CVE-2026-53522

## 1. Description The Nezha dashboard exposes two endpoints that create long-lived WebSocket streams to monitored agents: - `POST /api/v1/terminal` → `createTerminal()` (terminal.go:27-67) - `POST /api/v1/file` → `createFM()` (fm.go:28-67) Both call `rpc.NezhaHandlerSingleton.CreateStream(streamId, ...)` which inserts a new `ioStreamContext` into an **unbounded** `map[string]*ioStreamContext` (`s.ioStreams` in `io_stream.go:59-67`). There is **no per-user rate limit, no global semaphore, and no per-server connection cap**. Each stream allocates: 1. A `ioStreamContext` struct with several channels and sync primitives 2. Two goroutines via `StartStream()` (io_stream.go:358-369) — bidirectional `io.CopyBuffer` 3. A gRPC IOStream between the dashboard and the agent 4. An agent-side PTY/shell process **Vulnerable code:** `terminal.go:27-67` — `createTerminal`: ```go func createTerminal(c *gin.Context) (*model.CreateTerminalResponse, error) { // ... validation ... rpc.NezhaHandlerSingleton.CreateStream(streamId, getUid(c), server.ID) // ... sends TaskTypeTerminalGRPC to agent ... return &model.CreateTerminalResponse{...}, nil } ``` `fm.go:28-67` — `createFM`: ```go func createFM(c *gin.Context) (*model.CreateFMResponse, error) { // ... validation ... rpc.NezhaHandlerSingleton.CreateStream(streamId, getUid(c), server.ID) // ... sends TaskTypeFM to agent ... return &model.CreateFMResponse{...}, nil } ``` `io_stream.go:55-67` — `CreateStreamWithPurpose` (inserts into unbounded map): ```go func (s *NezhaHandler) CreateStreamWithPurpose(...) { s.ioStreamMutex.Lock() defer s.ioStreamMutex.Unlock() s.ioStreams[streamId] = &ioStreamContext{ creatorUserID: creatorUserID, targetServerID: targetServerID, purpose: purpose, userIoConnectCh: make(chan struct{}), agentIoConnectCh: make(chan struct{}), revokedCh: make(chan struct{}), } } ``` `io_stream.go:319-372` — `S