fix: restrict shared chat file access to require valid share_id

Previously, any authenticated user could access files attached to any
shared chat by guessing the file UUID. The has_access_to_file function
granted access if a file appeared in ANY shared chat, without verifying
the requester had legitimate access to that specific share.

Backend: has_access_to_file now requires either chat ownership or a
matching share_id to grant shared-chat file access. All file endpoints
accept an optional share_id query parameter.

Frontend: A shareId store is set when viewing a shared chat (/s/{id})
and cleared on navigation away. Markdown components and the token
replacement utility append ?share_id= to file content URLs when set,
enabling authorized file access for shared chat viewers.

backend/open_webui/routers/files.py

@@ -412,7 +412,12 @@ async def delete_all_files(user=Depends(get_admin_user), db: Session = Depends(g
 
 
 @router.get('/{id}', response_model=Optional[FileModel])
-async def get_file_by_id(id: str, user=Depends(get_verified_user), db: Session = Depends(get_session)):
+async def get_file_by_id(
+    id: str,
+    share_id: Optional[str] = Query(None),
+    user=Depends(get_verified_user),
+    db: Session = Depends(get_session),
+):
     file = Files.get_file_by_id(id, db=db)
 
     if not file:
@@ -421,7 +426,7 @@ async def get_file_by_id(id: str, user=Depends(get_verified_user), db: Session =
             detail=ERROR_MESSAGES.NOT_FOUND,
         )
 
-    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, db=db):
+    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, share_id=share_id, db=db):
         return file
     else:
         raise HTTPException(
@@ -434,6 +439,7 @@ async def get_file_by_id(id: str, user=Depends(get_verified_user), db: Session =
 async def get_file_process_status(
     id: str,
     stream: bool = Query(False),
+    share_id: Optional[str] = Query(None),
     user=Depends(get_verified_user),
     db: Session = Depends(get_session),
 ):
@@ -445,7 +451,7 @@ async def get_file_process_status(
             detail=ERROR_MESSAGES.NOT_FOUND,
         )
 
-    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, db=db):
+    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, share_id=share_id, db=db):
         if stream:
             MAX_FILE_PROCESSING_DURATION = 3600 * 2
 
@@ -495,7 +501,12 @@ async def get_file_process_status(
 
 
 @router.get('/{id}/data/content')
-async def get_file_data_content_by_id(id: str, user=Depends(get_verified_user), db: Session = Depends(get_session)):
+async def get_file_data_content_by_id(
+    id: str,
+    share_id: Optional[str] = Query(None),
+    user=Depends(get_verified_user),
+    db: Session = Depends(get_session),
+):
     file = Files.get_file_by_id(id, db=db)
 
     if not file:
@@ -504,7 +515,7 @@ async def get_file_data_content_by_id(id: str, user=Depends(get_verified_user),
             detail=ERROR_MESSAGES.NOT_FOUND,
         )
 
-    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, db=db):
+    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, share_id=share_id, db=db):
         return {'content': file.data.get('content', '')}
     else:
         raise HTTPException(
@@ -587,6 +598,7 @@ async def get_file_content_by_id(
     id: str,
     user=Depends(get_verified_user),
     attachment: bool = Query(False),
+    share_id: Optional[str] = Query(None),
     db: Session = Depends(get_session),
 ):
     file = Files.get_file_by_id(id, db=db)
@@ -597,7 +609,7 @@ async def get_file_content_by_id(
             detail=ERROR_MESSAGES.NOT_FOUND,
         )
 
-    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, db=db):
+    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, share_id=share_id, db=db):
         try:
             file_path = Storage.get_file(file.path)
             file_path = Path(file_path)
@@ -646,7 +658,12 @@ async def get_file_content_by_id(
 
 
 @router.get('/{id}/content/html')
-async def get_html_file_content_by_id(id: str, user=Depends(get_verified_user), db: Session = Depends(get_session)):
+async def get_html_file_content_by_id(
+    id: str,
+    share_id: Optional[str] = Query(None),
+    user=Depends(get_verified_user),
+    db: Session = Depends(get_session),
+):
     file = Files.get_file_by_id(id, db=db)
 
     if not file:
@@ -662,7 +679,7 @@ async def get_html_file_content_by_id(id: str, user=Depends(get_verified_user),
             detail=ERROR_MESSAGES.NOT_FOUND,
         )
 
-    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, db=db):
+    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, share_id=share_id, db=db):
         try:
             file_path = Storage.get_file(file.path)
             file_path = Path(file_path)
@@ -693,7 +710,12 @@ async def get_html_file_content_by_id(id: str, user=Depends(get_verified_user),
 
 
 @router.get('/{id}/content/{file_name}')
-async def get_file_content_by_id(id: str, user=Depends(get_verified_user), db: Session = Depends(get_session)):
+async def get_file_content_by_id(
+    id: str,
+    share_id: Optional[str] = Query(None),
+    user=Depends(get_verified_user),
+    db: Session = Depends(get_session),
+):
     file = Files.get_file_by_id(id, db=db)
 
     if not file:
@@ -702,7 +724,7 @@ async def get_file_content_by_id(id: str, user=Depends(get_verified_user), db: S
             detail=ERROR_MESSAGES.NOT_FOUND,
         )
 
-    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, db=db):
+    if file.user_id == user.id or user.role == 'admin' or has_access_to_file(id, 'read', user, share_id=share_id, db=db):
         file_path = file.path
 
         # Handle Unicode filenames

backend/open_webui/utils/access_control/files.py

@@ -18,6 +18,7 @@ def has_access_to_file(
     file_id: str | None,
     access_type: str,
     user: UserModel,
+    share_id: str | None = None,
     db: Session | None = None,
 ) -> bool:
     """
@@ -25,7 +26,7 @@ def has_access_to_file(
     - Knowledge bases (ownership or access grants)
     - Shared workspace models that attach the file directly
     - Channels the user is a member of
-    - Shared chats
+    - Shared chats (requires valid share_id or chat ownership)
 
     NOTE: This does NOT check direct file ownership — callers should check
     file.user_id == user.id separately before calling this.
@@ -65,11 +66,17 @@ def has_access_to_file(
     if access_type == 'read' and channels:
         return True
 
-    # Check if the file is associated with any chats the user has access to
-    # TODO: Granular access control for chats
+    # Check if the file is associated with any shared chats the user can access.
+    # Access is granted only when:
+    #   1. The caller provides a valid share_id that matches a shared chat
+    #      containing this file (proves they have the share link), OR
+    #   2. The caller owns the shared chat containing this file.
     chats = Chats.get_shared_chats_by_file_id(file_id, db=db)
-    if chats:
-        return True
+    for chat in chats:
+        if chat.user_id == user.id:
+            return True
+        if share_id and access_type == 'read' and chat.share_id == share_id:
+            return True
 
     # Check if the file is directly attached to a shared workspace model
     for model in Models.get_models_by_user_id(user.id, permission=access_type, db=db):

src/lib/components/chat/Messages/Markdown/HTMLToken.svelte

@@ -3,7 +3,7 @@
 	import type { Token } from 'marked';
 
 	import { WEBUI_BASE_URL } from '$lib/constants';
-	import { settings } from '$lib/stores';
+	import { settings, shareId } from '$lib/stores';
 
 	export let id: string;
 	export let token: Token;
@@ -109,7 +109,7 @@
 		{#if fileId}
 			<iframe
 				class="w-full my-2"
-				src={`${WEBUI_BASE_URL}/api/v1/files/${fileId}/content/html`}
+				src={`${WEBUI_BASE_URL}/api/v1/files/${fileId}/content/html${$shareId ? `?share_id=${encodeURIComponent($shareId)}` : ''}`}
 				title="Content"
 				frameborder="0"
 				sandbox="allow-scripts allow-downloads{($settings?.iframeSandboxAllowForms ?? false)

src/lib/components/chat/Messages/Markdown/MarkdownInlineTokens.svelte

@@ -9,6 +9,7 @@
 	const i18n = getContext('i18n');
 
 	import { WEBUI_BASE_URL } from '$lib/constants';
+	import { shareId } from '$lib/stores';
 	import { copyToClipboard, unescapeHtml } from '$lib/utils';
 
 	import Image from '$lib/components/common/Image.svelte';
@@ -113,7 +114,7 @@
 		{/if}
 	{:else if token.type === 'iframe'}
 		<iframe
-			src="{WEBUI_BASE_URL}/api/v1/files/{token.fileId}/content"
+			src="{WEBUI_BASE_URL}/api/v1/files/{token.fileId}/content{$shareId ? `?share_id=${encodeURIComponent($shareId)}` : ''}"
 			title={token.fileId}
 			width="100%"
 			frameborder="0"

src/lib/components/chat/Messages/Markdown/MarkdownTokens.svelte

@@ -10,7 +10,7 @@
 	import { copyToClipboard, unescapeHtml } from '$lib/utils';
 
 	import { WEBUI_BASE_URL } from '$lib/constants';
-	import { settings } from '$lib/stores';
+	import { settings, shareId } from '$lib/stores';
 
 	import CodeBlock from '$lib/components/chat/Messages/CodeBlock.svelte';
 	import MarkdownInlineTokens from '$lib/components/chat/Messages/Markdown/MarkdownInlineTokens.svelte';
@@ -468,7 +468,7 @@
 		<HtmlToken {id} {token} {onSourceClick} />
 	{:else if token.type === 'iframe'}
 		<iframe
-			src="{WEBUI_BASE_URL}/api/v1/files/{token.fileId}/content"
+			src="{WEBUI_BASE_URL}/api/v1/files/{token.fileId}/content{$shareId ? `?share_id=${encodeURIComponent($shareId)}` : ''}"
 			title={token.fileId}
 			width="100%"
 			frameborder="0"

src/lib/components/common/Image.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
 	import { WEBUI_BASE_URL } from '$lib/constants';
 
-	import { settings } from '$lib/stores';
+	import { settings, shareId } from '$lib/stores';
 	import ImagePreview from './ImagePreview.svelte';
 	import XMark from '$lib/components/icons/XMark.svelte';
 	import { getContext } from 'svelte';
@@ -19,7 +19,14 @@
 	const i18n = getContext('i18n');
 
 	let _src = '';
-	$: _src = src.startsWith('/') ? `${WEBUI_BASE_URL}${src}` : src;
+	$: {
+		let resolved = src.startsWith('/') ? `${WEBUI_BASE_URL}${src}` : src;
+		if ($shareId && resolved.includes('/api/v1/files/') && resolved.includes('/content')) {
+			const separator = resolved.includes('?') ? '&' : '?';
+			resolved = `${resolved}${separator}share_id=${encodeURIComponent($shareId)}`;
+		}
+		_src = resolved;
+	}
 
 	let showImagePreview = false;
 </script>

src/lib/stores/index.ts

@@ -52,6 +52,7 @@ export const shortCodesToEmojis = writable(
 export const TTSWorker = writable(null);
 
 export const chatId = writable('');
+export const shareId: Writable<string | null> = writable(null);
 export const chatTitle = writable('');
 
 export const channels = writable([]);

src/lib/utils/index.ts

@@ -2,6 +2,8 @@ import type { Writable } from 'svelte/store';
 import { v4 as uuidv4 } from 'uuid';
 import sha256 from 'js-sha256';
 import { WEBUI_BASE_URL } from '$lib/constants';
+import { shareId } from '$lib/stores';
+import { get } from 'svelte/store';
 
 import dayjs from 'dayjs';
 import relativeTime from 'dayjs/plugin/relativeTime';
@@ -59,8 +61,11 @@ export const replaceTokens = (content, char, user) => {
 		{ regex: /{{user}}/gi, replacement: user },
 		{
 			regex: /{{VIDEO_FILE_ID_([a-f0-9-]+)}}/gi,
-			replacement: (_, fileId) =>
-				`<video src="${WEBUI_BASE_URL}/api/v1/files/${fileId}/content" controls></video>`
+			replacement: (_, fileId) => {
+				const sid = get(shareId);
+				const query = sid ? `?share_id=${encodeURIComponent(sid)}` : '';
+				return `<video src="${WEBUI_BASE_URL}/api/v1/files/${fileId}/content${query}" controls></video>`;
+			}
 		},
 		{
 			regex: /{{HTML_FILE_ID_([a-f0-9-]+)}}/gi,

src/routes/s/[id]/+page.svelte

@@ -1,11 +1,11 @@
 <script lang="ts">
-	import { onMount, tick, getContext } from 'svelte';
+	import { onMount, onDestroy, tick, getContext } from 'svelte';
 	import { goto } from '$app/navigation';
 	import { page } from '$app/stores';
 
 	import dayjs from 'dayjs';
 
-	import { settings, chatId, WEBUI_NAME, models, config } from '$lib/stores';
+	import { settings, chatId, shareId, WEBUI_NAME, models, config } from '$lib/stores';
 	import { convertMessagesToHistory, createMessagesList } from '$lib/utils';
 
 	import { getChatByShareId, cloneSharedChatById } from '$lib/apis/chats';
@@ -86,6 +86,7 @@
 			)
 		);
 		await chatId.set($page.params.id);
+		await shareId.set($page.params.id);
 		chat = await getChatByShareId(localStorage.token, $chatId).catch(async (error) => {
 			await goto('/');
 			return null;
@@ -139,6 +140,10 @@
 			goto(`/c/${res.id}`);
 		}
 	};
+
+	onDestroy(() => {
+		shareId.set(null);
+	});
 </script>
 
 <svelte:head>