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

pull/28194/head
David Baker 2024-10-15 12:37:21 +01:00
parent 8904453bbf
commit 8d7f2b5c13
2 changed files with 33 additions and 18 deletions
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48
src/serviceworker/index.ts
View File

@ -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

3
src/vector/platform/WebPlatform.ts
View File

@ -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) {