fix: use targetOrigin in the proxy message relay #40
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Pull Request Overview
This pull request improves security in the proxy message relay by implementing specific target origins in postMessage calls instead of using the wildcard * whenever possible. The change follows security best practices by restricting message destinations to known origins.
Key changes:
- Updated the proxy message handling to use the target URL's origin when posting messages to the iframe
- Reorganized the message event handling logic for better clarity
- Updated documentation to reflect the security improvement and explain the rationale
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| packages/client/scripts/proxy/index.html | Implements targetOrigin security improvement and reorganizes message handling logic |
| docs/src/guide/client/using-a-proxy.md | Updates documentation to explain the importance of using specific targetOrigin values |
Comments suppressed due to low confidence (1)
packages/client/scripts/proxy/index.html:38
- [nitpick] The variable name 'e' is not descriptive. Consider using '' or 'error' if the caught exception will be used, or keep '' if it's intentionally ignored.
} catch (e) {
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| Branch Preview URL: | https://fix-proxy-messages.mcp-ui.pages.dev |
liady
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Jul 18, 2025
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## [5.1.2](v5.1.1...v5.1.2) (2025-07-18) ### Bug Fixes * use targetOrigin in the proxy message relay ([#40](#40)) ([b3fb54e](b3fb54e))
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# 1.0.0 (2025-07-19) ### Bug Fixes * add a bridge to pass messages in and out of the proxy ([#38](#38)) ([30ccac0](30ccac0)) * **client:** specify iframe ([fd0b70a](fd0b70a)) * **client:** styling ([6ff9b68](6ff9b68)) * dependencies ([887f61f](887f61f)) * export RemoteDomResource ([2b86f2d](2b86f2d)) * export ResourceRenderer and HtmlResource ([2b841a5](2b841a5)) * exports ([3a93a16](3a93a16)) * iframe handle ([#15](#15)) ([66bd4fd](66bd4fd)) * lint ([4487820](4487820)) * lint ([d0a91f9](d0a91f9)) * package config ([8dc1e53](8dc1e53)) * packaging ([9e6babd](9e6babd)) * pass ref explicitly using iframeProps ([#33](#33)) ([d01b5d1](d01b5d1)) * publish ([0943e7a](0943e7a)) * ref passing to UIResourceRenderer ([#32](#32)) ([d28c23f](d28c23f)) * remove shared dependency ([e66e8f4](e66e8f4)) * rename components and methods to fit new scope ([#22](#22)) ([6bab1fe](6bab1fe)) * rename delivery -> encoding and flavor -> framework ([#36](#36)) ([9a509ed](9a509ed)) * support react-router ([21ffb95](21ffb95)) * text and blob support in RemoteDOM resources ([ec68eb9](ec68eb9)) * trigger release ([aaca831](aaca831)) * typescript types to be compatible with MCP SDK ([#10](#10)) ([74365d7](74365d7)) * update deps ([4091ef4](4091ef4)) * use targetOrigin in the proxy message relay ([#40](#40)) ([b3fb54e](b3fb54e)) * validate URL ([b7c994d](b7c994d)) ### Documentation * bump ([#4](#4)) ([ad4d163](ad4d163)) ### Features * add proxy option to externalUrl ([#37](#37)) ([7b95cd0](7b95cd0)) * add remote-dom content type ([#18](#18)) ([5dacf37](5dacf37)) * add Ruby server SDK ([#31](#31)) ([5ffcde4](5ffcde4)) * change onGenericMcpAction to optional onUiAction ([1913b59](1913b59)) * **client:** allow setting supportedContentTypes for HtmlResource ([#17](#17)) ([e009ef1](e009ef1)) * consolidate ui:// and ui-app:// ([#8](#8)) ([2e08035](2e08035)) * pass iframe props down ([#14](#14)) ([112539d](112539d)) * separate html and remote-dom props ([#24](#24)) ([a7f0529](a7f0529)) * support generic messages response ([#35](#35)) ([10b407b](10b407b)) * support ui action result types ([#6](#6)) ([899d152](899d152)) * switch to ResourceRenderer ([#21](#21)) ([6fe3166](6fe3166)) ### BREAKING CHANGES * The existing naming is ambiguous. Renaming delivery to encoding and flavor to framework should clarify the intent. * exported names have changed * removed deprecated client API * (previous one didn't take due to semantic-release misalignment)
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# 1.0.0-alpha.1 (2025-10-10) ### Bug Fixes * adapter version ([259c842](259c842)) * add a bridge to pass messages in and out of the proxy ([#38](#38)) ([30ccac0](30ccac0)) * bump client version ([75c9236](75c9236)) * **client:** specify iframe ([fd0b70a](fd0b70a)) * **client:** styling ([6ff9b68](6ff9b68)) * dependencies ([887f61f](887f61f)) * export RemoteDomResource ([2b86f2d](2b86f2d)) * export ResourceRenderer and HtmlResource ([2b841a5](2b841a5)) * exports ([3a93a16](3a93a16)) * iframe handle ([#15](#15)) ([66bd4fd](66bd4fd)) * lint ([4487820](4487820)) * lint ([d0a91f9](d0a91f9)) * minor typo ([a0bee9c](a0bee9c)) * move react dependencies to be peer dependencies ([#91](#91)) ([f672f3e](f672f3e)), closes [#90](#90) * package config ([8dc1e53](8dc1e53)) * packaging ([9e6babd](9e6babd)) * pass ref explicitly using iframeProps ([#33](#33)) ([d01b5d1](d01b5d1)) * publish ([0943e7a](0943e7a)) * ref passing to UIResourceRenderer ([#32](#32)) ([d28c23f](d28c23f)) * release ([420efc0](420efc0)) * remove shared dependency ([e66e8f4](e66e8f4)) * rename components and methods to fit new scope ([#22](#22)) ([6bab1fe](6bab1fe)) * rename delivery -> encoding and flavor -> framework ([#36](#36)) ([9a509ed](9a509ed)) * Ruby comment ([b22dc2e](b22dc2e)) * support react-router ([21ffb95](21ffb95)) * text and blob support in RemoteDOM resources ([ec68eb9](ec68eb9)) * trigger release ([aaca831](aaca831)) * typescript ci publish ([e7c0ebf](e7c0ebf)) * typescript types to be compatible with MCP SDK ([#10](#10)) ([74365d7](74365d7)) * update deps ([4091ef4](4091ef4)) * update isUIResource to use EmbeddedResource type ([#122](#122)) ([5a65a0b](5a65a0b)), closes [#117](#117) * use targetOrigin in the proxy message relay ([#40](#40)) ([b3fb54e](b3fb54e)) * validate URL ([b7c994d](b7c994d)) * wc dist overwrite ([#63](#63)) ([9e46c56](9e46c56)) ### Documentation * bump ([#4](#4)) ([ad4d163](ad4d163)) ### Features * add adapters infra (appssdk) ([#125](#125)) ([2e016cd](2e016cd)) * add convenience function isUIResource to client SDK ([#86](#86)) ([607c6ad](607c6ad)) * add embeddedResourceProps for annotations ([#99](#99)) ([b96ec44](b96ec44)) * add proxy option to externalUrl ([#37](#37)) ([7b95cd0](7b95cd0)) * add remote-dom content type ([#18](#18)) ([5dacf37](5dacf37)) * add Ruby server SDK ([#31](#31)) ([5ffcde4](5ffcde4)) * add sandbox permissions instead of an override ([#83](#83)) ([b1068e9](b1068e9)) * add ui-request-render-data message type ([#111](#111)) ([26135ce](26135ce)) * add UIResourceRenderer Web Component ([#58](#58)) ([ec8f299](ec8f299)) * auto resize with the autoResizeIframe prop ([#56](#56)) ([76c867a](76c867a)) * change onGenericMcpAction to optional onUiAction ([1913b59](1913b59)) * **client:** allow setting supportedContentTypes for HtmlResource ([#17](#17)) ([e009ef1](e009ef1)) * consolidate ui:// and ui-app:// ([#8](#8)) ([2e08035](2e08035)) * pass iframe props down ([#14](#14)) ([112539d](112539d)) * refactor UTFtoB64 (bump server version) ([#95](#95)) ([2d5e16b](2d5e16b)) * send render data to the iframe ([#51](#51)) ([d38cfc7](d38cfc7)) * separate html and remote-dom props ([#24](#24)) ([a7f0529](a7f0529)) * support generic messages response ([#35](#35)) ([10b407b](10b407b)) * support passing resource metadata ([#87](#87)) ([f1c1c9b](f1c1c9b)) * support ui action result types ([#6](#6)) ([899d152](899d152)) * switch to ResourceRenderer ([#21](#21)) ([6fe3166](6fe3166)) ### BREAKING CHANGES * The existing naming is ambiguous. Renaming delivery to encoding and flavor to framework should clarify the intent. * exported names have changed * removed deprecated client API * (previous one didn't take due to semantic-release misalignment)
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# 1.0.0-alpha.1 (2025-10-10) ### Bug Fixes * adapter version ([259c842](259c842)) * add a bridge to pass messages in and out of the proxy ([#38](#38)) ([30ccac0](30ccac0)) * bump client version ([75c9236](75c9236)) * **client:** specify iframe ([fd0b70a](fd0b70a)) * **client:** styling ([6ff9b68](6ff9b68)) * dependencies ([887f61f](887f61f)) * export RemoteDomResource ([2b86f2d](2b86f2d)) * export ResourceRenderer and HtmlResource ([2b841a5](2b841a5)) * exports ([3a93a16](3a93a16)) * iframe handle ([#15](#15)) ([66bd4fd](66bd4fd)) * lint ([4487820](4487820)) * lint ([d0a91f9](d0a91f9)) * minor typo ([a0bee9c](a0bee9c)) * move react dependencies to be peer dependencies ([#91](#91)) ([f672f3e](f672f3e)), closes [#90](#90) * package config ([8dc1e53](8dc1e53)) * packaging ([9e6babd](9e6babd)) * pass ref explicitly using iframeProps ([#33](#33)) ([d01b5d1](d01b5d1)) * publish ([0943e7a](0943e7a)) * ref passing to UIResourceRenderer ([#32](#32)) ([d28c23f](d28c23f)) * release ([420efc0](420efc0)) * remove shared dependency ([e66e8f4](e66e8f4)) * rename components and methods to fit new scope ([#22](#22)) ([6bab1fe](6bab1fe)) * rename delivery -> encoding and flavor -> framework ([#36](#36)) ([9a509ed](9a509ed)) * Ruby comment ([b22dc2e](b22dc2e)) * server versioning ([2324371](2324371)) * support react-router ([21ffb95](21ffb95)) * text and blob support in RemoteDOM resources ([ec68eb9](ec68eb9)) * trigger release ([aaca831](aaca831)) * typescript ci publish ([e7c0ebf](e7c0ebf)) * typescript types to be compatible with MCP SDK ([#10](#10)) ([74365d7](74365d7)) * update deps ([4091ef4](4091ef4)) * update isUIResource to use EmbeddedResource type ([#122](#122)) ([5a65a0b](5a65a0b)), closes [#117](#117) * use targetOrigin in the proxy message relay ([#40](#40)) ([b3fb54e](b3fb54e)) * validate URL ([b7c994d](b7c994d)) * wc dist overwrite ([#63](#63)) ([9e46c56](9e46c56)) ### Documentation * bump ([#4](#4)) ([ad4d163](ad4d163)) ### Features * add adapters infra (appssdk) ([#125](#125)) ([2e016cd](2e016cd)) * add convenience function isUIResource to client SDK ([#86](#86)) ([607c6ad](607c6ad)) * add embeddedResourceProps for annotations ([#99](#99)) ([b96ec44](b96ec44)) * add proxy option to externalUrl ([#37](#37)) ([7b95cd0](7b95cd0)) * add remote-dom content type ([#18](#18)) ([5dacf37](5dacf37)) * add Ruby server SDK ([#31](#31)) ([5ffcde4](5ffcde4)) * add sandbox permissions instead of an override ([#83](#83)) ([b1068e9](b1068e9)) * add ui-request-render-data message type ([#111](#111)) ([26135ce](26135ce)) * add UIResourceRenderer Web Component ([#58](#58)) ([ec8f299](ec8f299)) * auto resize with the autoResizeIframe prop ([#56](#56)) ([76c867a](76c867a)) * change onGenericMcpAction to optional onUiAction ([1913b59](1913b59)) * **client:** allow setting supportedContentTypes for HtmlResource ([#17](#17)) ([e009ef1](e009ef1)) * consolidate ui:// and ui-app:// ([#8](#8)) ([2e08035](2e08035)) * pass iframe props down ([#14](#14)) ([112539d](112539d)) * refactor UTFtoB64 (bump server version) ([#95](#95)) ([2d5e16b](2d5e16b)) * send render data to the iframe ([#51](#51)) ([d38cfc7](d38cfc7)) * separate html and remote-dom props ([#24](#24)) ([a7f0529](a7f0529)) * support generic messages response ([#35](#35)) ([10b407b](10b407b)) * support passing resource metadata ([#87](#87)) ([f1c1c9b](f1c1c9b)) * support ui action result types ([#6](#6)) ([899d152](899d152)) * switch to ResourceRenderer ([#21](#21)) ([6fe3166](6fe3166)) ### BREAKING CHANGES * The existing naming is ambiguous. Renaming delivery to encoding and flavor to framework should clarify the intent. * exported names have changed * removed deprecated client API * (previous one didn't take due to semantic-release misalignment)
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# 1.0.0 (2025-11-04) ### Bug Fixes * add a bridge to pass messages in and out of the proxy ([#38](#38)) ([30ccac0](30ccac0)) * bump client version ([75c9236](75c9236)) * **client:** specify iframe ([fd0b70a](fd0b70a)) * **client:** styling ([6ff9b68](6ff9b68)) * dependencies ([887f61f](887f61f)) * Enable bidirectional message relay in rawhtml proxy mode ([#138](#138)) ([f0bdefb](f0bdefb)) * ensure Apps SDK adapter is bundled properly and initialized wth config ([#137](#137)) ([4f7c25c](4f7c25c)) * export RemoteDomResource ([2b86f2d](2b86f2d)) * export ResourceRenderer and HtmlResource ([2b841a5](2b841a5)) * exports ([3a93a16](3a93a16)) * fix file extension reference in package.json ([927989c](927989c)) * iframe handle ([#15](#15)) ([66bd4fd](66bd4fd)) * lint ([4487820](4487820)) * lint ([d0a91f9](d0a91f9)) * minor typo ([a0bee9c](a0bee9c)) * move react dependencies to be peer dependencies ([#91](#91)) ([f672f3e](f672f3e)), closes [#90](#90) * package config ([8dc1e53](8dc1e53)) * packaging ([9e6babd](9e6babd)) * pass ref explicitly using iframeProps ([#33](#33)) ([d01b5d1](d01b5d1)) * publish ([0943e7a](0943e7a)) * ref passing to UIResourceRenderer ([#32](#32)) ([d28c23f](d28c23f)) * remove shared dependency ([e66e8f4](e66e8f4)) * rename components and methods to fit new scope ([#22](#22)) ([6bab1fe](6bab1fe)) * rename delivery -> encoding and flavor -> framework ([#36](#36)) ([9a509ed](9a509ed)) * Ruby comment ([b22dc2e](b22dc2e)) * support react-router ([21ffb95](21ffb95)) * text and blob support in RemoteDOM resources ([ec68eb9](ec68eb9)) * trigger release ([aaca831](aaca831)) * typescript ci publish ([e7c0ebf](e7c0ebf)) * typescript types to be compatible with MCP SDK ([#10](#10)) ([74365d7](74365d7)) * update deps ([4091ef4](4091ef4)) * update isUIResource to use EmbeddedResource type ([#122](#122)) ([5a65a0b](5a65a0b)), closes [#117](#117) * use targetOrigin in the proxy message relay ([#40](#40)) ([b3fb54e](b3fb54e)) * validate URL ([b7c994d](b7c994d)) * wc dist overwrite ([#63](#63)) ([9e46c56](9e46c56)) ### Documentation * bump ([#4](#4)) ([ad4d163](ad4d163)) ### Features * add convenience function isUIResource to client SDK ([#86](#86)) ([607c6ad](607c6ad)) * add embeddedResourceProps for annotations ([#99](#99)) ([b96ec44](b96ec44)) * add proxy option to externalUrl ([#37](#37)) ([7b95cd0](7b95cd0)) * add remote-dom content type ([#18](#18)) ([5dacf37](5dacf37)) * add Ruby server SDK ([#31](#31)) ([5ffcde4](5ffcde4)) * add sandbox permissions instead of an override ([#83](#83)) ([b1068e9](b1068e9)) * add ui-request-render-data message type ([#111](#111)) ([26135ce](26135ce)) * add UIResourceRenderer Web Component ([#58](#58)) ([ec8f299](ec8f299)) * auto resize with the autoResizeIframe prop ([#56](#56)) ([76c867a](76c867a)) * change onGenericMcpAction to optional onUiAction ([1913b59](1913b59)) * **client:** allow setting supportedContentTypes for HtmlResource ([#17](#17)) ([e009ef1](e009ef1)) * consolidate ui:// and ui-app:// ([#8](#8)) ([2e08035](2e08035)) * pass iframe props down ([#14](#14)) ([112539d](112539d)) * refactor UTFtoB64 (bump server version) ([#95](#95)) ([2d5e16b](2d5e16b)) * send render data to the iframe ([#51](#51)) ([d38cfc7](d38cfc7)) * separate html and remote-dom props ([#24](#24)) ([a7f0529](a7f0529)) * support adapters ([#127](#127)) ([d4bd152](d4bd152)) * support generic messages response ([#35](#35)) ([10b407b](10b407b)) * support metadata in Python SDK ([#134](#134)) ([9bc3c64](9bc3c64)) * support passing resource metadata ([#87](#87)) ([f1c1c9b](f1c1c9b)) * support proxy for rawHtml ([#132](#132)) ([1bbeb09](1bbeb09)) * support ui action result types ([#6](#6)) ([899d152](899d152)) * switch to ResourceRenderer ([#21](#21)) ([6fe3166](6fe3166)) ### BREAKING CHANGES * The existing naming is ambiguous. Renaming delivery to encoding and flavor to framework should clarify the intent. * exported names have changed * removed deprecated client API * (previous one didn't take due to semantic-release misalignment)
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Improve security by specifying the origin instead of
*(whenever possible)