feat: add sandboxing when appending to DOM in importSVG#3543
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Pull request overview
Adds a sandboxed Paper.js import pipeline so untrusted SVGs are no longer appended into the main document during importSvg, reducing XSS risk while preserving the existing PaperCanvas post-import flow.
Changes:
- Route
PaperCanvas.importSvgthrough a sandboxed iframe that runspaper.project.importSVGand returns Paper.js JSON + viewBox data. - Introduce
getPaperSandbox()(lazy singleton) andcreatePaperImportScript()to boot Paper.js inside the sandbox. - Update/add unit tests to assert sanitizer output is what gets sent to the sandbox and to cover script-string generation.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
| File | Description |
|---|---|
src/containers/paper-canvas.jsx |
Switches SVG import to sandbox-based importSVG + importJSON flow with generation-based staleness guard. |
src/helper/paper-sandbox.js |
Adds lazy singleton sandbox creation and dynamic import of Paper.js source. |
src/helper/paper-import-script.js |
Generates the sandbox iframe script that evals Paper.js and handles SVG import requests. |
test/unit/sanitize-svg-import.test.js |
Updates integration test to verify sanitized SVG is sent to the sandbox. |
test/unit/paper-import-script.test.js |
Adds unit coverage for script generation/embedding behavior. |
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| importSvg (svg, rotationCenterX, rotationCenterY) { | ||
| const paperCanvas = this; | ||
| this._importGeneration += 1; | ||
| const generation = this._importGeneration; | ||
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| const createPaperImportScript = paperJsSource => { | ||
| const paperSourceLiteral = JSON.stringify(paperJsSource); | ||
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| // The script is eval'd inside the sandboxed iframe. It must use only | ||
| // ES5-compatible syntax (no arrow functions, no const/let in loops) | ||
| // for maximum browser compatibility, since the iframe runs whatever | ||
| // the browser ships natively — no transpilation. | ||
| return `(function () { | ||
| // Evaluate Paper.js; it declares a global 'paper' variable via its | ||
| // UMD wrapper: var paper = function(...){...}.call(this, ...) | ||
| (0, eval)(${paperSourceLiteral}); | ||
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| test('JSON-escapes special characters in Paper.js source', () => { | ||
| const sourceWithSpecialChars = 'var x = "hello\\nworld"; // comment with </script>'; | ||
| const script = createPaperImportScript(sourceWithSpecialChars); | ||
| expect(script).toContain(JSON.stringify(sourceWithSpecialChars)); | ||
| expect(script).toMatch(/^\(function \(\) \{/); | ||
| expect(script).toMatch(/\}\)\(\);$/); |
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Resolves
https://scratchfoundation.atlassian.net/browse/UEPR-231
Proposed Changes
Use SVG sandboxing implemented in https://github.com/scratchfoundation/scratch-editor/pull/567/changes when appending SVGs to the DOM in
importSVGTODO: Update references of scratch-svg-renderer to a version exporting sandbox
Reason for Changes
Currently we attempt to sanitize SVGs, but the approach is piecemeal. The biggest security issue in the current state is that we load SVGs directly into the DOM (in scratch-paint that happens so that they can be converted in the format that paperJS expects), which is an inherently unsafe operation.