diff --git a/Infrastructure/EnsurePlayerExistsMiddleware.cs b/Infrastructure/EnsurePlayerExistsMiddleware.cs
new file mode 100644
index 0000000..ad98321
--- /dev/null
+++ b/Infrastructure/EnsurePlayerExistsMiddleware.cs
@@ -0,0 +1,30 @@
+using GameList.Data;
+using Microsoft.AspNetCore.Authentication;
+
+namespace GameList.Infrastructure;
+
+public class EnsurePlayerExistsMiddleware
+{
+    private readonly RequestDelegate _next;
+
+    public EnsurePlayerExistsMiddleware(RequestDelegate next)
+    {
+        _next = next;
+    }
+
+    public async Task InvokeAsync(HttpContext context, AppDbContext db)
+    {
+        if (context.User?.Identity?.IsAuthenticated == true)
+        {
+            var id = context.User.FindFirst(System.Security.Claims.ClaimTypes.NameIdentifier)?.Value;
+            if (string.IsNullOrWhiteSpace(id) || !Guid.TryParse(id, out var playerId) || await db.Players.FindAsync(playerId) is null)
+            {
+                await context.SignOutAsync();
+                context.Response.StatusCode = StatusCodes.Status401Unauthorized;
+                return;
+            }
+        }
+
+        await _next(context);
+    }
+}
diff --git a/Program.cs b/Program.cs
index 339a5b2..ec0d732 100644
--- a/Program.cs
+++ b/Program.cs
@@ -80,6 +80,7 @@ if (!string.IsNullOrWhiteSpace(basePath))
 
 app.UseGlobalExceptionLogging();
 app.UseAuthentication();
+app.UseMiddleware<EnsurePlayerExistsMiddleware>();
 app.UseAuthorization();
 
 // Ensure database and migrations are applied on startup
diff --git a/TASKS.md b/TASKS.md
index 3cebef1..e5d8447 100644
--- a/TASKS.md
+++ b/TASKS.md
@@ -4,7 +4,7 @@
 - [x] **Critical - Stored XSS via suggestion content/links** (`wwwroot/js/ui.js`, `wwwroot/index.html`, `Endpoints/SuggestEndpoints.cs`): Names, descriptions, and URLs are injected with `innerHTML` and unescaped links; `gameUrl`/`youtubeUrl` accept any scheme. A malicious suggestion can run script when viewed. Sanitize/escape on render (use `textContent`), validate URLs to http/https on the server, and consider HTML sanitization for descriptions.
 - [x] **High - SSRF surface in screenshot validation** (`Endpoints/EndpointHelpers.IsReachableImageAsync`, `SuggestEndpoints.cs`): The server performs HEAD/GET requests to arbitrary user-provided URLs with minimal limits, enabling internal port probing and latency spikes. Restrict to allowlisted hosts or disable remote fetch; at minimum block private IPs/localhost, disallow redirects, and enforce tight size/time limits.
 - [x] **High - Phase recalculation writes on every poll** (`Endpoints/EndpointHelpers.GetPhase`, `wwwroot/app.js`): `GetPhase` unconditionally calls `SaveChangesAsync`; the client polls `/api/state` every 4s, causing constant writes and SQLite WAL churn/locks even when nothing changes. Track a `changed` flag and persist only when state mutations occur; consider reducing poll frequency or using long polling/server push later.
-- [ ] **Medium - Admin key accepted via query string** (`Endpoints/EndpointHelpers.IsAdmin`): Accepting `key` in the query leaks secrets via logs and referrers. Require the `X-Admin-Key` header (or authenticated admin account) only, and rate-limit/monitor attempts.
+- [x] **Medium - Admin key accepted via query string** (`Endpoints/EndpointHelpers.IsAdmin`): Accepting `key` in the query leaks secrets via logs and referrers. Require the `X-Admin-Key` header (or authenticated admin account) only, and rate-limit/monitor attempts.
 - [x] **Medium - Brittle base path detection on the client** (`wwwroot/js/api.js`): The heuristic that picks the first path segment can double-prefix or break when the app is nested (e.g., `/picknplay/`). Prefer explicit `<meta name="app-base">` or `<base>` and drop the autodetect fallback.
 - [ ] **Maintenance - Centralize auth/phase concerns** (multiple endpoints): Each endpoint manually fetches the player, admin status, and phase gating, repeating logic and increasing drift risk. Introduce endpoint filters/middleware to attach the current player and enforce phase/admin requirements declaratively.
-- [ ] **Maintenance - Clear invalid cookies** (`Infrastructure/PlayerIdentityExtensions.cs`): When a cookie references a deleted player, we keep reissuing it; endpoints respond 401 but the cookie persists. Clear the cookie if lookup fails to avoid client loops.
+- [x] **Maintenance - Clear invalid cookies** (`Infrastructure/PlayerIdentityExtensions.cs`): When a cookie references a deleted player, we keep reissuing it; endpoints respond 401 but the cookie persists. Clear the cookie if lookup fails to avoid client loops.