fix(security): resolve rate-limiting IP spoofing and eviction bypass

app/api/auth/route.ts

@@ -5,20 +5,14 @@
 
 import { NextRequest, NextResponse } from 'next/server';
 import { authenticate, isProtected } from '@/lib/auth';
-import { checkRateLimit } from '@/lib/rate-limit';
+import { checkRateLimit, getClientIp } from '@/lib/rate-limit';
 
 /** Tight limit for auth attempts — 10 per minute per IP. */
 const AUTH_RPM = 10;
 
 export async function POST(request: NextRequest) {
   // ── Rate limiting (brute-force protection) ──────────
-  // Security: Prioritize x-real-ip (set by trusted reverse proxies like nginx/Traefik)
-  // over x-forwarded-for which can be spoofed by clients.
-  // Note: request.ip was removed in Next.js 15+.
-  const ip =
-    request.headers.get('x-real-ip') ??
-    request.headers.get('x-forwarded-for')?.split(',')[0].trim() ??
-    'unknown';
+  const ip = getClientIp(request);
   const { success } = checkRateLimit(`auth:${ip}`, AUTH_RPM);
 
   if (!success) {

app/api/exif/[id]/route.ts

@@ -9,7 +9,7 @@ import { NextRequest, NextResponse } from 'next/server';
 import { immich } from '@/lib/immich';
 import { decodeAssetId } from '@/lib/tokens';
 import { getConfig } from '@/lib/config';
-import { checkRateLimit } from '@/lib/rate-limit';
+import { checkRateLimit, getClientIp } from '@/lib/rate-limit';
 
 export async function GET(request: NextRequest, { params }: { params: Promise<{ id: string }> }) {
   const config = getConfig();
@@ -20,12 +20,7 @@ export async function GET(request: NextRequest, { params }: { params: Promise<{
   }
 
   // ── Rate limiting ──────────────────────────────────
-  // Security: Prioritize x-real-ip (set by trusted reverse proxies like nginx/Traefik)
-  // over x-forwarded-for which can be spoofed by clients.
-  const ip =
-    request.headers.get('x-real-ip') ??
-    request.headers.get('x-forwarded-for')?.split(',')[0].trim() ??
-    'unknown';
+  const ip = getClientIp(request);
   const { success, resetAt } = checkRateLimit(`exif:${ip}`, config.rateLimitRpm);
 
   if (!success) {

app/api/image/[id]/route.ts

@@ -11,7 +11,7 @@ import { NextRequest, NextResponse } from 'next/server';
 import { immich, ImageSize } from '@/lib/immich';
 import { decodeAssetId } from '@/lib/tokens';
 import { getConfig } from '@/lib/config';
-import { checkRateLimit } from '@/lib/rate-limit';
+import { checkRateLimit, getClientIp } from '@/lib/rate-limit';
 
 const VALID_SIZES: ImageSize[] = ['thumbnail', 'preview', 'original'];
 
@@ -26,13 +26,7 @@ function widthToSize(w: number): ImageSize {
 
 export async function GET(request: NextRequest, { params }: { params: Promise<{ id: string }> }) {
   // ── Rate limiting ──────────────────────────────────
-  // Security: Prioritize x-real-ip (set by trusted reverse proxies like nginx/Traefik)
-  // over x-forwarded-for which can be spoofed by clients.
-  // Note: request.ip was removed in Next.js 15+.
-  const ip =
-    request.headers.get('x-real-ip') ??
-    request.headers.get('x-forwarded-for')?.split(',')[0].trim() ??
-    'unknown';
+  const ip = getClientIp(request);
   const { success, remaining, resetAt } = checkRateLimit(ip, getConfig().rateLimitRpm);
 
   if (!success) {

lib/rate-limit.ts

@@ -9,6 +9,16 @@
  * multiple nodes, a persistent store like Redis would be required.
  */
 
+import { NextRequest } from 'next/server';
+
+export function getClientIp(request: NextRequest): string {
+  return (
+    request.headers.get('x-real-ip') ??
+    request.headers.get('x-forwarded-for')?.split(',')[0].trim() ??
+    'unknown'
+  );
+}
+
 interface RateLimitEntry {
   count: number;
   expiresAt: number;
@@ -32,15 +42,6 @@ function cleanup() {
   }
 }
 
-/**
- * Evict oldest entry when store is at capacity (FIFO).
- */
-function evictIfFull() {
-  if (store.size < MAX_STORE_ENTRIES) return;
-  const firstKey = store.keys().next().value;
-  if (firstKey) store.delete(firstKey);
-}
-
 /**
  * Check if a request should be allowed.
  * @param ip - Client IP address
@@ -61,7 +62,10 @@ export function checkRateLimit(
 
   // New window or expired
   if (!entry || now > entry.expiresAt) {
-    evictIfFull();
+    if (store.size >= MAX_STORE_ENTRIES) {
+      // Store is completely full with active IPs -> block to prevent memory exhaustion & rate limit bypass
+      return { success: false, remaining: 0, resetAt: now + windowMs };
+    }
     const resetAt = now + windowMs;
     store.set(key, { count: 1, expiresAt: resetAt });
     return { success: true, remaining: maxRpm - 1, resetAt };