From 1c50a2c047ebdde5f805264d0fa2379cfbbe9666 Mon Sep 17 00:00:00 2001
From: automated-signal <37887102+automated-signal@users.noreply.github.com>
Date: Mon, 13 Apr 2026 11:53:49 -0500
Subject: [PATCH] Improve file handler check to add path separator

Co-authored-by: ayumi-signal <143036029+ayumi-signal@users.noreply.github.com>
---
 app/protocol_filter.node.ts                   |  17 +-
 ts/test-node/app/protocol_filter_test.node.ts | 161 +++++++++++++++++-
 2 files changed, 173 insertions(+), 5 deletions(-)

diff --git a/app/protocol_filter.node.ts b/app/protocol_filter.node.ts
index 3d436e6d26..17c68f0a4b 100644
--- a/app/protocol_filter.node.ts
+++ b/app/protocol_filter.node.ts
@@ -16,11 +16,17 @@ import {
   getUpdateCachePath,
 } from './attachments.node.ts';
 import { createLogger } from '../ts/logging/log.std.ts';
+import { isPathInside } from '../ts/util/isPathInside.node.ts';
 
 const log = createLogger('protocol_filter');
 
 type CallbackType = (response: string | ProtocolResponse) => void;
 
+export type FileHandlerType = (
+  request: ProtocolRequest,
+  callback: CallbackType
+) => void;
+
 function _eliminateAllAfterCharacter(
   string: string,
   character: string
@@ -50,7 +56,7 @@ export function _urlToPath(
   return withoutQuerystring;
 }
 
-function _createFileHandler({
+export function _createFileHandler({
   userDataPath,
   installPath,
   isWindows,
@@ -58,7 +64,7 @@ function _createFileHandler({
   userDataPath: string;
   installPath: string;
   isWindows: boolean;
-}) {
+}): FileHandlerType {
   const allowedRoots = [
     userDataPath,
     installPath,
@@ -71,6 +77,9 @@ function _createFileHandler({
     getTempPath(userDataPath),
     getUpdateCachePath(userDataPath),
   ];
+  const allowedRootsCased = allowedRoots.map(root =>
+    isWindows ? root.toLowerCase() : root
+  );
   return (request: ProtocolRequest, callback: CallbackType): void => {
     let targetPath;
 
@@ -102,8 +111,8 @@ function _createFileHandler({
         return;
       }
 
-      for (const root of allowedRoots) {
-        if (properCasing.startsWith(isWindows ? root.toLowerCase() : root)) {
+      for (const root of allowedRootsCased) {
+        if (isPathInside(properCasing, root)) {
           callback({ path: realPath });
           return;
         }
diff --git a/ts/test-node/app/protocol_filter_test.node.ts b/ts/test-node/app/protocol_filter_test.node.ts
index 5fca862f53..8830e8166a 100644
--- a/ts/test-node/app/protocol_filter_test.node.ts
+++ b/ts/test-node/app/protocol_filter_test.node.ts
@@ -2,10 +2,24 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import { assert } from 'chai';
+import type { ProtocolResponse } from 'electron';
+import * as sinon from 'sinon';
 
-import { _urlToPath } from '../../../app/protocol_filter.node.ts';
+import {
+  _createFileHandler,
+  _urlToPath,
+  type FileHandlerType,
+} from '../../../app/protocol_filter.node.ts';
 
 describe('Protocol Filter', () => {
+  beforeEach(function (this: Mocha.Context) {
+    this.sandbox = sinon.createSandbox();
+  });
+
+  afterEach(function (this: Mocha.Context) {
+    this.sandbox.restore();
+  });
+
   describe('_urlToPath', () => {
     it('returns proper file path for unix style file URI with querystring', () => {
       const path =
@@ -79,4 +93,149 @@ describe('Protocol Filter', () => {
       assert.strictEqual(actual, expected);
     });
   });
+
+  describe('_createFileHandler', () => {
+    function testFn({
+      fileHandler,
+      url,
+      expectedResult,
+    }: {
+      fileHandler: FileHandlerType;
+      url: string;
+      expectedResult: string | Partial<ProtocolResponse>;
+    }) {
+      const testCallback = sinon.stub();
+
+      const request = {
+        headers: {},
+        method: 'GET',
+        referrer: '',
+        url,
+      };
+      fileHandler(request, testCallback);
+      sinon.assert.calledWithMatch(testCallback, expectedResult);
+    }
+
+    describe('windows', () => {
+      before(function (this: Mocha.Context) {
+        if (process.platform !== 'win32') {
+          this.skip();
+        }
+      });
+
+      function getFileHandler(): FileHandlerType {
+        return _createFileHandler({
+          userDataPath: 'C:\\Users\\signaluser\\AppData\\Roaming\\Signal',
+          installPath:
+            'C:\\Users\\signaluser\\AppData\\Local\\Programs\\signal-desktop',
+          isWindows: true,
+        });
+      }
+
+      it('allows files in userData', () => {
+        testFn({
+          fileHandler: getFileHandler(),
+          url: 'file:///C:/Users/signaluser/AppData/Roaming/Signal/foo',
+          expectedResult: {
+            path: 'C:\\Users\\signaluser\\AppData\\Roaming\\Signal\\foo',
+          },
+        });
+      });
+
+      it('disallows files in other places', () => {
+        const fileHandler = getFileHandler();
+
+        testFn({
+          fileHandler,
+          url: 'file:///C:/Windows/foo',
+          expectedResult: { error: -10 },
+        });
+        testFn({
+          fileHandler,
+          url: 'file:///C:/Users/signaluser/AppData/Roaming/Signal Beta/foo',
+          expectedResult: { error: -10 },
+        });
+      });
+    });
+
+    describe('macos', () => {
+      before(function (this: Mocha.Context) {
+        if (process.platform === 'win32') {
+          this.skip();
+        }
+      });
+
+      function getFileHandler(): FileHandlerType {
+        return _createFileHandler({
+          userDataPath: '/Users/signaluser/Library/Application Support/Signal',
+          installPath: '/Applications/Signal',
+          isWindows: false,
+        });
+      }
+
+      it('allows files in userData', () => {
+        testFn({
+          fileHandler: getFileHandler(),
+          url: 'file:///Users/signaluser/Library/Application Support/Signal/foo',
+          expectedResult: {
+            path: '/Users/signaluser/Library/Application Support/Signal/foo',
+          },
+        });
+      });
+
+      it('disallows files in other places', () => {
+        const fileHandler = getFileHandler();
+
+        testFn({
+          fileHandler,
+          url: 'file:///Applications/foo',
+          expectedResult: { error: -10 },
+        });
+        testFn({
+          fileHandler,
+          url: 'file:///Users/signaluser/Library/Application Support/Signal Beta/foo',
+          expectedResult: { error: -10 },
+        });
+      });
+    });
+
+    describe('linux', () => {
+      before(function (this: Mocha.Context) {
+        if (process.platform === 'win32') {
+          this.skip();
+        }
+      });
+
+      function getFileHandler(): FileHandlerType {
+        return _createFileHandler({
+          userDataPath: '/home/signaluser/.config/Signal',
+          installPath: '/usr/bin/signal-desktop',
+          isWindows: false,
+        });
+      }
+
+      it('allows files in userData', () => {
+        testFn({
+          fileHandler: getFileHandler(),
+          url: 'file:///home/signaluser/.config/Signal/foo',
+          expectedResult: { path: '/home/signaluser/.config/Signal/foo' },
+        });
+      });
+
+      it('disallows files in other places', () => {
+        const fileHandler = getFileHandler();
+
+        testFn({
+          fileHandler,
+          url: 'file:///usr/bin/foo',
+          expectedResult: { error: -10 },
+        });
+        testFn({
+          fileHandler,
+          url: 'file:///home/signaluser/.config/Signal Beta/foo',
+          expectedResult: { error: -10 },
+        });
+      });
+    });
+  });
 });