Merge pull request 'fix(outbox): two tabs no longer overwrite each other's queue (#268)' (#430) from fix/outbox-multi-tab into lotus

#266: remembered widget approvals (lotus.widgetConsent.*) survived logout,
so they applied silently to the next account on the device and listed the
previous account's rooms; clearPlaintextCaches now sweeps them. Space
structure, call membership and Lotus room-policy state join
PROTECTED_STATE_TYPES, so no widget can be granted them.

#267: any website could auto-submit a form to /share-target and land the
user in the share picker with attacker-chosen text and files. The worker
now refuses a share whose Origin is another site. (Sec-Fetch-Site, as the
issue suggested, never reaches a service worker: checked in Chromium.)
Origin null/absent, as the OS share sheet sends, stays accepted, and
/share now says the content came from another app or website. Both logout
paths await clearSharedPayload(); the server-forced one also clears the
soundboard clip cache, as #57 intended.

Fixes #266
Fixes #267

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/features/bookmarks/BookmarksPanel.css.ts

@@ -1,10 +1,11 @@
 import { style } from '@vanilla-extract/css';
-import { config, toRem } from 'folds';
+import { config } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../styles/sidePanel';
 
-// Mirrors MembersDrawer: a 266px side panel on desktop that becomes a
+// Mirrors MembersDrawer: a side panel (shared width) on desktop that becomes a
 // full-screen fixed panel on narrow viewports — the app's canonical drawer.
 export const BookmarksPanel = style({
-  width: toRem(266),
+  width: SIDE_PANEL_WIDTH,
   '@media': {
     '(max-width: 750px)': {
       position: 'fixed',

src/app/features/common-settings/general/RoomProfile.tsx

@@ -52,8 +52,7 @@ import { settingsAtom } from '../../../state/settings';
 import { AsyncStatus, useAsyncCallback } from '../../../hooks/useAsyncCallback';
 import { useAlive } from '../../../hooks/useAlive';
 import { RoomPermissionsAPI } from '../../../hooks/useRoomPermissions';
-
-const MARKDOWN_PATTERN = /(\*\*|__|\*|_|~~|`|\[.+?\]\(.+?\))/;
+import { buildTopicContent } from '../../../utils/topicMarkdown';
 
 function wrapSelection(textarea: HTMLTextAreaElement, syntax: string, placeholder: string) {
   const start = textarea.selectionStart;
@@ -71,30 +70,6 @@ function wrapSelection(textarea: HTMLTextAreaElement, syntax: string, placeholde
   textarea.setSelectionRange(cursorStart, cursorEnd);
 }
 
-function topicMarkdownToHtml(text: string): string {
-  return text
-    .replace(/&/g, '&')
-    .replace(/</g, '&lt;')
-    .replace(/>/g, '&gt;')
-    .replace(/\*\*(.+?)\*\*/g, '<strong>$1</strong>')
-    .replace(/__(.+?)__/g, '<strong>$1</strong>')
-    .replace(/\*(.+?)\*/g, '<em>$1</em>')
-    .replace(/_(.+?)_/g, '<em>$1</em>')
-    .replace(/~~(.+?)~~/g, '<del>$1</del>')
-    .replace(/`(.+?)`/g, '<code>$1</code>')
-    .replace(/\[(.+?)\]\((.+?)\)/g, '<a href="$2">$1</a>')
-    .replace(/\n/g, '<br>');
-}
-
-function buildTopicContent(topic: string): Record<string, string> {
-  if (!MARKDOWN_PATTERN.test(topic)) return { topic };
-  const formattedBody = topicMarkdownToHtml(topic);
-  // Use HTML-stripped text as the plain topic so the header shows clean text, not raw markdown syntax
-  const plainTopic = formattedBody.replace(/<br>/g, '\n').replace(/<[^>]+>/g, '');
-
-  return { topic: plainTopic, format: 'org.matrix.custom.html', formatted_body: formattedBody };
-}
-
 type RoomProfileEditProps = {
   canEditAvatar: boolean;
   canEditName: boolean;

src/app/features/room/MediaGallery.css.ts

@@ -1,13 +1,13 @@
 import { style } from '@vanilla-extract/css';
 import { color, config, toRem } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../styles/sidePanel';
 
 // Right-side drawer DOCKED into the room layout row (a flex sibling of the
-// timeline), exactly like MembersDrawer — not a floating overlay. 320px is a
-// little wider than the 266px member/bookmark drawers because it hosts a media
-// grid. On narrow viewports it becomes a full-screen fixed panel, matching the
-// app's other drawers.
+// timeline), exactly like MembersDrawer — not a floating overlay. Same width as
+// every other right-hand panel (styles/sidePanel.ts, #263). On narrow viewports
+// it becomes a full-screen fixed panel, matching the app's other drawers.
 export const MediaGalleryDrawer = style({
-  width: toRem(320),
+  width: SIDE_PANEL_WIDTH,
   overflow: 'hidden',
   '@media': {
     '(max-width: 750px)': {

src/app/features/room/MembersDrawer.css.ts

@@ -1,8 +1,9 @@
 import { keyframes, style } from '@vanilla-extract/css';
-import { config, toRem } from 'folds';
+import { config } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../styles/sidePanel';
 
 export const MembersDrawer = style({
-  width: toRem(266),
+  width: SIDE_PANEL_WIDTH,
   '@media': {
     '(max-width: 750px)': {
       position: 'fixed',

src/app/features/room/thread/ThreadPanel.css.ts

@@ -1,8 +1,9 @@
 import { style } from '@vanilla-extract/css';
-import { config, toRem } from 'folds';
+import { config } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../../styles/sidePanel';
 
 export const ThreadPanel = style({
-  width: toRem(360),
+  width: SIDE_PANEL_WIDTH,
   '@media': {
     '(max-width: 750px)': {
       position: 'fixed',

src/app/features/room/thread/ThreadsListPanel.css.ts

@@ -1,8 +1,9 @@
 import { style } from '@vanilla-extract/css';
-import { color, config, toRem } from 'folds';
+import { color, config } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../../styles/sidePanel';
 
 export const ThreadsListPanel = style({
-  width: toRem(340),
+  width: SIDE_PANEL_WIDTH,
   '@media': {
     '(max-width: 750px)': {
       position: 'fixed',

src/app/features/room/widgets/WidgetsPanel.css.ts

@@ -1,8 +1,9 @@
 import { style } from '@vanilla-extract/css';
-import { config, toRem } from 'folds';
+import { config } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../../styles/sidePanel';
 
 export const WidgetsPanel = style({
-  width: toRem(360),
+  width: SIDE_PANEL_WIDTH,
   '@media': {
     '(max-width: 750px)': {
       position: 'fixed',

src/app/features/room/widgets/widgetUtils.test.ts

@@ -106,3 +106,19 @@ test('classifyWidgetCapabilities: reading protected state is fine, changing unpr
 test('loadWidgetConsent tolerates missing storage', () => {
   assert.equal(loadWidgetConsent('!r:x', 'w', 'https://w.example'), undefined);
 });
+
+test('[#266] space structure, call membership and Lotus room policy can never be granted', () => {
+  const { auto, ask } = classifyWidgetCapabilities(
+    [
+      'm.space.child',
+      'm.space.parent',
+      'org.matrix.msc3401.call',
+      'org.matrix.msc3401.call.member',
+      'm.call.member',
+      'io.lotus.voice_limit',
+      'io.lotus.room_quality',
+    ].map((t) => `org.matrix.msc2762.send.state_event:${t}`),
+  );
+  assert.equal(auto.size, 0);
+  assert.deepEqual(ask, []);
+});

src/app/features/room/widgets/widgetUtils.ts

@@ -67,6 +67,16 @@ export const PROTECTED_STATE_TYPES: ReadonlySet<string> = new Set([
   'm.room.third_party_invite',
   'im.vector.modular.widgets',
   'm.widget',
+  // [Gitea #266] Space structure, call membership and Lotus room policy: a
+  // widget could restructure a space, fake call membership or lift the
+  // voice-channel limit, so these can't be granted even with consent.
+  'm.space.child',
+  'm.space.parent',
+  'org.matrix.msc3401.call',
+  'org.matrix.msc3401.call.member',
+  'm.call.member',
+  'io.lotus.voice_limit',
+  'io.lotus.room_quality',
 ]);
 
 export type WidgetPermissionRequest = {
@@ -137,8 +147,11 @@ export const classifyWidgetCapabilities = (
  */
 export type StoredWidgetConsent = { url: string; allowed: Capability[]; denied: Capability[] };
 
+// [Gitea #266] Swept on logout by clearPlaintextCaches, so one account's
+// approvals never apply to the next account on the same device.
+export const WIDGET_CONSENT_PREFIX = 'lotus.widgetConsent.';
 export const widgetConsentKey = (roomId: string, widgetId: string): string =>
-  `lotus.widgetConsent.${roomId}.${widgetId}`;
+  `${WIDGET_CONSENT_PREFIX}${roomId}.${widgetId}`;
 
 export const loadWidgetConsent = (
   roomId: string,

src/app/pages/client/ClientRoot.tsx

@@ -33,6 +33,8 @@ import {
 } from '../../../client/initMatrix';
 import { deleteSearchCacheDatabase } from '../../utils/searchCache';
 import { clearPlaintextCaches } from '../../state/plaintextCaches';
+import { clearSoundboardClipCache } from '../../utils/soundboardClips';
+import { clearSharedPayload } from '../../../swShare';
 import { SplashScreen } from '../../components/splash-screen';
 import { ServerConfigsLoader } from '../../components/ServerConfigsLoader';
 import { CapabilitiesProvider } from '../../hooks/useCapabilities';
@@ -172,6 +174,10 @@ const useLogoutListener = (mx?: MatrixClient) => {
       // (translation, scheduled messages, recent searches/forwards/gifs/
       // stickers, nav paths) — wipe them on server-forced logout too.
       clearPlaintextCaches(mx?.getUserId() ?? undefined);
+      // [Gitea #57] As on manual logout: no decrypted clip bytes via blob: URLs.
+      clearSoundboardClipCache();
+      // [Gitea #267] As on manual logout: drop files stashed by the share target.
+      await clearSharedPayload().catch(() => undefined);
       // Remove only the session credential keys — NOT settings, drafts, and
       // other preferences (N98). The SDK's IndexedDB stores are cleared above;
       // window.localStorage.clear() is reserved for the explicit reset path.

src/app/pages/client/share/Share.tsx

@@ -145,6 +145,11 @@ export function Share() {
               <Box direction="Column" gap="400">
                 <Box direction="Column" gap="200">
                   <Text size="L400">Shared</Text>
+                  {/* [Gitea #267] Not everything that arrives here came from the
+                      user's share sheet; say so before they pick a room. */}
+                  <Text size="T200" priority="300">
+                    This came from another app or website. Check it before you send it.
+                  </Text>
                   {shared.files.map((f) => (
                     <Box key={f.name} alignItems="Center" gap="200">
                       <Icon

src/app/state/plaintextCaches.test.ts

@@ -26,7 +26,10 @@ const api = {
       : Object.getOwnPropertyDescriptor(target, key),
 });
 
-const { clearPlaintextCaches, plaintextCachesWiped } = await import('./plaintextCaches');
+const { clearPlaintextCaches, plaintextCachesWiped, WIDGET_CONSENT_KEY_PREFIX } =
+  await import('./plaintextCaches');
+const { WIDGET_CONSENT_PREFIX, widgetConsentKey } =
+  await import('../features/room/widgets/widgetUtils');
 
 test('clearPlaintextCaches removes every plaintext/PII localStorage key', () => {
   store.clear();
@@ -104,3 +107,17 @@ test('clearPlaintextCaches clears the encrypted-search opt-in and flags the wipe
   assert.equal(store.has('mxjssdk_memory_filter_FILTER_SYNC_@me:server'), false);
   assert.equal(plaintextCachesWiped(), true, 'draft writes stop until the page reloads');
 });
+
+test('[#266] clearPlaintextCaches sweeps remembered widget approvals', () => {
+  assert.equal(WIDGET_CONSENT_KEY_PREFIX, WIDGET_CONSENT_PREFIX, 'prefix kept in sync');
+  store.clear();
+  const consent = widgetConsentKey('!room:server', 'widget-1');
+  store.set(consent, '{"url":"https://pad.example","allowed":[],"denied":[]}');
+  store.set('lotus.widgetConsentNotAKey', 'kept');
+  removed.length = 0;
+
+  clearPlaintextCaches('@me:server');
+
+  assert.ok(removed.includes(consent), 'consent cleared');
+  assert.ok(store.has('lotus.widgetConsentNotAKey'), 'unrelated key kept');
+});

src/app/state/plaintextCaches.ts

@@ -139,6 +139,31 @@ const clearAccountScopedFlags = (userId?: string): void => {
   });
 };
 
+/**
+ * [Gitea #266] Remembered widget approvals (`lotus.widgetConsent.<room>.<widget>`,
+ * widgetUtils.ts) would otherwise apply silently to the next account on this
+ * device, and their keys list the previous account's rooms. Kept as a string
+ * here so logout doesn't pull the widget code into the entry chunk; a test
+ * checks it matches WIDGET_CONSENT_PREFIX.
+ */
+export const WIDGET_CONSENT_KEY_PREFIX = 'lotus.widgetConsent.';
+const clearWidgetConsents = (): void => {
+  let keys: string[];
+  try {
+    keys = Object.keys(localStorage);
+  } catch {
+    return;
+  }
+  keys.forEach((key) => {
+    if (!key.startsWith(WIDGET_CONSENT_KEY_PREFIX)) return;
+    try {
+      localStorage.removeItem(key);
+    } catch {
+      // best-effort
+    }
+  });
+};
+
 export const clearPlaintextCaches = (userId?: string): void => {
   wiped = true;
   clearTranslationCache();
@@ -153,5 +178,6 @@ export const clearPlaintextCaches = (userId?: string): void => {
   clearStatusMessage();
   clearCallVolumesAndSyncMeta(userId);
   clearAccountScopedFlags(userId);
+  clearWidgetConsents();
   if (userId) clearNavToActivePathStore(userId);
 };

src/app/styles/sidePanel.ts

@@ -0,0 +1,9 @@
+import { toRem } from 'folds';
+
+/**
+ * One width for every right-hand room panel (members, bookmarks, threads, a
+ * thread, media gallery, widgets). Swapping one panel for another must not
+ * resize the room view: when the widths differed, the header icons slid
+ * sideways and a second click on the same spot hit a different button (#263).
+ */
+export const SIDE_PANEL_WIDTH = toRem(340);

src/app/utils/topicMarkdown.test.ts

@@ -0,0 +1,72 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { buildTopicContent } from './topicMarkdown';
+
+test('a URL with underscores is sent verbatim (#262)', () => {
+  const t = 'Rules: https://wiki.lotusguild.org/en/server_rules_and_faq';
+  assert.deepEqual(buildTopicContent(t), { topic: t });
+});
+
+test('a markdown link keeps its underscored URL in both fields (#262)', () => {
+  const c = buildTopicContent('[Our wiki](https://wiki.example.org/my_cool_page)');
+  assert.ok('formatted_body' in c);
+  assert.match(c.formatted_body, /href="https:\/\/wiki\.example\.org\/my_cool_page"/);
+  assert.equal(c.topic, 'Our wiki (https://wiki.example.org/my_cool_page)');
+});
+
+test('room aliases and user IDs with underscores are untouched (#262)', () => {
+  for (const t of [
+    'Join #my_room_name:matrix.org',
+    'Ask @some_user_x:matrix.org',
+    'see snake_case_word',
+  ]) {
+    assert.deepEqual(buildTopicContent(t), { topic: t });
+  }
+});
+
+test('emphasis still works at word boundaries', () => {
+  const c = buildTopicContent('this is _really_ *great* and **bold**');
+  assert.ok('formatted_body' in c);
+  assert.match(c.formatted_body, /<i data-md="_">really<\/i>/);
+  assert.match(c.formatted_body, /<i data-md="\*">great<\/i>/);
+  assert.match(c.formatted_body, /<strong data-md="\*\*">bold<\/strong>/);
+  assert.equal(c.topic, 'this is really great and bold');
+});
+
+test('emphasis around an alias keeps the alias intact', () => {
+  const c = buildTopicContent('**Join #my_room:matrix.org**');
+  assert.ok('formatted_body' in c);
+  assert.match(c.formatted_body, /<strong data-md="\*\*">Join #my_room:matrix\.org<\/strong>/);
+  assert.equal(c.topic, 'Join #my_room:matrix.org');
+});
+
+test('inline code keeps its underscores and no backslashes appear', () => {
+  const c = buildTopicContent('run `a_b_c` now');
+  assert.ok('formatted_body' in c);
+  assert.match(c.formatted_body, /<code data-md="`">a_b_c<\/code>/);
+  assert.equal(c.topic, 'run a_b_c now');
+});
+
+test('a double quote in a link target cannot break out of the attribute (#262)', () => {
+  const c = buildTopicContent('[x](https://a" onclick="alert(1))');
+  assert.ok('formatted_body' in c);
+  assert.doesNotMatch(c.formatted_body, /" onclick="/);
+});
+
+test('HTML in the topic is escaped, and the plain topic shows it as typed', () => {
+  const c = buildTopicContent('**<b>hi</b> & bye**');
+  assert.ok('formatted_body' in c);
+  assert.match(c.formatted_body, /&lt;b&gt;hi&lt;\/b&gt; &amp; bye/);
+  assert.equal(c.topic, '<b>hi</b> & bye');
+});
+
+test('line breaks become <br> and survive in the plain topic', () => {
+  const c = buildTopicContent('**Rules**\nBe nice');
+  assert.ok('formatted_body' in c);
+  assert.equal(c.formatted_body, '<strong data-md="**">Rules</strong><br>Be nice');
+  assert.equal(c.topic, 'Rules\nBe nice');
+});
+
+test('plain text with no markdown is sent as typed', () => {
+  assert.deepEqual(buildTopicContent("It's <fun> & games"), { topic: "It's <fun> & games" });
+});

src/app/utils/topicMarkdown.ts

@@ -0,0 +1,63 @@
+import { parseInlineMD } from '../plugins/markdown';
+import { sanitizeText } from './sanitize';
+
+/**
+ * Room topic markdown → `m.room.topic` content (#262).
+ *
+ * Uses the composer's inline markdown parser (the same rules as messages: links,
+ * bare URLs and `"` are handled), with one topic-specific guard: an `_` between
+ * two letters/digits is literal, as in CommonMark. Topics are full of
+ * `#room_alias:server`, `@user_name:server` and snake_case paths, which the
+ * shared parser would otherwise turn into italics and, worse, drop from the
+ * plain `topic` that every other client shows.
+ */
+
+// Spans the guard must not touch: inline code, link targets, bare URLs.
+const PROTECTED = /(`[^`\n]*`|\]\([^)\n]*\)|https?:\/\/[^\s<>"]+)/;
+const INTRAWORD_UNDERSCORES = /(?<=[\p{L}\p{N}])_+(?=[\p{L}\p{N}])/gu;
+
+const escapeIntrawordUnderscores = (line: string): string =>
+  line
+    .split(PROTECTED)
+    .map((part, i) =>
+      // split() with one capture group puts the protected spans at odd indexes.
+      i % 2 === 1 ? part : part.replace(INTRAWORD_UNDERSCORES, (m) => m.replace(/_/g, '\\_')),
+    )
+    .join('');
+
+const ENTITIES: Record<string, string> = {
+  '&amp;': '&',
+  '&lt;': '<',
+  '&gt;': '>',
+  '&quot;': '"',
+  '&#39;': "'",
+};
+const decodeEntities = (s: string): string =>
+  s.replace(/&(?:amp|lt|gt|quot|#39);/g, (e) => ENTITIES[e]);
+
+/** Readable plain text for `topic`: markers dropped, links kept as "text (url)". */
+const htmlToPlain = (html: string): string =>
+  decodeEntities(
+    html
+      .replace(/<a\b[^>]*\bhref="([^"]*)"[^>]*>(.*?)<\/a>/g, (_m, href: string, label: string) => {
+        const text = label.replace(/<[^>]+>/g, '');
+        return text === href ? href : `${text} (${href})`;
+      })
+      .replace(/<br>/g, '\n')
+      .replace(/<[^>]+>/g, ''),
+  );
+
+export type TopicContent =
+  | { topic: string }
+  | { topic: string; format: 'org.matrix.custom.html'; formatted_body: string };
+
+export function buildTopicContent(text: string): TopicContent {
+  const lines = text.split('\n');
+  const html = lines
+    .map((line) => parseInlineMD(sanitizeText(escapeIntrawordUnderscores(line))))
+    .join('<br>');
+  const plainHtml = lines.map(sanitizeText).join('<br>');
+  // No markdown at all: send the text as typed, without a formatted body.
+  if (html === plainHtml) return { topic: text };
+  return { topic: htmlToPlain(html), format: 'org.matrix.custom.html', formatted_body: html };
+}

src/client/initMatrix.ts

@@ -9,6 +9,7 @@ import { pushSessionToSW } from '../sw-session';
 import { deleteSearchCacheDatabase, shouldRunBootCleanup } from '../app/utils/searchCache';
 import { clearPlaintextCaches } from '../app/state/plaintextCaches';
 import { clearSoundboardClipCache } from '../app/utils/soundboardClips';
+import { clearSharedPayload } from '../swShare';
 
 // Thrown when the local IndexedDB has a higher schema version than this SDK expects.
 // This happens after a downgrade (e.g. matrix-js-sdk was briefly upgraded and then reverted).
@@ -146,6 +147,9 @@ export const logoutClient = async (mx: MatrixClient) => {
   // [Gitea #57] Same reasoning as clearPlaintextCaches: decrypted soundboard
   // clip bytes stay reachable via live blob: URLs until the reload otherwise.
   clearSoundboardClipCache();
+  // [Gitea #267] Files stashed by the share target stay in Cache Storage until
+  // /share is opened; a shared photo must not outlive the logout.
+  await clearSharedPayload().catch(() => undefined);
   // Remove only the session credential keys, preserving user preferences and
   // unsent drafts (N98). The factory-reset path is clearLoginData() below.
   removeFallbackSession();

src/sw.ts

@@ -1,7 +1,7 @@
 /// <reference lib="WebWorker" />
 
 import { precacheAndRoute, type PrecacheEntry } from 'workbox-precaching';
-import { SHARE_TARGET_PATH, stashSharedForm } from './swShare';
+import { isTrustedShareRequest, SHARE_TARGET_PATH, stashSharedForm } from './swShare';
 import { pickReplySession, replyFailureText, sendNotificationReply } from './swReply';
 
 export type {};
@@ -249,6 +249,11 @@ self.addEventListener('fetch', (event: FetchEvent) => {
   // share_target). Stash the form and bounce to the in-app /share page.
   if (method === 'POST' && new URL(url).pathname.endsWith(SHARE_TARGET_PATH)) {
     const base = new URL(url).pathname.slice(0, -SHARE_TARGET_PATH.length);
+    // [Gitea #267] A cross-site form posting here is not a share: drop it.
+    if (!isTrustedShareRequest(event.request.headers, self.location.origin)) {
+      event.respondWith(Response.redirect(`${base}/`, 303));
+      return;
+    }
     event.respondWith(
       stashSharedForm(event.request, base).catch(() => Response.redirect(`${base}/`, 303)),
     );

src/swShare.test.ts

@@ -1,6 +1,6 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { shareDraftText } from './swShare';
+import { isTrustedShareRequest, shareDraftText } from './swShare';
 
 const base = { files: [], receivedAt: 0 };
 
@@ -25,3 +25,14 @@ test('shareDraftText drops a title/url the text already contains', () => {
   assert.equal(shareDraftText({ ...base, url: 'https://x.test' }), 'https://x.test');
   assert.equal(shareDraftText(base), '');
 });
+
+test('[#267] a share another website submitted is refused', () => {
+  const app = 'https://chat.lotusguild.org';
+  const h = (origin?: string) => new Headers(origin ? { Origin: origin } : {});
+  assert.equal(isTrustedShareRequest(h(), app), true, 'no Origin (OS share sheet)');
+  assert.equal(isTrustedShareRequest(h('null'), app), true, 'opaque origin (OS share sheet)');
+  assert.equal(isTrustedShareRequest(h(app), app), true, 'the app itself');
+  assert.equal(isTrustedShareRequest(h('https://evil.example'), app), false);
+  assert.equal(isTrustedShareRequest(h('https://chat.lotusguild.org.evil.example'), app), false);
+  assert.equal(isTrustedShareRequest(h('http://chat.lotusguild.org'), app), false, 'other scheme');
+});

src/swShare.ts

@@ -20,6 +20,27 @@ export type SharePayload = {
   receivedAt: number;
 };
 
+/**
+ * [Gitea #267] Refuse a share that another website submitted: any site could
+ * otherwise auto-submit a cross-site form here and drop attacker-chosen text
+ * and files into the "Share to…" picker as if the user had shared them.
+ *
+ * The worker can't use `Sec-Fetch-Site`: fetch-metadata headers are added
+ * after the service worker and never appear on `event.request` (checked in
+ * Chromium). `Origin` does: a cross-site form carries the site's origin. The
+ * OS share sheet's POST has no web initiator, so its Origin is `null` or
+ * absent, and both stay accepted. A page can also produce `Origin: null`
+ * (sandboxed frame, no-referrer), which is why /share also says the content
+ * came from elsewhere.
+ */
+export const isTrustedShareRequest = (
+  headers: Pick<Headers, 'get'>,
+  selfOrigin: string,
+): boolean => {
+  const origin = headers.get('Origin');
+  return origin === null || origin === 'null' || origin === selfOrigin;
+};
+
 /** Worker side: stash the POSTed form and answer with a redirect to /share. */
 export async function stashSharedForm(request: Request, base: string): Promise<Response> {
   const form = await request.formData();