fix(security): CORS allowlist, URL scheme guard, state perms, ZIP slip, mirror docs

Phase 3 security audit follow-up. Medium and low-severity hardenings
plus a deferred-work plan for the cross-repo stream-token rollout.

Stream server CORS: replace the wildcard Access-Control-Allow-Origin
with an allowlist that echoes back only torrentclaw.com,
app.torrentclaw.com, the local Next dev port (3030 — matches the web
repo package.json) and any extras the operator adds via the new
downloads.cors_extra_origins TOML key. A Vary: Origin header is now
emitted whenever the request carries an Origin header so an
intermediate cache cannot serve a stale ACAO to a different origin.

URL scheme guard: openBrowser and OpenPlayer refuse any URL that is
not http(s). Combined with passing the URL after "--" wherever the
launched helper supports it (open, mpv, vlc, cvlc), this stops a
leading "-" from being parsed as a switch by the spawned process.

State file permissions: WriteState now writes 0o600 so the agent ID,
PID and counters cannot be enumerated by another local user on a
shared host. Matches the existing config file mode.

ZIP slip defense-in-depth: extractZip extracts the safety check into
safeZipPath, which canonicalises the entry name (normalising
backslashes to "/"), rejects "..", "../" prefix and "/../" interior
components, and verifies the final destination stays inside destDir
before opening any file.

Mirror fallback: documented the design for multi-provider
mirrors.json hosting in the comment block on DefaultStaticFallbackURLs
and added a follow-up note about signing it with the same ed25519
release key. The list is kept at one provider until the second host
is provisioned and added to torrentclaw-web's STATIC_FALLBACKS.

Deferred work: a new plan document Docs/plans/security-stream-token.md
covers the per-task stream token (Phase 2.2 of the original audit)
which requires coordinated web + CLI work and ships separately.

Docs/plans/security-stream-token.md

@@ -0,0 +1,131 @@
+# Phase 2.2 — Per-task stream token (deferred)
+
+Status: deferred. Requires coordinated change in the web app
+(`torrentclaw-web`) and the CLI daemon. Pulled out of the Phase 2
+security pass because the CLI-only fixes (UPnP opt-in, SSE caps,
+signed self-update) ship without web-side work; the stream-token
+work cannot.
+
+## Problem
+
+`/stream`, `/playlist.m3u` and `/hls/<sessionID>/...` on the daemon
+HTTP server have no authentication. Today, anyone who can reach the
+listener and guesses (or learns) the `taskID` (for `/stream`) or
+`sessionID` (for `/hls`) can fetch the active file.
+
+Mitigations already in place after Phase 1+2:
+
+- `sessionID` is restricted to a safe regex and is a server-issued
+  UUID v4 (122-bit entropy, not enumerable in practice).
+- `/health` no longer leaks the active filename, taskID prefix or
+  client IP to remote callers (loopback diagnostics preserved).
+- UPnP is opt-in, so by default the daemon is not exposed to the
+  public internet.
+- The web client probes `/health` to pick LAN vs Tailscale.
+
+Residual risk:
+
+- On a shared LAN (open Wi-Fi, office network, dorm) any device can
+  reach the listener and brute-force `?id=<taskID>` against
+  `/stream`. taskIDs are also UUIDs, so this is high entropy, but
+  the URL may leak through browser history, sharing, screen capture
+  or a passive logger and there is no second factor.
+- A user who explicitly opts into UPnP exposes the same surface to
+  the entire internet.
+
+A per-task secret carried in the URL closes this without breaking
+the `<video src>` flow (the browser cannot attach `Authorization`
+headers to media elements, but it can append a query parameter).
+
+## Design
+
+Both ends agree on a per-task secret token. The web generates it
+when the user requests streaming; the daemon receives the
+`(taskID, token)` pair and validates the token on every `/stream`
+and `/hls/...` request.
+
+### Web side (`torrentclaw-web`)
+
+When the user clicks "Stream":
+
+1. Generate `streamToken = crypto.randomBytes(32).toString("hex")`
+   server-side (NOT browser, so it never lives in client storage
+   longer than the page lifetime).
+2. Persist `(taskID, streamToken, expiresAt)` in `download_task`
+   (new columns or a sibling table). Token expires e.g. 6 h after
+   issue or on explicit revoke.
+3. Push the token to the daemon over the existing heartbeat / sync
+   channel that already carries `streamRequested`. Add a
+   `streamToken` field next to it. The daemon trusts that channel
+   (it is authenticated agent ↔ origin).
+4. Include the token in the stream URLs the API returns to the
+   browser:
+   `http://<host>:<port>/stream?id=<taskID>&t=<streamToken>` and
+   the `/hls/<sessionID>` URLs gain `?t=<streamToken>` too.
+
+Files that will need to change:
+
+- `src/lib/services/agent.ts` — extend the stream-request payload
+  with `streamToken`.
+- `src/lib/db/schema.ts` — column / table for the token.
+- `src/lib/services/stream-resolve.ts` — append `&t=` to the URLs
+  it builds.
+- `src/lib/stream-probe.ts` — keep probing `/health` (no token),
+  then append `&t=` to the winning stream URL before returning.
+- `src/middleware.ts` — no CORS change required (browser still hits
+  daemon directly).
+
+### CLI side
+
+- `internal/agent/types.go` / `internal/agent/sync.go` — accept and
+  store `streamToken` next to `streamRequested`.
+- `internal/agent/daemon.go` — when the heartbeat reports a new
+  active stream task, push the token into the stream server via a
+  setter: `streamSrv.SetTaskToken(taskID, token)`.
+- `internal/engine/stream_server.go`:
+    - New field `tokens map[string]string` guarded by mutex.
+    - `SetTaskToken(taskID, token)` and `ClearTaskToken(taskID)`.
+    - `handler` (`/stream`) extracts `?id=` and `?t=`, checks the
+      token with `subtle.ConstantTimeCompare`; 404 on mismatch.
+    - `hlsHandler` (`/hls/<sessionID>/...`) needs an HLS-session
+      → token mapping, since the path carries `sessionID` not
+      `taskID`. Store the token on the `HLSSession` at start and
+      validate per request.
+
+### Backwards compatibility
+
+- The daemon must accept token-less requests for one minor version
+  so a newer daemon can still serve an older web (and vice-versa).
+  Gate the check on a config flag (`require_stream_token`,
+  default false in the first release, default true in the next).
+- The `<video src>` form supports query parameters, so the only
+  user-visible change is the URL string.
+
+## Open questions to resolve before implementing
+
+1. Token TTL. 6 h gives plenty of room for a movie + pause +
+   resume; longer means the post-leak window is wider.
+2. Where to store the token in `download_task` — same row, or a
+   sibling `download_stream_token` table that we can rotate
+   without writing to the task row.
+3. Should `/playlist.m3u` (VLC) embed the token directly, or use
+   a one-shot redeem URL? VLC URL ends up in history.
+4. Token reuse across HLS reconnects — yes, scoped to the
+   `HLSSession`, invalidated on `Close()`.
+5. Do we want a daemon flag `--require-stream-token` independent
+   of config, for users to flip on quickly without editing TOML?
+
+## Effort estimate
+
+- CLI: ~3 h
+- Web: ~3 h
+- Migration + rollout (config flag flip): 1 release cycle of soak.
+
+## Why not now
+
+- Cross-repo coordination raises commit blast radius beyond what
+  the Phase 2 security pass should carry.
+- Web work needs DB migration + UI surfaces (the "stream link
+  expired" path).
+- Phase 2 hardenings ship value today without it; this is the
+  defense-in-depth layer on top.

internal/agent/mirror_client.go

@@ -37,7 +37,17 @@ type MirrorsResponse struct {
 // Hard-coded here (not loaded from config) because the whole point is to
 // have something to consult when config-driven URLs all fail.
 //
-// Keep in sync with src/lib/mirrors-config.ts → STATIC_FALLBACKS on the web.
+// Today there is one provider (GitHub Pages). The slice is intentionally
+// shaped to take more — a second independent host (Cloudflare Pages,
+// IPFS-Fleek, etc.) should be added as soon as it is provisioned. Keep
+// any addition in sync with `STATIC_FALLBACKS` in
+// `torrentclaw-web/src/lib/mirrors-config.ts` and `Docs/plans/security-stream-token.md`.
+//
+// Future hardening: sign mirrors.json with the same ed25519 release key
+// (or a sibling) so a hijack of any single static host cannot serve a
+// malicious mirror list. Today the only signal is "agreement between
+// independent providers" via cross-checking, which we leave to the
+// operator.
 var DefaultStaticFallbackURLs = []string{
 	"https://torrentclaw.github.io/mirrors/mirrors.json",
 }

internal/agent/state.go

@@ -45,9 +45,13 @@ func WriteState(state *DaemonState) {
 		return
 	}
 
-	// Write to temp file then rename for atomicity
+	// Write to temp file then rename for atomicity. 0o600 keeps the file
+	// readable only by the owning user — the state contains agentID, PID
+	// and counters which are useful to a co-tenant on a shared host for
+	// fingerprinting the daemon, and we already use 0o600 for the config
+	// file. No need for cross-user readability here.
 	tmp := path + ".tmp"
-	if err := os.WriteFile(tmp, data, 0o644); err != nil {
+	if err := os.WriteFile(tmp, data, 0o600); err != nil {
 		return
 	}
 	os.Rename(tmp, path)

internal/cmd/daemon.go

@@ -241,6 +241,7 @@ func runDaemonStart() error {
 	// Create persistent stream server
 	streamSrv := engine.NewStreamServer(cfg.Download.StreamPort)
 	streamSrv.SetUPnPEnabled(cfg.Download.EnableUPnP)
+	streamSrv.SetCORSAllowedOrigins(cfg.Download.CORSExtraOrigins)
 	// Reap HLS tmpdirs left over from a previous daemon run before we start
 	// accepting new sessions. The in-memory registry doesn't survive a
 	// restart, so without this disk usage grows unbounded across restarts.

internal/cmd/helpers.go

@@ -9,12 +9,21 @@ import (
 )
 
 // openBrowser opens a URL in the default browser.
+//
+// The URL is restricted to http(s) so that a hostile caller cannot trick
+// xdg-open/open into interpreting it as a flag (a leading "-" would otherwise
+// match a switch on every helper we shell out to). Where the helper supports
+// it we also append "--" to terminate switch parsing as belt-and-braces.
 func openBrowser(url string) {
+	if !isSafeBrowserURL(url) {
+		return
+	}
 	var c *exec.Cmd
 	switch runtime.GOOS {
 	case "darwin":
-		c = exec.Command("open", url)
+		c = exec.Command("open", "--", url)
 	case "windows":
+		// rundll32 does not parse switches from positional args.
 		c = exec.Command("rundll32", "url.dll,FileProtocolHandler", url)
 	default: // linux, freebsd
 		c = exec.Command("xdg-open", url)
@@ -22,6 +31,12 @@ func openBrowser(url string) {
 	_ = c.Start() // fire and forget; best-effort
 }
 
+// isSafeBrowserURL accepts only http(s) URLs. Other schemes (file://, javascript:,
+// data:, ...) and flag-shaped strings ("--help") are rejected.
+func isSafeBrowserURL(url string) bool {
+	return strings.HasPrefix(url, "http://") || strings.HasPrefix(url, "https://")
+}
+
 // defaultDownloadDir returns a sensible default download directory.
 func defaultDownloadDir() string {
 	home, _ := os.UserHomeDir()

internal/cmd/helpers_test.go

@@ -31,6 +31,32 @@ func TestExpandHome(t *testing.T) {
 	}
 }
 
+func TestIsSafeBrowserURL(t *testing.T) {
+	good := []string{
+		"http://localhost:3000",
+		"https://torrentclaw.com/some/path?q=1",
+	}
+	bad := []string{
+		"--help",
+		"-version",
+		"file:///etc/passwd",
+		"javascript:alert(1)",
+		"data:text/html,foo",
+		"ftp://example.com",
+		"",
+	}
+	for _, u := range good {
+		if !isSafeBrowserURL(u) {
+			t.Errorf("isSafeBrowserURL(%q) = false, want true", u)
+		}
+	}
+	for _, u := range bad {
+		if isSafeBrowserURL(u) {
+			t.Errorf("isSafeBrowserURL(%q) = true, want false", u)
+		}
+	}
+}
+
 func TestDefaultDownloadDir(t *testing.T) {
 	dir := defaultDownloadDir()
 	if dir == "" {

internal/config/config.go

@@ -50,6 +50,7 @@ type DownloadConfig struct {
 	ListenPort       int             `toml:"listen_port"`        // fixed port for incoming peer connections (default: 42069, 0 = random)
 	StreamPort       int             `toml:"stream_port"`        // fixed port for streaming HTTP server (default: 11818)
 	EnableUPnP       bool            `toml:"enable_upnp"`        // map StreamPort to the WAN via UPnP/NAT-PMP (default: false; opt-in because it exposes the unauthenticated /stream + /hls endpoints to the public internet)
+	CORSExtraOrigins []string        `toml:"cors_extra_origins"` // extra browser origins added on top of the baked-in allowlist (torrentclaw.com, app.torrentclaw.com, localhost:3030)
 	WebRTC           WebRTCConfig    `toml:"webrtc"`
 	Transcode        TranscodeConfig `toml:"transcode"`
 }

internal/engine/stream_player.go

@@ -4,14 +4,23 @@ import (
 	"fmt"
 	"os/exec"
 	"runtime"
+	"strings"
 )
 
 // OpenPlayer attempts to open a media player with the given stream URL.
 // Returns the player name and the running command.
 // If override is set, it uses that command directly.
+//
+// The URL is required to be http(s) so a hostile-looking value (e.g. starting
+// with `--`) is not interpreted as a switch by mpv/vlc/xdg-open/open. The
+// `--` separator is also appended before the URL where the helper supports
+// it.
 func OpenPlayer(url, override string) (string, *exec.Cmd, error) {
+	if !isSafePlayerURL(url) {
+		return "", nil, fmt.Errorf("refusing to open non-http(s) URL")
+	}
 	if override != "" {
-		cmd := exec.Command(override, url)
+		cmd := exec.Command(override, "--", url)
 		if err := cmd.Start(); err != nil {
 			return override, nil, fmt.Errorf("start %s: %w", override, err)
 		}
@@ -20,7 +29,7 @@ func OpenPlayer(url, override string) (string, *exec.Cmd, error) {
 
 	// Try mpv first (best streaming support)
 	if path, err := exec.LookPath("mpv"); err == nil {
-		cmd := exec.Command(path, "--no-terminal", url)
+		cmd := exec.Command(path, "--no-terminal", "--", url)
 		if err := cmd.Start(); err == nil {
 			return "mpv", cmd, nil
 		}
@@ -28,7 +37,7 @@ func OpenPlayer(url, override string) (string, *exec.Cmd, error) {
 
 	// Try VLC
 	if path, err := exec.LookPath("vlc"); err == nil {
-		cmd := exec.Command(path, url)
+		cmd := exec.Command(path, "--", url)
 		if err := cmd.Start(); err == nil {
 			return "vlc", cmd, nil
 		}
@@ -36,7 +45,7 @@ func OpenPlayer(url, override string) (string, *exec.Cmd, error) {
 
 	// Try cvlc (VLC headless)
 	if path, err := exec.LookPath("cvlc"); err == nil {
-		cmd := exec.Command(path, url)
+		cmd := exec.Command(path, "--", url)
 		if err := cmd.Start(); err == nil {
 			return "vlc (headless)", cmd, nil
 		}
@@ -51,6 +60,9 @@ func OpenPlayer(url, override string) (string, *exec.Cmd, error) {
 }
 
 func openBrowser(url string) (string, *exec.Cmd, error) {
+	if !isSafePlayerURL(url) {
+		return "", nil, fmt.Errorf("refusing to open non-http(s) URL")
+	}
 	switch runtime.GOOS {
 	case "linux":
 		if path, err := exec.LookPath("xdg-open"); err == nil {
@@ -60,7 +72,7 @@ func openBrowser(url string) (string, *exec.Cmd, error) {
 			}
 		}
 	case "darwin":
-		cmd := exec.Command("/usr/bin/open", url)
+		cmd := exec.Command("/usr/bin/open", "--", url)
 		if err := cmd.Start(); err == nil {
 			return "browser", cmd, nil
 		}
@@ -72,3 +84,9 @@ func openBrowser(url string) (string, *exec.Cmd, error) {
 	}
 	return "", nil, fmt.Errorf("no browser opener found")
 }
+
+// isSafePlayerURL guards the helpers above against URLs that could be
+// interpreted as command-line switches by the launched player.
+func isSafePlayerURL(url string) bool {
+	return strings.HasPrefix(url, "http://") || strings.HasPrefix(url, "https://")
+}

internal/engine/stream_server.go

@@ -56,6 +56,12 @@ type StreamServer struct {
 	// would let any scanner enumerate active downloads. LAN and Tailscale
 	// access keep working without UPnP.
 	enableUPnP bool
+	// corsExtraOrigins are operator-configured origins added to the default
+	// allowlist defined in validate.go. Set before Listen().
+	corsExtraOrigins []string
+	// corsAllowlist is computed at Listen() time and treated as read-only
+	// thereafter so per-request reads need no locking.
+	corsAllowlist map[string]struct{}
 
 	hls *HLSSessionRegistry // HLS sessions served on /hls/<id>/...
 
@@ -86,12 +92,57 @@ func (ss *StreamServer) SetUPnPEnabled(enabled bool) {
 	ss.enableUPnP = enabled
 }
 
+// SetCORSAllowedOrigins replaces the operator-supplied extra origins. The
+// default allowlist (torrentclaw.com / app.torrentclaw.com / localhost dev
+// ports) is always merged in. Call before Listen().
+func (ss *StreamServer) SetCORSAllowedOrigins(origins []string) {
+	ss.corsExtraOrigins = origins
+}
+
+// writeCORSHeaders writes the per-origin CORS response headers when the
+// request carries an Origin header that matches the allowlist. Returns true
+// if the handler must short-circuit (preflight OPTIONS). Media-tag requests
+// (no Origin header) bypass this entirely.
+//
+// `Vary: Origin` is emitted whenever an Origin header is present (matched
+// or not) so any intermediate cache keys the response per-origin and a
+// later request with a different origin cannot be served a stale ACAO.
+func (ss *StreamServer) writeCORSHeaders(w http.ResponseWriter, r *http.Request, expose string) (preflight bool) {
+	origin := r.Header.Get("Origin")
+	if origin == "" {
+		return false
+	}
+	w.Header().Add("Vary", "Origin")
+	if _, ok := ss.corsAllowlist[origin]; !ok {
+		// Unknown origin — do not emit CORS headers so the browser blocks
+		// the response. Still return without short-circuiting so a non-CORS
+		// caller (e.g. curl) keeps working.
+		return false
+	}
+	w.Header().Set("Access-Control-Allow-Origin", origin)
+	w.Header().Set("Access-Control-Allow-Methods", "GET, HEAD, OPTIONS")
+	w.Header().Set("Access-Control-Allow-Headers", "Range")
+	if expose != "" {
+		w.Header().Set("Access-Control-Expose-Headers", expose)
+	}
+	if r.Method == http.MethodOptions {
+		w.WriteHeader(http.StatusNoContent)
+		return true
+	}
+	return false
+}
+
 // HLS returns the HLS session registry for this server. Daemon code uses it
 // to register a session when the backend asks for HLS playback.
 func (ss *StreamServer) HLS() *HLSSessionRegistry { return ss.hls }
 
 // Listen starts the HTTP server on the configured port. Call once at daemon startup.
 func (ss *StreamServer) Listen(ctx context.Context) error {
+	// Freeze the CORS allowlist before the first request can land. After
+	// this point the map is treated as read-only so handlers can probe it
+	// without locking.
+	ss.corsAllowlist = buildCORSAllowlist(ss.corsExtraOrigins)
+
 	mux := http.NewServeMux()
 	mux.HandleFunc("/stream", ss.handler)
 	mux.HandleFunc("/health", ss.healthHandler)
@@ -306,16 +357,8 @@ func (ss *StreamServer) HLSURLsJSON(sessionID string) string {
 func (ss *StreamServer) hlsHandler(w http.ResponseWriter, r *http.Request) {
 	ss.lastActivity.Store(time.Now().UnixNano())
 
-	// CORS for app.torrentclaw.com → 127.0.0.1/Tailscale daemon.
-	if origin := r.Header.Get("Origin"); origin != "" {
-		w.Header().Set("Access-Control-Allow-Origin", "*")
-		w.Header().Set("Access-Control-Allow-Methods", "GET, HEAD, OPTIONS")
-		w.Header().Set("Access-Control-Allow-Headers", "Range")
-		w.Header().Set("Access-Control-Expose-Headers", "Content-Length, Content-Range, Accept-Ranges")
-		if r.Method == http.MethodOptions {
-			w.WriteHeader(http.StatusNoContent)
-			return
-		}
+	if ss.writeCORSHeaders(w, r, "Content-Length, Content-Range, Accept-Ranges") {
+		return
 	}
 
 	rest := strings.TrimPrefix(r.URL.Path, "/hls/")
@@ -414,6 +457,9 @@ func (ss *StreamServer) serveSubtitlePlaylist(w http.ResponseWriter, r *http.Req
 //
 //	curl http://<tailscale-ip>:<port>/health
 func (ss *StreamServer) healthHandler(w http.ResponseWriter, r *http.Request) {
+	if ss.writeCORSHeaders(w, r, "") {
+		return
+	}
 	ss.mu.RLock()
 	provider := ss.provider
 	taskID := ss.taskID
@@ -470,15 +516,8 @@ func (ss *StreamServer) healthHandler(w http.ResponseWriter, r *http.Request) {
 // VLC fetches this playlist and applies the EXTVLCOPT directives automatically,
 // enabling automatic audio/subtitle track selection on all VLC platforms (desktop + mobile).
 func (ss *StreamServer) playlistHandler(w http.ResponseWriter, r *http.Request) {
-	// CORS — handle preflight before doing any work (consistent with handler)
-	if origin := r.Header.Get("Origin"); origin != "" {
-		w.Header().Set("Access-Control-Allow-Origin", "*")
-		w.Header().Set("Access-Control-Allow-Methods", "GET, HEAD, OPTIONS")
-		w.Header().Set("Access-Control-Allow-Headers", "Range")
-		if r.Method == http.MethodOptions {
-			w.WriteHeader(http.StatusNoContent)
-			return
-		}
+	if ss.writeCORSHeaders(w, r, "") {
+		return
 	}
 
 	q := r.URL.Query()
@@ -548,17 +587,8 @@ func (ss *StreamServer) handler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// CORS headers — only when browser sends Origin (HTTPS site → localhost)
-	if origin := r.Header.Get("Origin"); origin != "" {
-		w.Header().Set("Access-Control-Allow-Origin", "*")
-		w.Header().Set("Access-Control-Allow-Methods", "GET, HEAD, OPTIONS")
-		w.Header().Set("Access-Control-Allow-Headers", "Range")
-		w.Header().Set("Access-Control-Expose-Headers", "Content-Length, Content-Range, Accept-Ranges")
-
-		if r.Method == http.MethodOptions {
-			w.WriteHeader(http.StatusNoContent)
-			return
-		}
+	if ss.writeCORSHeaders(w, r, "Content-Length, Content-Range, Accept-Ranges") {
+		return
 	}
 
 	rawReader := provider.NewFileReader(r.Context())

internal/engine/stream_server_test.go

@@ -429,6 +429,71 @@ func TestStreamServer_Health_NonLoopback_NoLeak(t *testing.T) {
 	}
 }
 
+// TestStreamServer_CORS_Allowlist verifica que sólo los origenes en la
+// allowlist reciben Access-Control-Allow-Origin y que ningún otro origen
+// es eco-reflejado.
+func TestStreamServer_CORS_Allowlist(t *testing.T) {
+	srv := NewStreamServer(0)
+	ctx := context.Background()
+	if err := srv.Listen(ctx); err != nil {
+		t.Fatalf("Listen: %v", err)
+	}
+	defer srv.Shutdown(ctx)
+
+	cases := []struct {
+		origin    string
+		wantAllow bool
+	}{
+		{"https://app.torrentclaw.com", true},
+		{"https://torrentclaw.com", true},
+		{"http://localhost:3030", true},
+		{"http://127.0.0.1:3030", true},
+		{"https://evil.example", false},
+		{"null", false},
+		{"", false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.origin, func(t *testing.T) {
+			rr := httptest.NewRecorder()
+			req := httptest.NewRequest(http.MethodOptions, "/health", nil)
+			if tc.origin != "" {
+				req.Header.Set("Origin", tc.origin)
+			}
+			srv.healthHandler(rr, req)
+			got := rr.Header().Get("Access-Control-Allow-Origin")
+			if tc.wantAllow {
+				if got != tc.origin {
+					t.Errorf("origin %q: ACAO = %q, want %q", tc.origin, got, tc.origin)
+				}
+			} else if got != "" {
+				t.Errorf("origin %q: ACAO leaked as %q, expected empty", tc.origin, got)
+			}
+		})
+	}
+}
+
+// TestStreamServer_CORS_ExtraOrigin verifica que SetCORSAllowedOrigins añade
+// origins al baseline sin removerlos.
+func TestStreamServer_CORS_ExtraOrigin(t *testing.T) {
+	srv := NewStreamServer(0)
+	srv.SetCORSAllowedOrigins([]string{"https://custom.example"})
+	ctx := context.Background()
+	if err := srv.Listen(ctx); err != nil {
+		t.Fatalf("Listen: %v", err)
+	}
+	defer srv.Shutdown(ctx)
+
+	for _, origin := range []string{"https://custom.example", "https://torrentclaw.com"} {
+		rr := httptest.NewRecorder()
+		req := httptest.NewRequest(http.MethodGet, "/health", nil)
+		req.Header.Set("Origin", origin)
+		srv.healthHandler(rr, req)
+		if got := rr.Header().Get("Access-Control-Allow-Origin"); got != origin {
+			t.Errorf("origin %q: ACAO = %q", origin, got)
+		}
+	}
+}
+
 // TestStreamServer_HLS_InvalidSessionID verifica que el hlsHandler rechaza
 // session IDs con caracteres ilegales devolviendo 404 (uniforme con sesión
 // inexistente) para no filtrar el formato aceptado a un attacker.

internal/engine/validate.go

@@ -10,3 +10,39 @@ import "regexp"
 // anything containing slashes, dots, or path separators is rejected so a
 // compromised or buggy server cannot escape hlsTmpDirRoot via os.MkdirAll.
 var validSessionID = regexp.MustCompile(`^[a-zA-Z0-9_-]{1,128}$`)
+
+// defaultCORSAllowedOrigins is the baseline of browser origins that may
+// XHR-probe `/health` and friends on the local daemon. Production hosts are
+// hardcoded; localhost on the dev port used by torrentclaw-web is included
+// so dev builds work without extra configuration. Operators may add more
+// origins via the [downloads] cors_extra_origins TOML key.
+//
+// The dev port matches `next dev -p 3030` in torrentclaw-web/package.json.
+// 127.0.0.1 is listed in addition to localhost because some browsers treat
+// them as distinct origins for CORS.
+//
+// Note: media tags (<video src>, <audio src>) do not send the Origin
+// header so they are not gated by CORS at all; this allowlist only
+// affects fetch()/XHR.
+var defaultCORSAllowedOrigins = []string{
+	"https://torrentclaw.com",
+	"https://app.torrentclaw.com",
+	"http://localhost:3030",
+	"http://127.0.0.1:3030",
+}
+
+// buildCORSAllowlist merges the default origins with any extras supplied by
+// the operator. Returned map is intended to be installed once at Listen()
+// and treated as read-only afterwards.
+func buildCORSAllowlist(extra []string) map[string]struct{} {
+	out := make(map[string]struct{}, len(defaultCORSAllowedOrigins)+len(extra))
+	for _, o := range defaultCORSAllowedOrigins {
+		out[o] = struct{}{}
+	}
+	for _, o := range extra {
+		if o != "" {
+			out[o] = struct{}{}
+		}
+	}
+	return out
+}

internal/upgrade/extract.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -85,15 +86,22 @@ func extractZip(archivePath, destDir string) (string, error) {
 
 	target := binaryName + ".exe"
 
-	for _, f := range r.File {
-		name := filepath.Base(f.Name)
+	// Resolve destDir to its absolute form once so the ZIP-slip check below
+	// can compare canonical paths instead of fragile substring matches.
+	absDest, err := filepath.Abs(destDir)
+	if err != nil {
+		return "", fmt.Errorf("resolve dest: %w", err)
+	}
 
-		// Guard against path traversal
-		if strings.Contains(f.Name, "..") {
+	for _, f := range r.File {
+		if f.FileInfo().IsDir() {
 			continue
 		}
-
-		if name != target {
+		if filepath.Base(f.Name) != target {
+			continue
+		}
+		absDst, ok := safeZipPath(f.Name, target, absDest)
+		if !ok {
 			continue
 		}
 
@@ -102,8 +110,7 @@ func extractZip(archivePath, destDir string) (string, error) {
 			return "", err
 		}
 
-		dst := filepath.Join(destDir, target)
-		out, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o755)
+		out, err := os.OpenFile(absDst, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o755)
 		if err != nil {
 			rc.Close()
 			return "", err
@@ -116,8 +123,41 @@ func extractZip(archivePath, destDir string) (string, error) {
 		}
 		out.Close()
 		rc.Close()
-		return dst, nil
+		return absDst, nil
 	}
 
 	return "", fmt.Errorf("binary %q not found in archive", target)
 }
+
+// safeZipPath validates that a ZIP entry name is safe to extract under
+// absDest, then returns the absolute destination path (always
+// absDest/target, never the raw entry name — we still only extract files
+// matched by Base name).
+//
+// Rejected: absolute paths, paths that resolve to "..", paths containing
+// a "../" or "..\\" component, and any entry whose final destination
+// would land outside absDest. The check uses path.Clean on the entry's
+// native separator (ZIP uses forward slashes by spec, but some authors
+// emit backslashes — we treat both as separators here so a hostile entry
+// on Linux can't bypass the substring scan).
+func safeZipPath(entryName, target, absDest string) (string, bool) {
+	// Normalise both separators to "/" so the check works on Linux too,
+	// where filepath.Separator is "/" and a hostile "..\\foo" string is
+	// otherwise treated as a single filename component by filepath.Clean.
+	normalised := strings.ReplaceAll(entryName, `\`, "/")
+	cleaned := path.Clean(normalised)
+	if cleaned == ".." ||
+		strings.HasPrefix(cleaned, "../") ||
+		strings.Contains(cleaned, "/../") ||
+		path.IsAbs(cleaned) {
+		return "", false
+	}
+	absDst, err := filepath.Abs(filepath.Join(absDest, target))
+	if err != nil {
+		return "", false
+	}
+	if !strings.HasPrefix(absDst+string(filepath.Separator), absDest+string(filepath.Separator)) {
+		return "", false
+	}
+	return absDst, true
+}

internal/upgrade/upgrade_test.go

@@ -1085,3 +1085,40 @@ func TestDownloadSetsUserAgent(t *testing.T) {
 		t.Errorf("User-Agent = %q, want 'unarr-updater'", gotUA)
 	}
 }
+
+func TestSafeZipPath(t *testing.T) {
+	dest := t.TempDir()
+	absDest, err := filepath.Abs(dest)
+	if err != nil {
+		t.Fatalf("abs dest: %v", err)
+	}
+
+	// Names that must extract successfully.
+	good := []string{
+		"unarr.exe",
+		"bin/unarr.exe",
+		"./unarr.exe",
+		"folder/sub/unarr.exe",
+	}
+	for _, name := range good {
+		if _, ok := safeZipPath(name, "unarr.exe", absDest); !ok {
+			t.Errorf("safeZipPath(%q) = ok:false, want ok:true", name)
+		}
+	}
+
+	// Names that must be rejected for path-traversal reasons.
+	bad := []string{
+		"../unarr.exe",
+		"..",
+		"foo/../../unarr.exe",
+		"/etc/passwd",
+		"/abs/unarr.exe",
+		`..\..\windows\system32\unarr.exe`, // backslash entries that escape
+		"../../bin/unarr.exe",
+	}
+	for _, name := range bad {
+		if _, ok := safeZipPath(name, "unarr.exe", absDest); ok {
+			t.Errorf("safeZipPath(%q) = ok:true, want ok:false", name)
+		}
+	}
+}