Fix for CVE-2024-47779 / GHSA-3jm3-x98c-r34x

src/serviceworker/index.ts

@@ -40,12 +40,15 @@ global.addEventListener("fetch", (event: FetchEvent) => {
 
     // Note: ideally we'd keep the request headers etc, but in practice we can't even see those details.
     // See https://stackoverflow.com/a/59152482
-    let url = event.request.url;
+    const url = new URL(event.request.url);
 
     // We only intercept v3 download and thumbnail requests as presumably everything else is deliberate.
     // For example, `/_matrix/media/unstable` or `/_matrix/media/v3/preview_url` are something well within
     // the control of the application, and appear to be choices made at a higher level than us.
-    if (!url.includes("/_matrix/media/v3/download") && !url.includes("/_matrix/media/v3/thumbnail")) {
+    if (
+        !url.pathname.startsWith("/_matrix/media/v3/download") &&
+        !url.pathname.startsWith("/_matrix/media/v3/thumbnail")
+    ) {
         return; // not a URL we care about
     }
 
@@ -53,34 +56,42 @@ global.addEventListener("fetch", (event: FetchEvent) => {
     // later on we need to proxy the request through if it turns out the server doesn't support authentication.
     event.respondWith(
         (async (): Promise<Response> => {
-            let accessToken: string | undefined;
+            let auth: { accessToken?: string; homeserver: string } | undefined;
             try {
                 // Figure out which homeserver we're communicating with
-                const csApi = url.substring(0, url.indexOf("/_matrix/media/v3"));
+                const csApi = url.origin;
 
                 // Add jitter to reduce request spam, particularly to `/versions` on initial page load
                 await new Promise<void>((resolve) => setTimeout(() => resolve(), Math.random() * 10));
 
-                // Locate our access token, and populate the fetchConfig with the authentication header.
+                // Locate the access token and homeserver url
                 // @ts-expect-error - service worker types are not available. See 'fetch' event handler.
                 const client = await global.clients.get(event.clientId);
-                accessToken = await getAccessToken(client);
+                auth = await getAuthData(client);
+
+                // Is this request actually going to the homeserver?
+                const isRequestToHomeServer = url.origin === new URL(auth.homeserver).origin;
+                if (!isRequestToHomeServer) {
+                    throw new Error("Request appears to be for media endpoint but wrong homeserver!");
+                }
 
                 // Update or populate the server support map using a (usually) authenticated `/versions` call.
-                await tryUpdateServerSupportMap(csApi, accessToken);
+                await tryUpdateServerSupportMap(csApi, auth.accessToken);
 
                 // If we have server support (and a means of authentication), rewrite the URL to use MSC3916 endpoints.
-                if (serverSupportMap[csApi].supportsAuthedMedia && accessToken) {
-                    url = url.replace(/\/media\/v3\/(.*)\//, "/client/v1/media/$1/");
+                if (serverSupportMap[csApi].supportsAuthedMedia && auth.accessToken) {
+                    url.href = url.href.replace(/\/media\/v3\/(.*)\//, "/client/v1/media/$1/");
                 } // else by default we make no changes
             } catch (err) {
+                // In case of some error, we stay safe by not adding the access-token to the request.
+                auth = undefined;
                 console.error("SW: Error in request rewrite.", err);
             }
 
             // Add authentication and send the request. We add authentication even if MSC3916 endpoints aren't
             // being used to ensure patches like this work:
             // https://github.com/matrix-org/synapse/commit/2390b66bf0ec3ff5ffb0c7333f3c9b239eeb92bb
-            return fetch(url, fetchConfigForToken(accessToken));
+            return fetch(url, fetchConfigForToken(auth?.accessToken));
         })(),
     );
 });
@@ -106,35 +117,36 @@ async function tryUpdateServerSupportMap(clientApiUrl: string, accessToken?: str
 
 // Ideally we'd use the `Client` interface for `client`, but since it's not available (see 'fetch' listener), we use
 // unknown for now and force-cast it to something close enough later.
-async function getAccessToken(client: unknown): Promise<string | undefined> {
+async function getAuthData(client: unknown): Promise<{ accessToken: string; homeserver: string }> {
     // Access tokens are encrypted at rest, so while we can grab the "access token", we'll need to do work to get the
     // real thing.
     const encryptedAccessToken = await idbLoad("account", "mx_access_token");
 
     // We need to extract a user ID and device ID from localstorage, which means calling WebPlatform for the
     // read operation. Service workers can't access localstorage.
-    const { userId, deviceId } = await askClientForUserIdParams(client);
+    const { userId, deviceId, homeserver } = await askClientForUserIdParams(client);
 
     // ... and this is why we need the user ID and device ID: they're index keys for the pickle key table.
     const pickleKeyData = await idbLoad("pickleKey", [userId, deviceId]);
     if (pickleKeyData && (!pickleKeyData.encrypted || !pickleKeyData.iv || !pickleKeyData.cryptoKey)) {
-        console.error("SW: Invalid pickle key loaded - ignoring");
-        return undefined;
+        throw new Error("SW: Invalid pickle key loaded - ignoring");
     }
 
     // Finally, try decrypting the thing and return that. This may fail, but that's okay.
     try {
         const pickleKey = await buildAndEncodePickleKey(pickleKeyData, userId, deviceId);
-        return tryDecryptToken(pickleKey, encryptedAccessToken, ACCESS_TOKEN_IV);
+        const accessToken = await tryDecryptToken(pickleKey, encryptedAccessToken, ACCESS_TOKEN_IV);
+        return { accessToken, homeserver };
     } catch (e) {
-        console.error("SW: Error decrypting access token.", e);
-        return undefined;
+        throw new Error("SW: Error decrypting access token.", { cause: e });
     }
 }
 
 // Ideally we'd use the `Client` interface for `client`, but since it's not available (see 'fetch' listener), we use
 // unknown for now and force-cast it to something close enough inside the function.
-async function askClientForUserIdParams(client: unknown): Promise<{ userId: string; deviceId: string }> {
+async function askClientForUserIdParams(
+    client: unknown,
+): Promise<{ userId: string; deviceId: string; homeserver: string }> {
     return new Promise((resolve, reject) => {
         // Dev note: this uses postMessage, which is a highly insecure channel. postMessage is typically visible to other
         // tabs, windows, browser extensions, etc, making it far from ideal for sharing sensitive information. This is

src/vector/platform/WebPlatform.ts

@@ -14,6 +14,7 @@ import { Action } from "matrix-react-sdk/src/dispatcher/actions";
 import { CheckUpdatesPayload } from "matrix-react-sdk/src/dispatcher/payloads/CheckUpdatesPayload";
 import UAParser from "ua-parser-js";
 import { logger } from "matrix-js-sdk/src/logger";
+import { MatrixClientPeg } from "matrix-react-sdk/src/MatrixClientPeg";
 
 import VectorBasePlatform from "./VectorBasePlatform";
 import { parseQs } from "../url_utils";
@@ -62,10 +63,12 @@ export default class WebPlatform extends VectorBasePlatform {
             if (event.data?.["type"] === "userinfo" && event.data?.["responseKey"]) {
                 const userId = localStorage.getItem("mx_user_id");
                 const deviceId = localStorage.getItem("mx_device_id");
+                const homeserver = MatrixClientPeg.get()?.getHomeserverUrl();
                 event.source!.postMessage({
                     responseKey: event.data["responseKey"],
                     userId,
                     deviceId,
+                    homeserver,
                 });
             }
         } catch (e) {