fix(sites): SSRF hardening — validate upstream + externalUrl reject private/reserved hosts (DC-074) [glm-grade=A]

Pre-fix, an authenticated dashboard operator could call: POST /api/v1/site {domain:"evil.example.com", upstream:"10.0.0.1:80"} POST /api/v1/site/external {subdomain:"x", externalUrl:"http://192.168.1.5"} and end up with a Caddy site block that proxies PUBLIC traffic at evil.example.com to an INTERNAL host. Caddy runs on DNS2 (same network as the targets), so the SSRF lands. The pre-fix /site upstream regex /^[a-z0-9.-]+:\d{1,5}$/i only checked charset — it happily accepted 192.168.1.1:80 and 169.254.169.254:80 (AWS metadata IP). /site/external called validateURL() without blockPrivate:true, leaving the door wide open. (1) New helper validateUpstream() in fleet-validation.js — reuses resolveAndCheckAddress() (DC-068 SSRF work) to reject literal private IPv4/IPv6 (loopback / RFC1918 / link-local / CGNAT / multicast / broadcast / 0.0.0.0 / TEST-NET / benchmark ranges), resolve hostnames and reject private answers (rebinding defense), and cap port to 1..65535. Opt-in via SITES_ALLOW_PRIVATE_UPSTREAMS=true. (2) /site calls validateUpstream() BEFORE caddy.modify() — gate happens before any state mutation. Throws ValidationError with canonical [DC-074] tag and a redacted hostname audit log entry. (3) /site/external calls validateURL() (syntax only) + validateUpstream() (private-IP gate). validateURL's blockPrivate is intentionally NOT passed because it has no opt-in — that's what validateUpstream is for. (4) Tests (__tests__/routes/sites-dc074.routes.test.js, NEW, 60/60 passing): helper unit tests (format, literal IPv4/IPv6 private reject, public IP accept, hostname resolve + rebinding defense, env opt-in override), POST /site integration (10 regression payloads + public accept + opt-in + port range + charset), POST /site/external integration (8 regression payloads + public accept + DNS rebinding defense + opt-in), canonical SSRF regression proof (RFC 1918 literal IPv4 in upstream + RFC 1918 literal IPv4 in URL host), unchanged-behavior checks on isPrivateOrReservedIPv4/IPv6. Full repo suite: 2402/2402 tests in 102 suites (zero regressions). GLM-5.3 stand-in judge round 1 (deleg_384b9f53, 41.46s, 3 tool calls, MiniMax-M3 per Sami authorization 2026-08-17): A ship-first. Refs: codex-as-judge SKILL.md 'Stand-in fallback chain'. Verdict record: /root/dashcaddy-polish/.ump-verdicts/2026-08-18T22-35-00Z-dc-074-round-1-A.json
2026-08-18 15:31:07 -07:00
parent 7db152499c
commit 270e8d57e3
3 changed files with 666 additions and 2 deletions
@@ -0,0 +1,535 @@
+/**
+ * DC-074: SSRF hardening for sites.js — `/site` and `/site/external`
+ * must reject upstream hosts that resolve to private/reserved ranges
+ * BEFORE they reach the Caddyfile.
+ *
+ * Bug class: an authenticated dashboard operator could call
+ *   POST /api/v1/site        {domain: "x.example.com", upstream: "10.0.0.1:80"}
+ *   POST /api/v1/site/external {subdomain: "x", externalUrl: "http://192.168.1.5"}
+ * and end up with a Caddy site block that proxies PUBLIC traffic to an
+ * INTERNAL host. Caddy runs on DNS2 (same network as the targets), so
+ * the SSRF lands.
+ *
+ * Pre-fix: `/site`'s only upstream check was `^[a-z0-9.-]+:\d{1,5}$/i`,
+ * which accepts 192.168.1.1:80 and 169.254.169.254:80 (the AWS
+ * metadata IP) with no problem. `/site/external` used `validateURL`
+ * without `blockPrivate: true` at all.
+ *
+ * Post-fix: a new helper `validateUpstream()` in `fleet-validation.js`
+ * reuses the resolver+private-range checks fleet-validation already has
+ * for DC-068, gating Caddyfile writes behind a public-IP requirement.
+ * Opt-in via `SITES_ALLOW_PRIVATE_UPSTREAMS=true` for operators who
+ * intentionally proxy to private targets.
+ *
+ * The suite covers three layers:
+ *   1. Helper unit tests — validateUpstream with mocked DNS / literal IPs
+ *   2. Route integration tests — POST /site and POST /site/external
+ *      reject each known private range, accept public IPs and hostnames
+ *   3. Regression — pre-fix payload `10.0.0.1:80` is rejected (the
+ *      canonical SSRF regression proof)
+ */
+const express = require('express');
+const request = require('supertest');
+
+const {
+  validateUpstream,
+  isPrivateOrReservedIPv4,
+  isPrivateOrReservedIPv6,
+} = require('../../src/utilities/fleet-validation');
+
+// ---------------------------------------------------------------------------
+// Test fixtures
+// ---------------------------------------------------------------------------
+
+const LOG = () => ({ info: jest.fn(), warn: jest.fn(), error: jest.fn() });
+
+/**
+ * Build a minimal Express app that mounts /api/v1/sites with stubbed
+ * caddy/dns/buildDomain/addServiceToConfig. The stubs record every call
+ * so tests can assert the route does NOT mutate the Caddyfile when it
+ * should reject.
+ */
+function createSitesApp({ log, caddyStub, buildDomainStub, dnsStub, addServiceToConfigStub } = {}) {
+  const app = express();
+  app.use(express.json({ limit: '1mb' }));
+  const sites = require('../../routes/sites');
+  const wrap = (fn) => (req, res, next) => Promise.resolve(fn(req, res, next)).catch(next);
+  const caddy = caddyStub || {
+    read: async () => '# stub caddyfile\n',
+    modify: jest.fn(async () => ({ success: true })),
+    adminUrl: 'http://127.0.0.1:2019',
+    filePath: '/tmp/stub-Caddyfile',
+  };
+  const dns = dnsStub || {
+    universalCreateRecord: jest.fn(async () => true),
+  };
+  app.use('/api/v1', sites({
+    asyncHandler: wrap,
+    ok: (res, data) => res.json({ ok: true, ...data }),
+    successMessage: (res, msg) => res.json({ ok: true, message: msg }),
+    caddy,
+    dns,
+    fetchT: async () => ({ ok: true, json: async () => ({}) }),
+    buildDomain: buildDomainStub || ((sub) => `${sub}.example.com`),
+    addServiceToConfig: addServiceToConfigStub || jest.fn(async () => true),
+    siteConfig: { dnsServerIp: '127.0.0.1' },
+    log: log || LOG(),
+  }));
+  // JSON error middleware — must mirror the shape sites.js's production
+  // global error middleware emits so route tests can assert on it. Without
+  // this, Express's default error handler returns an HTML stack trace and
+  // res.body.error is undefined.
+  // eslint-disable-next-line no-unused-vars
+  app.use((err, req, res, next) => {
+    const status = err.statusCode || 500;
+    res.status(status).json({
+      error: err.message || 'Internal Server Error',
+      code: err.code || null,
+      field: err.field || null,
+    });
+  });
+  return { app, caddy };
+}
+
+/** Mock dns.promises.lookup to return a specific IP for any hostname.
+ *  Returns an array of `{address, family}` records since fleet-validation
+ *  calls `dns.lookup(name, {all: true})`. */
+function mockDnsLookup(map) {
+  const dns = require('dns');
+  const original = dns.promises.lookup;
+  dns.promises.lookup = async (hostname, opts) => {
+    for (const [pattern, ip] of Object.entries(map)) {
+      if (hostname === pattern || (pattern instanceof RegExp && pattern.test(hostname))) {
+        const family = ip.includes(':') ? 6 : 4;
+        return [{ address: ip, family }];
+      }
+    }
+    // Default: throw ENOTFOUND
+    const err = new Error('ENOTFOUND');
+    err.code = 'ENOTFOUND';
+    throw err;
+  };
+  return () => {
+    dns.promises.lookup = original;
+  };
+}
+
+// ---------------------------------------------------------------------------
+// 1. Helper unit tests
+// ---------------------------------------------------------------------------
+
+describe('DC-074: validateUpstream (helper)', () => {
+  let restoreDns;
+
+  beforeEach(() => {
+    delete process.env.SITES_ALLOW_PRIVATE_UPSTREAMS;
+  });
+
+  afterEach(() => {
+    if (restoreDns) restoreDns();
+    delete process.env.SITES_ALLOW_PRIVATE_UPSTREAMS;
+  });
+
+  describe('format validation', () => {
+    test('rejects empty / non-string with INVALID_UPSTREAM', async () => {
+      expect(await validateUpstream('')).toMatchObject({ ok: false, code: 'INVALID_UPSTREAM' });
+      expect(await validateUpstream(null)).toMatchObject({ ok: false, code: 'INVALID_UPSTREAM' });
+      expect(await validateUpstream(undefined)).toMatchObject({ ok: false, code: 'INVALID_UPSTREAM' });
+      expect(await validateUpstream(42)).toMatchObject({ ok: false, code: 'INVALID_UPSTREAM' });
+    });
+
+    test('rejects missing port with INVALID_UPSTREAM', async () => {
+      expect(await validateUpstream('hostonly')).toMatchObject({ ok: false, code: 'INVALID_UPSTREAM' });
+    });
+
+    test('rejects non-integer port with INVALID_PORT', async () => {
+      expect(await validateUpstream('host:abc')).toMatchObject({ ok: false, code: 'INVALID_PORT' });
+      expect(await validateUpstream('host:80.5')).toMatchObject({ ok: false, code: 'INVALID_PORT' });
+    });
+
+    test('rejects out-of-range port with INVALID_PORT', async () => {
+      expect(await validateUpstream('host:0')).toMatchObject({ ok: false, code: 'INVALID_PORT' });
+      expect(await validateUpstream('host:65536')).toMatchObject({ ok: false, code: 'INVALID_PORT' });
+      expect(await validateUpstream('host:99999999')).toMatchObject({ ok: false, code: 'INVALID_PORT' });
+      expect(await validateUpstream('host:-1')).toMatchObject({ ok: false, code: 'INVALID_PORT' });
+    });
+  });
+
+  describe('private IPv4 reject (literal)', () => {
+    const PRIVATE_V4 = [
+      ['127.0.0.1', 'loopback'],
+      ['127.255.255.1', 'loopback'],
+      ['10.0.0.1', 'RFC 1918'],
+      ['172.16.0.1', 'RFC 1918'],
+      ['192.168.1.1', 'RFC 1918'],
+      ['169.254.169.254', 'link-local'],          // AWS IMDS
+      ['100.64.0.1', 'CGNAT'],
+      ['224.0.0.1', 'multicast'],
+      ['255.255.255.255', 'broadcast'],
+      ['0.0.0.0', 'reserved'],
+    ];
+    for (const [ip, wantLabel] of PRIVATE_V4) {
+      test(`rejects ${ip} (${wantLabel})`, async () => {
+        const r = await validateUpstream(`${ip}:80`);
+        expect(r.ok).toBe(false);
+        expect(r.code).toBe('PRIVATE_IPV4');
+        expect(r.message).toMatch(new RegExp(wantLabel, 'i'));
+      });
+    }
+  });
+
+  describe('private IPv6 reject (literal)', () => {
+    test('rejects ::1 (loopback)', async () => {
+      const r = await validateUpstream('[::1]:80');
+      expect(r.ok).toBe(false);
+      expect(r.code).toBe('PRIVATE_IPV6');
+    });
+
+    test('rejects fe80::1 (link-local)', async () => {
+      const r = await validateUpstream('[fe80::1]:80');
+      expect(r.ok).toBe(false);
+      expect(r.code).toBe('PRIVATE_IPV6');
+    });
+
+    test('rejects fc00::1 (ULA)', async () => {
+      const r = await validateUpstream('[fc00::1]:80');
+      expect(r.ok).toBe(false);
+      expect(r.code).toBe('PRIVATE_IPV6');
+    });
+  });
+
+  describe('public IPs accepted (literal)', () => {
+    test('accepts 8.8.8.8', async () => {
+      const r = await validateUpstream('8.8.8.8:53');
+      expect(r.ok).toBe(true);
+      expect(r.host).toBe('8.8.8.8');
+      expect(r.port).toBe(53);
+      expect(r.family).toBe(4);
+    });
+
+    test('accepts 1.1.1.1', async () => {
+      const r = await validateUpstream('1.1.1.1:443');
+      expect(r.ok).toBe(true);
+      expect(r.port).toBe(443);
+    });
+  });
+
+  describe('hostname resolve', () => {
+    test('accepts hostname that resolves to public IP', async () => {
+      restoreDns = mockDnsLookup({ 'public.example.com': '8.8.8.8' });
+      const r = await validateUpstream('public.example.com:443');
+      expect(r.ok).toBe(true);
+      expect(r.resolvedIp).toBe('8.8.8.8');
+      expect(r.family).toBe(4);
+    });
+
+    test('rejects hostname that resolves to private IP (DNS rebinding defense)', async () => {
+      restoreDns = mockDnsLookup({ 'evil.example.com': '10.0.0.5' });
+      const r = await validateUpstream('evil.example.com:80');
+      expect(r.ok).toBe(false);
+      expect(r.code).toBe('PRIVATE_IPV4');
+      expect(r.message).toMatch(/evil\.example\.com.*10\.0\.0\.5/);
+    });
+
+    test('rejects hostname that fails to resolve', async () => {
+      // mockDnsLookup default throws ENOTFOUND
+      const r = await validateUpstream('does-not-exist.invalid:80');
+      expect(r.ok).toBe(false);
+      expect(r.code).toMatch(/DNS_/);
+    });
+
+    test('rejects hostname with invalid charset pre-DNS', async () => {
+      const r = await validateUpstream('host with spaces:80');
+      expect(r.ok).toBe(false);
+      expect(r.code).toBe('INVALID_HOST');
+    });
+  });
+
+  describe('SITES_ALLOW_PRIVATE_UPSTREAMS opt-in', () => {
+    test('default rejects private IPs', async () => {
+      const r = await validateUpstream('10.0.0.1:80');
+      expect(r.ok).toBe(false);
+    });
+
+    test('opt-in accepts private literal IP', async () => {
+      process.env.SITES_ALLOW_PRIVATE_UPSTREAMS = 'true';
+      const r = await validateUpstream('10.0.0.1:80');
+      expect(r.ok).toBe(true);
+    });
+
+    test('opt-in accepts private DNS-resolved host', async () => {
+      process.env.SITES_ALLOW_PRIVATE_UPSTREAMS = 'true';
+      restoreDns = mockDnsLookup({ 'internal.example.com': '10.0.0.5' });
+      const r = await validateUpstream('internal.example.com:80');
+      expect(r.ok).toBe(true);
+    });
+
+    test('explicit allowPrivate:false overrides env opt-in (programmatic guard)', async () => {
+      process.env.SITES_ALLOW_PRIVATE_UPSTREAMS = 'true';
+      const r = await validateUpstream('10.0.0.1:80', { allowPrivate: false });
+      expect(r.ok).toBe(false);
+      expect(r.code).toBe('PRIVATE_IPV4');
+    });
+  });
+});
+
+// ---------------------------------------------------------------------------
+// 2. Route integration tests — POST /site
+// ---------------------------------------------------------------------------
+
+describe('DC-074: POST /api/v1/site — SSRF hardening', () => {
+  let restoreDns;
+  let caddyStub;
+
+  beforeEach(() => {
+    delete process.env.SITES_ALLOW_PRIVATE_UPSTREAMS;
+    caddyStub = {
+      read: async () => '# stub caddyfile\n',
+      modify: jest.fn(async () => ({ success: true })),
+      adminUrl: 'http://127.0.0.1:2019',
+      filePath: '/tmp/stub-Caddyfile',
+    };
+  });
+
+  afterEach(() => {
+    if (restoreDns) restoreDns();
+    delete process.env.SITES_ALLOW_PRIVATE_UPSTREAMS;
+  });
+
+  const REGRESSION_CASES = [
+    ['10.0.0.1:80',          'PRIVATE_IPV4'],
+    ['172.16.0.1:80',        'PRIVATE_IPV4'],
+    ['192.168.1.1:80',       'PRIVATE_IPV4'],
+    ['127.0.0.1:80',         'PRIVATE_IPV4'],
+    ['169.254.169.254:80',   'PRIVATE_IPV4'],   // AWS IMDS
+    ['100.64.0.1:80',        'PRIVATE_IPV4'],   // CGNAT
+    ['224.0.0.1:80',         'PRIVATE_IPV4'],   // multicast
+    ['0.0.0.0:80',           'PRIVATE_IPV4'],   // reserved
+    ['[::1]:80',             'PRIVATE_IPV6'],
+    ['[fc00::1]:80',         'PRIVATE_IPV6'],
+  ];
+
+  for (const [upstream, wantCode] of REGRESSION_CASES) {
+    test(`rejects upstream="${upstream}" with code=${wantCode}`, async () => {
+      const { app } = createSitesApp({ caddyStub });
+      const res = await request(app)
+        .post('/api/v1/site')
+        .send({ domain: 'evil.example.com', upstream });
+      expect(res.status).toBe(400);
+      expect(res.body.error).toMatch(/\[DC-074\]/);
+      expect(res.body.error).toMatch(/SITES_ALLOW_PRIVATE_UPSTREAMS/);
+      // caddy.modify() must NOT have been called (gate happens before write)
+      expect(caddyStub.modify).not.toHaveBeenCalled();
+    });
+  }
+
+  test('rejects DNS-resolved private IP (rebinding defense)', async () => {
+    restoreDns = mockDnsLookup({ 'looks-public.example.com': '10.0.0.5' });
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site')
+      .send({ domain: 'evil.example.com', upstream: 'looks-public.example.com:80' });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/10\.0\.0\.5/);
+    expect(caddyStub.modify).not.toHaveBeenCalled();
+  });
+
+  test('accepts public literal IP', async () => {
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site')
+      .send({ domain: 'new.example.com', upstream: '8.8.8.8:80' });
+    expect(res.status).toBe(200);
+    expect(caddyStub.modify).toHaveBeenCalledTimes(1);
+  });
+
+  test('accepts hostname resolving to public IP', async () => {
+    restoreDns = mockDnsLookup({ 'real.example.com': '8.8.8.8' });
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site')
+      .send({ domain: 'new.example.com', upstream: 'real.example.com:80' });
+    expect(res.status).toBe(200);
+    expect(caddyStub.modify).toHaveBeenCalledTimes(1);
+  });
+
+  test('SITES_ALLOW_PRIVATE_UPSTREAMS=true opts in for private literal', async () => {
+    process.env.SITES_ALLOW_PRIVATE_UPSTREAMS = 'true';
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site')
+      .send({ domain: 'lab.example.com', upstream: '10.0.0.1:80' });
+    expect(res.status).toBe(200);
+    expect(caddyStub.modify).toHaveBeenCalledTimes(1);
+  });
+
+  test('SITES_ALLOW_PRIVATE_UPSTREAMS=true opts in for private-resolved hostname', async () => {
+    process.env.SITES_ALLOW_PRIVATE_UPSTREAMS = 'true';
+    restoreDns = mockDnsLookup({ 'internal.lan': '10.0.0.5' });
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site')
+      .send({ domain: 'lab.example.com', upstream: 'internal.lan:80' });
+    expect(res.status).toBe(200);
+  });
+
+  test('rejects out-of-range port without invoking private-IP check', async () => {
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site')
+      .send({ domain: 'new.example.com', upstream: '8.8.8.8:99999' });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/INVALID_PORT|\[DC-074\]/);
+    expect(caddyStub.modify).not.toHaveBeenCalled();
+  });
+
+  test('rejects upstream with spaces (charset) without invoking private-IP check', async () => {
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site')
+      .send({ domain: 'new.example.com', upstream: 'not a host:80' });
+    expect(res.status).toBe(400);
+    expect(caddyStub.modify).not.toHaveBeenCalled();
+  });
+});
+
+// ---------------------------------------------------------------------------
+// 3. Route integration tests — POST /site/external
+// ---------------------------------------------------------------------------
+
+describe('DC-074: POST /api/v1/site/external — SSRF hardening', () => {
+  let restoreDns;
+  let caddyStub;
+
+  beforeEach(() => {
+    delete process.env.SITES_ALLOW_PRIVATE_UPSTREAMS;
+    caddyStub = {
+      read: async () => '# stub caddyfile\n',
+      modify: jest.fn(async () => ({ success: true })),
+      adminUrl: 'http://127.0.0.1:2019',
+      filePath: '/tmp/stub-Caddyfile',
+    };
+  });
+
+  afterEach(() => {
+    if (restoreDns) restoreDns();
+    delete process.env.SITES_ALLOW_PRIVATE_UPSTREAMS;
+  });
+
+  const REGRESSION_CASES = [
+    'http://10.0.0.1',
+    'http://192.168.1.1',
+    'http://127.0.0.1',
+    'http://169.254.169.254',     // AWS IMDS via URL form
+    'http://100.64.0.1',          // CGNAT — caught by validateUpstream defense-in-depth, not validateURL
+    'http://0.0.0.0',
+    'http://[::1]',
+    'http://[fc00::1]',
+  ];
+
+  for (const externalUrl of REGRESSION_CASES) {
+    test(`rejects externalUrl="${externalUrl}"`, async () => {
+      const { app } = createSitesApp({ caddyStub });
+      const res = await request(app)
+        .post('/api/v1/site/external')
+        .send({ subdomain: 'ext', externalUrl });
+      // 400 from validateURL OR from validateUpstream — either path closes the gate.
+      expect(res.status).toBe(400);
+      expect(caddyStub.modify).not.toHaveBeenCalled();
+    });
+  }
+
+  test('rejects DNS-resolved private IP', async () => {
+    restoreDns = mockDnsLookup({ 'looks-public.example.com': '10.0.0.5' });
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site/external')
+      .send({ subdomain: 'ext', externalUrl: 'http://looks-public.example.com' });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/\[DC-074\]|Private URLs/);
+    expect(caddyStub.modify).not.toHaveBeenCalled();
+  });
+
+  test('accepts externalUrl with public hostname', async () => {
+    restoreDns = mockDnsLookup({ 'api.example.com': '8.8.8.8' });
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site/external')
+      .send({ subdomain: 'ext', externalUrl: 'http://api.example.com' });
+    expect(res.status).toBe(200);
+    expect(caddyStub.modify).toHaveBeenCalledTimes(1);
+  });
+
+  test('accepts externalUrl with public literal IP', async () => {
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site/external')
+      .send({ subdomain: 'ext', externalUrl: 'http://8.8.8.8' });
+    expect(res.status).toBe(200);
+  });
+
+  test('SITES_ALLOW_PRIVATE_UPSTREAMS=true opts in for private externalUrl', async () => {
+    process.env.SITES_ALLOW_PRIVATE_UPSTREAMS = 'true';
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site/external')
+      .send({ subdomain: 'ext', externalUrl: 'http://10.0.0.5' });
+    expect(res.status).toBe(200);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// 4. Regression — pre-fix payload (the canonical SSRF regression proof)
+// ---------------------------------------------------------------------------
+
+describe('DC-074: regression — pre-fix payloads are now rejected', () => {
+  test('the canonical SSRF payload `10.0.0.1:80` is rejected at the route layer', async () => {
+    const caddyStub = {
+      read: async () => '',
+      modify: jest.fn(async () => ({ success: true })),
+      adminUrl: 'http://127.0.0.1:2019',
+      filePath: '/tmp/stub-Caddyfile',
+    };
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site')
+      .send({ domain: 'evil.attacker.com', upstream: '10.0.0.1:80' });
+    expect(res.status).toBe(400);
+    // Pre-fix this payload would have been accepted, the regex happily
+    // matches `[a-z0-9.-]+:\d{1,5}` against `10.0.0.1:80`, and a Caddy
+    // site block would have been written that proxied public HTTPS
+    // traffic at `evil.attacker.com` to the internal 10.0.0.1:80.
+    expect(caddyStub.modify).not.toHaveBeenCalled();
+  });
+
+  test('the canonical SSRF payload `http://192.168.1.5` is rejected at the external endpoint', async () => {
+    const caddyStub = {
+      read: async () => '',
+      modify: jest.fn(async () => ({ success: true })),
+      adminUrl: 'http://127.0.0.1:2019',
+      filePath: '/tmp/stub-Caddyfile',
+    };
+    const { app } = createSitesApp({ caddyStub });
+    const res = await request(app)
+      .post('/api/v1/site/external')
+      .send({ subdomain: 'ext', externalUrl: 'http://192.168.1.5' });
+    expect(res.status).toBe(400);
+    expect(caddyStub.modify).not.toHaveBeenCalled();
+  });
+});
+
+// ---------------------------------------------------------------------------
+// 5. Sanity — fleet-validation helper exports still work as before
+// ---------------------------------------------------------------------------
+
+describe('DC-074: fleet-validation helpers still exported and unchanged behavior', () => {
+  test('isPrivateOrReservedIPv4 still detects the same set as before', () => {
+    expect(isPrivateOrReservedIPv4('10.0.0.1').isPrivate).toBe(true);
+    expect(isPrivateOrReservedIPv4('8.8.8.8').isPrivate).toBe(false);
+  });
+
+  test('isPrivateOrReservedIPv6 still detects the same set as before', () => {
+    expect(isPrivateOrReservedIPv6('::1').isPrivate).toBe(true);
+    expect(isPrivateOrReservedIPv6('2001:4860:4860::8888').isPrivate).toBe(false);
+  });
+});