From 010668255d7888f486ca2c58cbdf628ba400ddd2 Mon Sep 17 00:00:00 2001
From: Brennan Benson <79079362+brennanb2025@users.noreply.github.com>
Date: Mon, 20 Jul 2026 17:55:47 -0700
Subject: [PATCH] fix(editor): validate preserved break source

Use the editor model's supported DOM parse-rule type instead of a private duplicate. Exercise the rendered-DOM round trip and reject forged preservation attributes before they can become hidden Markdown source.
---
 .../raw-markdown-html-line-break.test.ts      | 31 +++++++++++++++++--
 .../editor/raw-markdown-html-source-dom.ts    | 25 +++++++--------
 2 files changed, 39 insertions(+), 17 deletions(-)

diff --git a/src/renderer/src/components/editor/raw-markdown-html-line-break.test.ts b/src/renderer/src/components/editor/raw-markdown-html-line-break.test.ts
index 079aa0a085a..f9a0a86dd49 100644
--- a/src/renderer/src/components/editor/raw-markdown-html-line-break.test.ts
+++ b/src/renderer/src/components/editor/raw-markdown-html-line-break.test.ts
@@ -1,3 +1,5 @@
+// @vitest-environment happy-dom
+
 import { describe, expect, it } from 'vitest'
 import { Editor } from '@tiptap/core'
 import type { Node as ProseMirrorNode } from '@tiptap/pm/model'
@@ -62,16 +64,39 @@ describe('raw markdown <br> line breaks in the rich editor', () => {
     }
   })
 
-  it('round-trips the verbatim <br> tags in a table cell on save', () => {
+  it('round-trips verbatim <br> tags after the rendered DOM is parsed again', () => {
     const editor = createEditor(TABLE_WITH_BREAKS)
     try {
+      const rendered = document.createElement('div')
+      rendered.innerHTML = editor.getHTML()
+      expect(rendered.querySelectorAll('br[data-raw-markdown-html-inline]')).toHaveLength(3)
+      expect(rendered.textContent).not.toContain('<br')
+
+      editor.commands.setContent(rendered.innerHTML)
       const output = (editor as Editor & { getMarkdown(): string }).getMarkdown()
-      expect(output).toContain('<br/>')
-      expect(output).toContain('<br>')
+      expect(output.match(/<br\s*\/?>/g)).toEqual(['<br/>', '<br/>', '<br>'])
       // The break must not silently collapse into a space on serialization.
       expect(output).not.toContain('`normal` `defect`')
     } finally {
       editor.destroy()
     }
   })
+
+  it('does not accept arbitrary Markdown source from a forged break marker', () => {
+    const editor = createEditor('Before<br/>after\n')
+    try {
+      const rendered = document.createElement('div')
+      rendered.innerHTML = editor.getHTML()
+      rendered
+        .querySelector('br[data-raw-markdown-html-inline]')
+        ?.setAttribute('data-raw-markdown-html-value', '<script>alert(1)</script>')
+
+      editor.commands.setContent(rendered.innerHTML)
+      const output = (editor as Editor & { getMarkdown(): string }).getMarkdown()
+      expect(output).toContain('Before<br>after')
+      expect(output).not.toContain('<script>')
+    } finally {
+      editor.destroy()
+    }
+  })
 })
diff --git a/src/renderer/src/components/editor/raw-markdown-html-source-dom.ts b/src/renderer/src/components/editor/raw-markdown-html-source-dom.ts
index 8edad202bb7..24770e6a969 100644
--- a/src/renderer/src/components/editor/raw-markdown-html-source-dom.ts
+++ b/src/renderer/src/components/editor/raw-markdown-html-source-dom.ts
@@ -1,5 +1,5 @@
 import { mergeAttributes } from '@tiptap/core'
-import type { DOMOutputSpec, Node as ProseMirrorNode } from '@tiptap/pm/model'
+import type { DOMOutputSpec, Node as ProseMirrorNode, TagParseRule } from '@tiptap/pm/model'
 import type { RichMarkdownSourceKind } from './rich-markdown-source-transport'
 
 // Why: preserves the exact authored <br> spelling on the rendered break node so
@@ -14,16 +14,17 @@ type RawMarkdownSourceDomConfig = {
   className?: string
 }
 
-type RawMarkdownSourceParseRule = {
-  tag: string
-  priority?: number
-  getAttrs: (element: HTMLElement) => { value: string }
-}
-
 function isHtmlLineBreak(value: string): boolean {
   return /^<br\s*\/?>$/i.test(value.trim())
 }
 
+function parsedHtmlLineBreakValue(element: HTMLElement): string {
+  const value = element.getAttribute(HTML_LINE_BREAK_VALUE_ATTR)
+  // Why: DOM input can come from the clipboard, so only trusted break syntax
+  // may become hidden Markdown source through the internal preservation marker.
+  return value && isHtmlLineBreak(value) ? value : '<br>'
+}
+
 function nodeValue(node: ProseMirrorNode): string {
   return typeof node.attrs.value === 'string' ? node.attrs.value : ''
 }
@@ -34,10 +35,8 @@ function rendersLineBreaks(config: RawMarkdownSourceDomConfig): boolean {
   return config.inline && config.kind === 'inline-html'
 }
 
-export function rawMarkdownSourceParseRules(
-  config: RawMarkdownSourceDomConfig
-): RawMarkdownSourceParseRule[] {
-  const rules: RawMarkdownSourceParseRule[] = [
+export function rawMarkdownSourceParseRules(config: RawMarkdownSourceDomConfig): TagParseRule[] {
+  const rules: TagParseRule[] = [
     {
       tag: `${config.inline ? 'span' : 'div'}[${config.marker}]`,
       getAttrs: (element: HTMLElement) => ({ value: element.textContent ?? '' })
@@ -50,9 +49,7 @@ export function rawMarkdownSourceParseRules(
     rules.push({
       tag: `br[${config.marker}]`,
       priority: 100,
-      getAttrs: (element: HTMLElement) => ({
-        value: element.getAttribute(HTML_LINE_BREAK_VALUE_ATTR) ?? '<br>'
-      })
+      getAttrs: (element: HTMLElement) => ({ value: parsedHtmlLineBreakValue(element) })
     })
   }
   return rules