diff --git a/packages/app-mobile/components/NoteEditor/RichTextEditor.test.tsx b/packages/app-mobile/components/NoteEditor/RichTextEditor.test.tsx
index 4319ccf780..147b0c89db 100644
--- a/packages/app-mobile/components/NoteEditor/RichTextEditor.test.tsx
+++ b/packages/app-mobile/components/NoteEditor/RichTextEditor.test.tsx
@@ -288,6 +288,26 @@ describe('RichTextEditor', () => {
 		});
 	});
 
+	it('should avoid rendering URLs with unknown protocols', async () => {
+		let body = '[link](unknown://test)';
+
+		render(<WrappedEditor
+			noteBody={body}
+			onBodyChange={newBody => { body = newBody; }}
+		/>);
+
+		const renderedLink = await findElement<HTMLAnchorElement>('a[href][data-original-href]');
+		expect(renderedLink.getAttribute('href')).toBe('#');
+		expect(renderedLink.getAttribute('data-original-href')).toBe('unknown://test');
+
+		const window = await getEditorWindow();
+		mockTyping(window, ' testing');
+
+		await waitFor(async () => {
+			expect(body.trim()).toBe('[link](unknown://test) testing');
+		});
+	});
+
 	it.each([
 		MarkupLanguage.Markdown, MarkupLanguage.Html,
 	])('should preserve image attachments on edit (case %#)', async (markupLanguage) => {
diff --git a/packages/app-mobile/contentScripts/richTextEditorBundle/contentScript/index.ts b/packages/app-mobile/contentScripts/richTextEditorBundle/contentScript/index.ts
index 65bbee572f..4644079fca 100644
--- a/packages/app-mobile/contentScripts/richTextEditorBundle/contentScript/index.ts
+++ b/packages/app-mobile/contentScripts/richTextEditorBundle/contentScript/index.ts
@@ -10,6 +10,24 @@ import convertHtmlToMarkdown from './convertHtmlToMarkdown';
 import { ExportedWebViewGlobals as MarkdownEditorWebViewGlobals } from '../../markdownEditorBundle/types';
 import { EditorEventType } from '@joplin/editor/events';
 
+const postprocessHtml = (html: HTMLElement) => {
+	// Fix resource URLs
+	const resources = html.querySelectorAll<HTMLImageElement>('img[data-resource-id]');
+	for (const resource of resources) {
+		const resourceId = resource.getAttribute('data-resource-id');
+		resource.src = `:/${resourceId}`;
+	}
+
+	// Restore HREFs
+	const links = html.querySelectorAll<HTMLAnchorElement>('a[href="#"][data-original-href]');
+	for (const link of links) {
+		link.href = link.getAttribute('data-original-href');
+		link.removeAttribute('data-original-href');
+	}
+
+	return html;
+};
+
 const wrapHtmlForMarkdownConversion = (html: HTMLElement) => {
 	// Add a container element -- when converting to HTML, Turndown
 	// sometimes doesn't process the toplevel element in the same way
diff --git a/packages/editor/ProseMirror/schema.ts b/packages/editor/ProseMirror/schema.ts
index 4d927a4d50..a6ea4dd6bd 100644
--- a/packages/editor/ProseMirror/schema.ts
+++ b/packages/editor/ProseMirror/schema.ts
@@ -3,6 +3,8 @@ import { nodeSpecs as joplinEditableNodes } from './plugins/joplinEditablePlugin
 import { tableNodes } from 'prosemirror-tables';
 import { nodeSpecs as listNodes } from './plugins/listPlugin';
 import { nodeSpecs as resourcePlaceholderNodes } from './plugins/resourcePlaceholderPlugin';
+import { hasProtocol } from '@joplin/utils/url';
+import { isResourceUrl } from '@joplin/lib/models/utils/resourceUtils';
 import { nodeSpecs as detailsNodes } from './plugins/detailsPlugin';
 
 // For reference, see:
@@ -259,8 +261,15 @@ const marks = {
 			tag: 'a[href]',
 			getAttrs: node => {
 				const resourceId = node.getAttribute('data-resource-id');
-				const href = node.getAttribute('href');
+				let href = node.getAttribute('href');
 				const isResourceLink = resourceId && href === '#';
+				if (isResourceLink) {
+					href = `:/${resourceId}`;
+				}
+
+				if (href === '#' && node.hasAttribute('data-original-href')) {
+					href = node.getAttribute('data-original-href');
+				}
 
 				return {
 					href: isResourceLink ? `:/${resourceId}` : href,
@@ -269,10 +278,29 @@ const marks = {
 				};
 			},
 		}],
-		toDOM: node => [
-			'a',
-			{ href: node.attrs.href, title: node.attrs.title, 'data-resource-id': node.attrs.dataResourceId },
-		],
+		toDOM: node => {
+			const isSafeForRendering = (href: string) => {
+				return hasProtocol(href, ['http', 'https', 'joplin']) || isResourceUrl(href);
+			};
+
+			// Avoid rendering URLs with unknown protocols (avoid rendering or pasting unsafe HREFs).
+			// Note that URL click handling is handled elsewhere and does not use the HTML "href" attribute.
+			// However "href" may be used by the right-click menu on web:
+			const safeHref = isSafeForRendering(node.attrs.href) ? node.attrs.href : '#';
+
+			return [
+				'a',
+				{
+					href: safeHref,
+					...(safeHref !== node.attrs.href ? {
+						'data-original-href': node.attrs.href,
+					} : {}),
+
+					title: node.attrs.title,
+					'data-resource-id': node.attrs.dataResourceId,
+				},
+			];
+		},
 	},
 } satisfies Record<string, MarkSpec>;