diff --git a/packages/cloud/src/CloudAPI.ts b/packages/cloud/src/CloudAPI.ts
index d1c3f89c2b..57f57762a9 100644
--- a/packages/cloud/src/CloudAPI.ts
+++ b/packages/cloud/src/CloudAPI.ts
@@ -111,6 +111,8 @@ export class CloudAPI {
 	async shareTask(taskId: string, visibility: ShareVisibility = "organization"): Promise<ShareResponse> {
 		this.log(`[CloudAPI] Sharing task ${taskId} with visibility: ${visibility}`)
 
+		// The server should validate that the authenticated user owns this task
+		// by checking the session token's user ID against the task's owner
 		const response = await this.request("/api/extension/share", {
 			method: "POST",
 			body: JSON.stringify({ taskId, visibility }),
diff --git a/packages/cloud/src/bridge/BridgeOrchestrator.ts b/packages/cloud/src/bridge/BridgeOrchestrator.ts
index 15b5c65eb2..1d98ee73a1 100644
--- a/packages/cloud/src/bridge/BridgeOrchestrator.ts
+++ b/packages/cloud/src/bridge/BridgeOrchestrator.ts
@@ -191,6 +191,7 @@ export class BridgeOrchestrator {
 			instanceId: this.instanceId,
 			appProperties: this.appProperties,
 			gitProperties: this.gitProperties,
+			userId: this.userId,
 		})
 	}
 
diff --git a/packages/cloud/src/bridge/TaskChannel.ts b/packages/cloud/src/bridge/TaskChannel.ts
index 433e740d4e..c20dadd2ac 100644
--- a/packages/cloud/src/bridge/TaskChannel.ts
+++ b/packages/cloud/src/bridge/TaskChannel.ts
@@ -26,8 +26,9 @@ type TaskEventMapping = {
 	createPayload: (task: TaskLike, ...args: any[]) => any // eslint-disable-line @typescript-eslint/no-explicit-any
 }
 
-// eslint-disable-next-line @typescript-eslint/no-empty-object-type
-interface TaskChannelOptions extends BaseChannelOptions {}
+interface TaskChannelOptions extends BaseChannelOptions {
+	userId?: string
+}
 
 /**
  * Manages task-level communication channels.
@@ -41,6 +42,7 @@ export class TaskChannel extends BaseChannel<
 	private subscribedTasks: Map<string, TaskLike> = new Map()
 	private pendingTasks: Map<string, TaskLike> = new Map()
 	private taskListeners: Map<string, Map<TaskBridgeEventName, TaskEventListener>> = new Map()
+	private readonly userId?: string
 
 	private readonly eventMapping: readonly TaskEventMapping[] = [
 		{
@@ -74,6 +76,7 @@ export class TaskChannel extends BaseChannel<
 
 	constructor(options: TaskChannelOptions) {
 		super(options)
+		this.userId = options.userId
 	}
 
 	protected async handleCommandImplementation(command: TaskBridgeCommand): Promise<void> {
@@ -160,7 +163,10 @@ export class TaskChannel extends BaseChannel<
 	public async subscribeToTask(task: TaskLike, _socket: Socket): Promise<void> {
 		const taskId = task.taskId
 
-		await this.publish(TaskSocketEvents.JOIN, { taskId }, (response: JoinResponse) => {
+		// Include userId in the join request for server-side validation
+		const joinPayload = this.userId ? { taskId, userId: this.userId } : { taskId }
+
+		await this.publish(TaskSocketEvents.JOIN, joinPayload, (response: JoinResponse) => {
 			if (response.success) {
 				console.log(`[TaskChannel#subscribeToTask] subscribed to ${taskId}`)
 				this.subscribedTasks.set(taskId, task)
diff --git a/packages/cloud/src/bridge/__tests__/TaskChannel.test.ts b/packages/cloud/src/bridge/__tests__/TaskChannel.test.ts
index 1f13da9661..c35a1a3d45 100644
--- a/packages/cloud/src/bridge/__tests__/TaskChannel.test.ts
+++ b/packages/cloud/src/bridge/__tests__/TaskChannel.test.ts
@@ -403,4 +403,130 @@ describe("TaskChannel", () => {
 			errorSpy.mockRestore()
 		})
 	})
+
+	describe("User ID Validation", () => {
+		it("should include userId in JOIN payload when userId is provided", async () => {
+			const userId = "test-user-123"
+			const channelWithUserId = new TaskChannel({
+				instanceId,
+				appProperties,
+				userId,
+			})
+
+			// Mock the publish method to capture the payload
+			let capturedPayload: any = null
+			const channel = channelWithUserId as any
+			channel.publish = vi.fn((event: string, data: any, callback?: Function) => {
+				if (event === TaskSocketEvents.JOIN) {
+					capturedPayload = data
+					if (callback) {
+						callback({ success: true })
+					}
+				}
+				return true
+			})
+
+			await channelWithUserId.onConnect(mockSocket)
+			await channel.subscribeToTask(mockTask, mockSocket)
+
+			// Verify the JOIN payload includes userId
+			expect(capturedPayload).toEqual({
+				taskId,
+				userId,
+			})
+		})
+
+		it("should not include userId in JOIN payload when userId is not provided", async () => {
+			// Mock the publish method to capture the payload
+			let capturedPayload: any = null
+			const channel = taskChannel as any
+			channel.publish = vi.fn((event: string, data: any, callback?: Function) => {
+				if (event === TaskSocketEvents.JOIN) {
+					capturedPayload = data
+					if (callback) {
+						callback({ success: true })
+					}
+				}
+				return true
+			})
+
+			await taskChannel.onConnect(mockSocket)
+			await channel.subscribeToTask(mockTask, mockSocket)
+
+			// Verify the JOIN payload does not include userId
+			expect(capturedPayload).toEqual({
+				taskId,
+			})
+		})
+
+		it("should handle subscription failure when user is not authorized", async () => {
+			const userId = "unauthorized-user"
+			const channelWithUserId = new TaskChannel({
+				instanceId,
+				appProperties,
+				userId,
+			})
+
+			// Mock the publish method to simulate authorization failure
+			const channel = channelWithUserId as any
+			channel.publish = vi.fn((event: string, data: any, callback?: Function) => {
+				if (event === TaskSocketEvents.JOIN && callback) {
+					// Simulate authorization failure
+					callback({
+						success: false,
+						error: "User not authorized to access this task",
+					})
+				}
+				return true
+			})
+
+			const errorSpy = vi.spyOn(console, "error")
+
+			await channelWithUserId.onConnect(mockSocket)
+			await channel.subscribeToTask(mockTask, mockSocket)
+
+			// Verify error was logged
+			expect(errorSpy).toHaveBeenCalledWith(
+				`[TaskChannel#subscribeToTask] failed to subscribe to ${taskId}: User not authorized to access this task`,
+			)
+
+			// Verify task was not added to subscribedTasks
+			expect(channel.subscribedTasks.has(taskId)).toBe(false)
+
+			errorSpy.mockRestore()
+		})
+
+		it("should successfully subscribe when user is authorized", async () => {
+			const userId = "authorized-user"
+			const channelWithUserId = new TaskChannel({
+				instanceId,
+				appProperties,
+				userId,
+			})
+
+			// Mock the publish method to simulate successful authorization
+			const channel = channelWithUserId as any
+			channel.publish = vi.fn((event: string, data: any, callback?: Function) => {
+				if (event === TaskSocketEvents.JOIN && callback) {
+					// Simulate successful authorization
+					callback({ success: true })
+				}
+				return true
+			})
+
+			const logSpy = vi.spyOn(console, "log")
+
+			await channelWithUserId.onConnect(mockSocket)
+			await channel.subscribeToTask(mockTask, mockSocket)
+
+			// Verify success was logged
+			expect(logSpy).toHaveBeenCalledWith(`[TaskChannel#subscribeToTask] subscribed to ${taskId}`)
+
+			// Verify task was added to subscribedTasks
+			expect(channel.subscribedTasks.has(taskId)).toBe(true)
+			expect(channel.subscribedTasks.get(taskId)).toBe(mockTask)
+
+			logSpy.mockRestore()
+		})
+	})
 })