fix(ipc): confine recorded video writes

electron/ipc/recording/storagePath.test.ts

@@ -0,0 +1,53 @@
+import path from "node:path";
+import { describe, expect, it } from "vitest";
+import { resolveRecordedVideoStoragePath } from "./storagePath";
+
+describe("resolveRecordedVideoStoragePath", () => {
+	const recordingsDir = path.resolve("recordings-root");
+
+	it.each([
+		"recording-0.webm",
+		"recording-1720588800000.mp4",
+		"recording-1720588800000-webcam.webm",
+		"recording-1720588800000-webcam.mp4",
+	])("accepts an app-generated recording name: %s", (fileName) => {
+		expect(resolveRecordedVideoStoragePath(recordingsDir, fileName)).toBe(
+			path.resolve(recordingsDir, fileName),
+		);
+	});
+
+	it.each([
+		"",
+		"../recording-1.webm",
+		"..\\recording-1.webm",
+		"nested/recording-1.webm",
+		"nested\\recording-1.webm",
+		"/tmp/recording-1.webm",
+		"C:\\temp\\recording-1.webm",
+		"\\\\server\\share\\recording-1.webm",
+		"recording-1.webm:payload",
+		"recording-1.webm\n",
+		"recording-1.webm\0",
+		"recording--1.webm",
+		"recording-1.5.webm",
+		"recording-1.mov",
+		"other-1.webm",
+		"recording-1-WEBCAM.webm",
+	])("rejects an untrusted recording name: %s", (fileName) => {
+		expect(() => resolveRecordedVideoStoragePath(recordingsDir, fileName)).toThrow(
+			"Invalid recording file name",
+		);
+	});
+
+	it.each([
+		{ label: "undefined", value: undefined },
+		{ label: "null", value: null },
+		{ label: "number", value: 1 },
+		{ label: "object", value: {} },
+		{ label: "array", value: [] },
+	])("rejects a non-string recording name: $label", ({ value }) => {
+		expect(() => resolveRecordedVideoStoragePath(recordingsDir, value)).toThrow(
+			"Invalid recording file name",
+		);
+	});
+});

electron/ipc/recording/storagePath.ts

@@ -0,0 +1,24 @@
+import path from "node:path";
+
+const RECORDED_VIDEO_FILE_NAME = /^recording-[0-9]+(?:-webcam)?\.(?:webm|mp4)$/;
+
+export function resolveRecordedVideoStoragePath(recordingsDir: string, fileName: unknown): string {
+	if (typeof fileName !== "string" || RECORDED_VIDEO_FILE_NAME.exec(fileName)?.[0] !== fileName) {
+		throw new Error("Invalid recording file name");
+	}
+
+	const resolvedRecordingsDir = path.resolve(recordingsDir);
+	const candidatePath = path.resolve(resolvedRecordingsDir, fileName);
+	const relativePath = path.relative(resolvedRecordingsDir, candidatePath);
+
+	if (
+		relativePath.length === 0 ||
+		relativePath === ".." ||
+		relativePath.startsWith(`..${path.sep}`) ||
+		path.isAbsolute(relativePath)
+	) {
+		throw new Error("Invalid recording file name");
+	}
+
+	return candidatePath;
+}

electron/ipc/register/recording.ts

@@ -68,6 +68,7 @@ import {
 	waitForNativeCaptureStart,
 	waitForNativeCaptureStop,
 } from "../recording/mac";
+import { resolveRecordedVideoStoragePath } from "../recording/storagePath";
 import {
 	attachWindowsCaptureLifecycle,
 	isNativeWindowsCaptureAvailable,
@@ -1747,10 +1748,10 @@ export function registerRecordingHandlers(
 		},
 	);
 
-	ipcMain.handle("store-recorded-video", async (_, videoData: ArrayBuffer, fileName: string) => {
+	ipcMain.handle("store-recorded-video", async (_, videoData: ArrayBuffer, fileName: unknown) => {
 		try {
 			const recordingsDir = await getRecordingsDir();
-			const videoPath = path.join(recordingsDir, fileName);
+			const videoPath = resolveRecordedVideoStoragePath(recordingsDir, fileName);
 			await fs.writeFile(videoPath, Buffer.from(videoData));
 			return await finalizeStoredVideo(videoPath);
 		} catch (error) {