that resolves this vulnerability.Fixed in 53.1.4 - Upgrade
Upgrade
@platejs/mediato a version that resolves this vulnerability.Fixed in 53.1.4 - Configuration
Update the renderer logic so that when rendering serialized media embed nodes, embed metadata is recomputed from the render URL (using parseMediaUrl) instead of trusting serialized provider/sourceUrl/id fast-path values; validate any iframe src with the same protocol allowlist (http:/https:) before rendering <iframe src={embed.url}>.
Plate media embed renderer (MediaEmbedElement / useMediaState) media embed URL validation behavior for serialized nodes = Recompute embed metadata from the render URL using parseMediaUrl (do not trust serialized provider/sourceUrl/id fast-path) and validate URL protocol via parseMediaUrl allowing only http:/https:
Event History
Frequently Asked Questions
Which applications are exposed?
Applications that render Plate documents using the registry MediaEmbedElement are exposed when they render attacker-controlled media embed nodes. The issue is relevant where users can create or share documents that other users open.
What does an attacker need to exploit this?
The attacker needs the ability to create or share Plate document content that a victim will open. They can supply serialized provider or sourceUrl metadata for a known video provider while setting the embed url to a javascript: URL.
How can potentially malicious document content be identified?
Inspect media_embed nodes for a provider or sourceUrl that identifies a supported provider together with an unsafe url value, such as a javascript: URL. The provided proof of concept uses provider "vimeo" and a javascript: iframe source.