Merge pull request 'security: stop trusting the leftmost x-forwarded-for for rate limits and abuse quotas (FRE-371)' (#1) from agent-security-engineer/freno-dev:freno-dev/FRE-371-trusted-client-ip-clean into master

Reviewed-on: #1

src/routes/api/the-nook/report.test.ts

@@ -10,6 +10,8 @@ import { describe, expect, it, mock, beforeEach } from "bun:test";
 
 const sentEmails: { to: string; subject: string; html: string }[] = [];
 const tokenAnswers: { allowed: boolean; retryAfterSec?: number }[] = [];
+/** Every rate-limit key the route derived, in order. */
+const rateKeys: string[] = [];
 
 mock.module("~/server/email", () => ({
   default: async (to: string, subject: string, html: string) => {
@@ -19,7 +21,10 @@ mock.module("~/server/email", () => ({
 }));
 
 mock.module("~/server/bug-report-rate-limit", () => ({
-  takeBugReportToken: () => tokenAnswers.shift() ?? { allowed: true }
+  takeBugReportToken: (key: string) => {
+    rateKeys.push(key);
+    return tokenAnswers.shift() ?? { allowed: true };
+  }
 }));
 
 const { POST } = await import("./report");
@@ -72,6 +77,7 @@ describe("POST /api/the-nook/report", () => {
   beforeEach(() => {
     sentEmails.length = 0;
     tokenAnswers.length = 0;
+    rateKeys.length = 0;
   });
 
   it("emails the owner a report containing the snapshot, escaped", async () => {
@@ -133,10 +139,49 @@ describe("POST /api/the-nook/report", () => {
 
   it("still succeeds when no fingerprint header exists", async () => {
     const res = await POST(
-      request(validPayload, { "x-forwarded-for": "203.0.113.9, 10.0.0.1" })
+      request(validPayload, {
+        "cf-connecting-ip": "203.0.113.9",
+        "x-forwarded-for": "203.0.113.9, 10.0.0.1"
+      })
     );
     expect(res.status).toBe(200);
     expect(sentEmails).toHaveLength(1);
+    // The quota key is the Cloudflare-recorded client, not a header hop the
+    // sender chose.
+    expect(rateKeys).toEqual(["203.0.113.9"]);
+  });
+
+  it("a rotating leftmost x-forwarded-for does not mint a fresh quota key", async () => {
+    // FRE-371: the old read keyed on the leftmost hop, which the sender
+    // controls outright — one scripted loop with a rotating header had
+    // unlimited reports. With the same Cloudflare-recorded client and a
+    // different spoofed prefix per request, the key must be stable.
+    for (const spoof of ["1.1.1.1", "2.2.2.2", "3.3.3.3"]) {
+      const res = await POST(
+        request(validPayload, {
+          "cf-connecting-ip": "203.0.113.9",
+          "x-forwarded-for": `${spoof}, 203.0.113.9, 10.0.0.1`
+        })
+      );
+      expect(res.status).toBe(200);
+    }
+
+    expect(rateKeys).toEqual([
+      "203.0.113.9",
+      "203.0.113.9",
+      "203.0.113.9"
+    ]);
+  });
+
+  it("keys on the rightmost-minus-one hop when Cloudflare's header is absent", async () => {
+    const res = await POST(
+      request(validPayload, {
+        "x-forwarded-for": "6.6.6.6, 203.0.113.9, 10.0.0.1"
+      })
+    );
+    expect(res.status).toBe(200);
+    // Never the leftmost (sender-chosen) hop.
+    expect(rateKeys).toEqual(["203.0.113.9"]);
   });
 
   it("delivers the landing page's beta request with only the email", async () => {

src/routes/api/the-nook/report.ts

@@ -3,6 +3,7 @@ import { z } from "zod";
 import sendEmail from "~/server/email";
 import { CONTACT_RECIPIENT_EMAIL } from "~/lib/contact-config";
 import { takeBugReportToken } from "~/server/bug-report-rate-limit";
+import { resolveTrustedClientIp } from "~/server/trusted-client-ip";
 import { json, error } from "./_lib";
 
 /**
@@ -103,10 +104,9 @@ export async function POST(event: APIEvent): Promise<Response> {
   )
     .trim()
     .toLowerCase();
-  const forwarded = event.request.headers.get("x-forwarded-for");
-  const rateKey =
-    fingerprint ||
-    (forwarded ? forwarded.split(",")[0]!.trim() : "unknown");
+  // FRE-371: the IP fallback must be the spoof-resistant read — a rotating
+  // leftmost x-forwarded-for used to mint unlimited report quota.
+  const rateKey = fingerprint || resolveTrustedClientIp(event);
   const token = takeBugReportToken(rateKey);
   if (!token.allowed) {
     return new Response(JSON.stringify({ error: "Too many reports" }), {