fix(a11y): axe findings: dialog names, aria-pressed, labels, avatar alt, placeholder contrast (#278)

- Modal500 takes a label: Room/Space Settings ("<name> settings") and
  Settings dialogs have accessible names.
- aria-selected on plain buttons (inbox filter chips, date/time picker
  chips, verification/usage/notification menu items) -> aria-pressed; the
  Permissions power chips open a menu -> aria-haspopup + aria-expanded.
- Labels tied to the room pack name input and the Export From/To dates.
- UserAvatar defaults to alt="" (decorative next to a name / in a
  labelled button) unless a caller passes one.
- Composer placeholder: Slate's inline opacity 0.333 overrode the #222
  AA-contrast class (2.66:1); it is dropped so the class (0.75) applies.
- e2e/a11y.spec.ts also audits Room Settings → Permissions, Emojis &
  Stickers and Export, checks the dialog name, and audits the inbox.

Fixes #278

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

e2e/a11y.spec.ts

@@ -118,8 +118,26 @@ test.describe('accessibility', () => {
     test('room settings', async ({ page }) => {
       await page.getByRole('button', { name: 'More Options' }).first().click();
       await page.getByText('Room Settings', { exact: true }).click();
-      await expect(page.getByRole('dialog').first()).toBeVisible();
+      // [Gitea #278] The dialog has an accessible name.
+      await expect(page.getByRole('dialog', { name: 'A11y Room settings' })).toBeVisible();
       await auditPage(page, 'room settings');
+      // [Gitea #278] aria-selected on the power chips, unlabelled pack name and
+      // export date inputs were only on these pages.
+      // One page at a time, in order.
+      for (const name of ['Permissions', 'Emojis & Stickers', 'Export']) {
+        // eslint-disable-next-line no-await-in-loop
+        await page.getByRole('dialog').getByText(name, { exact: true }).first().click();
+        // eslint-disable-next-line no-await-in-loop
+        await page.waitForTimeout(1000);
+        // eslint-disable-next-line no-await-in-loop
+        await auditPage(page, `room settings: ${name}`);
+      }
+    });
+
+    test('inbox invites', async ({ page }) => {
+      await page.goto('/inbox/invites/');
+      await expect(page.getByRole('button', { name: /Known|Unknown|Spam/ }).first()).toBeVisible();
+      await auditPage(page, 'inbox invites');
     });
   });
 });

src/app/components/ManualVerification.tsx

@@ -82,7 +82,7 @@ export function ManualVerificationMethodSwitcher({
                 <MenuItem
                   size="300"
                   variant="Surface"
-                  aria-selected={value === ManualVerificationMethod.RecoveryPassphrase}
+                  aria-pressed={value === ManualVerificationMethod.RecoveryPassphrase}
                   radii="300"
                   onClick={() => handleSelect(ManualVerificationMethod.RecoveryPassphrase)}
                 >
@@ -93,7 +93,7 @@ export function ManualVerificationMethodSwitcher({
                 <MenuItem
                   size="300"
                   variant="Surface"
-                  aria-selected={value === ManualVerificationMethod.RecoveryKey}
+                  aria-pressed={value === ManualVerificationMethod.RecoveryKey}
                   radii="300"
                   onClick={() => handleSelect(ManualVerificationMethod.RecoveryKey)}
                 >

src/app/components/Modal500.tsx

@@ -7,8 +7,10 @@ import { ScreenSize, useScreenSizeContext } from '../hooks/useScreenSize';
 type Modal500Props = {
   requestClose: () => void;
   children: ReactNode;
+  /** [Gitea #278] The dialog's accessible name (role="dialog" needs one). */
+  label: string;
 };
-export function Modal500({ requestClose, children }: Modal500Props) {
+export function Modal500({ requestClose, children, label }: Modal500Props) {
   const isMobile = useScreenSizeContext() === ScreenSize.Mobile;
   return (
     <Overlay open backdrop={<OverlayBackdrop />}>
@@ -26,6 +28,7 @@ export function Modal500({ requestClose, children }: Modal500Props) {
             variant="Background"
             role="dialog"
             aria-modal="true"
+            aria-label={label}
             // On mobile expand to fill the viewport. On desktop fall back to the
             // folds `size="500"` width (~50rem) — overriding maxWidth here would
             // squish the two-pane settings layout.

src/app/components/editor/Editor.tsx

@@ -117,7 +117,14 @@ export const CustomEditor = forwardRef<HTMLDivElement, CustomEditorProps>(
 
     const renderPlaceholder = useCallback(
       ({ attributes, children }: RenderPlaceholderProps) => (
-        <span {...attributes} className={css.EditorPlaceholderContainer}>
+        <span
+          {...attributes}
+          // [Gitea #278] Slate puts an inline `opacity: 0.333` on the placeholder,
+          // which beat EditorPlaceholderContainer's AA-contrast opacity (#222):
+          // measured 2.66:1. Drop it so the class decides.
+          style={{ ...attributes.style, opacity: undefined }}
+          className={css.EditorPlaceholderContainer}
+        >
           {/* Inner component to style the actual text position and appearance */}
           <Text as="span" className={css.EditorPlaceholderTextVisual} truncate>
             {children}

src/app/components/image-pack-view/UsageSwitcher.tsx

@@ -39,7 +39,7 @@ export function UsageSelector({ selected, onChange }: UsageSelectorProps) {
           key={getUsageStr(usage)}
           size="300"
           variant={isSelected(usage) ? 'SurfaceVariant' : 'Surface'}
-          aria-selected={isSelected(usage)}
+          aria-pressed={isSelected(usage)}
           radii="300"
           onClick={() => onChange(usage)}
         >

src/app/components/time-date/DatePicker.tsx

@@ -69,7 +69,7 @@ export const DatePicker = forwardRef<HTMLDivElement, DatePickerProps>(
                   variant={selectedDay === day ? 'Primary' : 'SurfaceVariant'}
                   fill="None"
                   radii="300"
-                  aria-selected={selectedDay === day}
+                  aria-pressed={selectedDay === day}
                   onClick={() => handleDay(day)}
                   disabled={
                     (selectedYear === minYear && selectedMonth === minMonth && day < minDay) ||
@@ -90,7 +90,7 @@ export const DatePicker = forwardRef<HTMLDivElement, DatePickerProps>(
                   variant={selectedMonth === month ? 'Primary' : 'SurfaceVariant'}
                   fill="None"
                   radii="300"
-                  aria-selected={selectedMonth === month}
+                  aria-pressed={selectedMonth === month}
                   onClick={() => handleMonth(month)}
                   disabled={
                     (selectedYear === minYear && month < minMonth) ||
@@ -115,7 +115,7 @@ export const DatePicker = forwardRef<HTMLDivElement, DatePickerProps>(
                   variant={selectedYear === year ? 'Primary' : 'SurfaceVariant'}
                   fill="None"
                   radii="300"
-                  aria-selected={selectedYear === year}
+                  aria-pressed={selectedYear === year}
                   onClick={() => handleYear(year)}
                 >
                   <Text size="T300">{year}</Text>

src/app/components/time-date/TimePicker.tsx

@@ -71,7 +71,7 @@ export const TimePicker = forwardRef<HTMLDivElement, TimePickerProps>(
                     variant={hour === selectedHour ? 'Primary' : 'Background'}
                     fill="None"
                     radii="300"
-                    aria-selected={hour === selectedHour}
+                    aria-pressed={hour === selectedHour}
                     onClick={() => handleHour(hour)}
                     disabled={(minDay && hour < minHour24) || (maxDay && hour > maxHour24)}
                   >
@@ -90,7 +90,7 @@ export const TimePicker = forwardRef<HTMLDivElement, TimePickerProps>(
                       variant={hour === selectedHour ? 'Primary' : 'Background'}
                       fill="None"
                       radii="300"
-                      aria-selected={hour === selectedHour}
+                      aria-pressed={hour === selectedHour}
                       onClick={() => handleHour(hour)}
                       disabled={
                         (minDay && hour12to24(hour, selectedPM) < minHour24) ||
@@ -109,7 +109,7 @@ export const TimePicker = forwardRef<HTMLDivElement, TimePickerProps>(
                 variant={minute === selectedMinute ? 'Primary' : 'Background'}
                 fill="None"
                 radii="300"
-                aria-selected={minute === selectedMinute}
+                aria-pressed={minute === selectedMinute}
                 onClick={() => handleMinute(minute)}
                 disabled={
                   (minDay && hour24 === minHour24 && minute < minMinute) ||
@@ -127,7 +127,7 @@ export const TimePicker = forwardRef<HTMLDivElement, TimePickerProps>(
                 variant={!selectedPM ? 'Primary' : 'SurfaceVariant'}
                 fill="None"
                 radii="300"
-                aria-selected={!selectedPM}
+                aria-pressed={!selectedPM}
                 onClick={() => handlePeriod(false)}
                 disabled={minDay && minPM}
               >
@@ -138,7 +138,7 @@ export const TimePicker = forwardRef<HTMLDivElement, TimePickerProps>(
                 variant={selectedPM ? 'Primary' : 'SurfaceVariant'}
                 fill="None"
                 radii="300"
-                aria-selected={selectedPM}
+                aria-pressed={selectedPM}
                 onClick={() => handlePeriod(true)}
                 disabled={maxDay && !maxPM}
               >

src/app/components/user-avatar/UserAvatar.tsx

@@ -33,7 +33,9 @@ export function UserAvatar({ className, userId, src, alt, renderFallback }: User
     <AvatarImage
       className={classNames(css.UserAvatar, className)}
       src={src}
-      alt={alt}
+      // [Gitea #278] An avatar sits next to the person's name or inside a
+      // labelled button, so without an explicit alt it is decorative.
+      alt={alt ?? ''}
       onError={() => setError(true)}
       onLoad={handleLoad}
       draggable={false}

src/app/features/common-settings/emojis-stickers/RoomPacks.tsx

@@ -109,8 +109,11 @@ function CreatePackTile({ packs, roomId }: CreatePackTileProps) {
           alignItems="End"
         >
           <Box direction="Column" gap="100" grow="Yes">
-            <Text size="L400">Name</Text>
+            <Text as="label" htmlFor="room-pack-name" size="L400">
+              Name
+            </Text>
             <Input
+              id="room-pack-name"
               name="nameInput"
               required
               size="400"

src/app/features/common-settings/permissions/PermissionGroups.tsx

@@ -136,7 +136,8 @@ export function PermissionGroups({
                     outlined={powerChanges}
                     fill="Soft"
                     radii="Pill"
-                    aria-selected={opened}
+                    aria-haspopup="menu"
+                    aria-expanded={opened}
                     disabled={!canEdit || applyingChanges}
                     after={
                       powerChanges && (
@@ -200,7 +201,8 @@ export function PermissionGroups({
                           outlined={powerChanges}
                           fill="Soft"
                           radii="Pill"
-                          aria-selected={opened}
+                          aria-haspopup="menu"
+                          aria-expanded={opened}
                           disabled={!canEdit || applyingChanges}
                           after={
                             powerChanges && (

src/app/features/room-settings/ExportRoomHistory.tsx

@@ -353,8 +353,11 @@ ${msgRows}
                 >
                   <Box gap="400" wrap="Wrap">
                     <Box direction="Column" gap="100" style={{ flex: 1, minWidth: 160 }}>
-                      <Text size="T300">From</Text>
+                      <Text as="label" htmlFor="export-from-date" size="T300">
+                        From
+                      </Text>
                       <Input
+                        id="export-from-date"
                         type="date"
                         variant="Secondary"
                         size="400"
@@ -364,8 +367,11 @@ ${msgRows}
                       />
                     </Box>
                     <Box direction="Column" gap="100" style={{ flex: 1, minWidth: 160 }}>
-                      <Text size="T300">To</Text>
+                      <Text as="label" htmlFor="export-to-date" size="T300">
+                        To
+                      </Text>
                       <Input
+                        id="export-to-date"
                         type="date"
                         variant="Secondary"
                         size="400"

src/app/features/room-settings/RoomSettingsRenderer.tsx

@@ -21,7 +21,7 @@ function RenderSettings({ state }: RenderSettingsProps) {
   if (!room) return null;
 
   return (
-    <Modal500 requestClose={closeSettings}>
+    <Modal500 requestClose={closeSettings} label={`${room.name} settings`}>
       <SpaceProvider value={space ?? null}>
         <RoomProvider value={room}>
           <RoomSettings initialPage={page} requestClose={closeSettings} />

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/features/settings/notifications/NotificationModeSwitcher.tsx

@@ -98,7 +98,7 @@ export function NotificationModeSwitcher({ pushRule, onChange }: NotificationMod
                     key={mode}
                     size="300"
                     variant="Surface"
-                    aria-selected={mode === selectedMode}
+                    aria-pressed={mode === selectedMode}
                     radii="300"
                     onClick={() => handleSelect(mode)}
                   >

src/app/features/space-settings/SpaceSettingsRenderer.tsx

@@ -21,7 +21,7 @@ function RenderSettings({ state }: RenderSettingsProps) {
   if (!room) return null;
 
   return (
-    <Modal500 requestClose={closeSettings}>
+    <Modal500 requestClose={closeSettings} label={`${room.name} space settings`}>
       <SpaceProvider value={space ?? null}>
         <RoomProvider value={room}>
           <SpaceSettings initialPage={page} requestClose={closeSettings} />

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/inbox/Invites.tsx

@@ -369,7 +369,7 @@ function InviteFilters({
     <Box gap="200">
       <Chip
         variant={isKnown ? 'Success' : 'Surface'}
-        aria-selected={isKnown}
+        aria-pressed={isKnown}
         outlined={!isKnown}
         onClick={() => onFilter(InviteFilter.Known)}
         before={isKnown && <Icon size="100" src={Icons.Check} />}
@@ -385,7 +385,7 @@ function InviteFilters({
       </Chip>
       <Chip
         variant={isUnknown ? 'Warning' : 'Surface'}
-        aria-selected={isUnknown}
+        aria-pressed={isUnknown}
         outlined={!isUnknown}
         onClick={() => onFilter(InviteFilter.Unknown)}
         before={isUnknown && <Icon size="100" src={Icons.Check} />}
@@ -401,7 +401,7 @@ function InviteFilters({
       </Chip>
       <Chip
         variant={isSpam ? 'Critical' : 'Surface'}
-        aria-selected={isSpam}
+        aria-pressed={isSpam}
         outlined={!isSpam}
         onClick={() => onFilter(InviteFilter.Spam)}
         before={isSpam && <Icon size="100" src={Icons.Check} />}

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/pages/client/sidebar/SettingsTab.tsx

@@ -217,7 +217,7 @@ export function SettingsTab() {
       </SidebarItemTooltip>
       <PresencePicker />
       {settingsOpen && (
-        <Modal500 requestClose={() => setSettingsOpen(false)}>
+        <Modal500 requestClose={() => setSettingsOpen(false)} label="Settings">
           <Settings initialPage={initialPage} requestClose={() => setSettingsOpen(false)} />
         </Modal500>
       )}

src/app/pages/client/sidebar/UnverifiedTab.tsx

@@ -82,7 +82,7 @@ function UnverifiedIndicator() {
         </SidebarItem>
       )}
       {settings && (
-        <Modal500 requestClose={closeSettings}>
+        <Modal500 requestClose={closeSettings} label="Settings">
           <Settings initialPage={SettingsPages.DevicesPage} requestClose={closeSettings} />
         </Modal500>
       )}

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/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();