fix(backend): set multer's fieldArrayIndexLimit to actually close CVE-2026-82333

The advisory is explicit that the 2.3.0 version bump alone doesn't
remediate the array-index DoS — an app must also set
limits.fieldArrayIndexLimit. Set it on every multer instance, sized to
what each route's form actually needs.

backend/__tests__/routes/publicContracts.test.js

@@ -25,14 +25,18 @@ process.env.STORAGE_PATH = path.join(tmpDir, 'storage');
 fs.mkdirSync(process.env.STORAGE_PATH, { recursive: true });
 process.env.JWT_SECRET = process.env.JWT_SECRET || 'crm-route-test-secret';
 
+const express = require('express');
+const cookieParser = require('cookie-parser');
 const request = require('supertest');
 const { bootCrmDb, seedMinimal, createPublicToken, buildRouteApp } = require('../integration/helpers/crmDb');
 const tokenGuards = require('../../src/utils/publicTokenGuards');
+const { errorHandler } = require('../../src/middleware/errorHandler');
 
 describe('publicContracts routes', () => {
   let db;
   let cleanup;
   let app;
+  let appWithErrorHandler;
   let customerId;
   let contractId;
 
@@ -51,6 +55,17 @@ describe('publicContracts routes', () => {
     contractId = inserted[0]?.id ?? inserted[0];
 
     app = buildRouteApp('/api/public/contracts', require('../../src/routes/publicContracts'));
+
+    // A second app instance wired to the REAL production error handler
+    // (buildRouteApp's is a simplified stand-in that only reads
+    // err.statusCode/err.status, which a bare MulterError doesn't set).
+    // Used below to verify the actual 4xx contract end-to-end, not just
+    // that multer aborted the request.
+    appWithErrorHandler = express();
+    appWithErrorHandler.use(express.json());
+    appWithErrorHandler.use(cookieParser());
+    appWithErrorHandler.use('/api/public/contracts', require('../../src/routes/publicContracts'));
+    appWithErrorHandler.use(errorHandler);
   }, 120000);
 
   afterAll(async () => {
@@ -131,6 +146,40 @@ describe('publicContracts routes', () => {
         .attach('file', Buffer.from('%PDF-1.4 fake'), 'signed.pdf');
       expect(res.status).toBe(404);
     });
+
+    // CVE-2026-82333 regression (#1374 follow-up): multer 2.3.0 added an
+    // opt-in `fieldArrayIndexLimit` that must be set to actually close the
+    // field-parser DoS — the version bump alone does nothing. This route is
+    // unauthenticated (token-in-URL only), so it's the sharpest place to
+    // prove a crafted request with an oversized array-index field name
+    // (`evil[999999999]`) is rejected rather than accepted or left to hang.
+    it('rejects a multipart request with an oversized array-index field name', async () => {
+      const token = await createPublicToken(db, 'contract_action_tokens', {
+        contract_id: contractId,
+      });
+      const res = await request(app)
+        .post(`/api/public/contracts/${token}/upload-signed-pdf`)
+        .field('evil[999999999]', 'x')
+        .attach('file', Buffer.from('%PDF-1.4 fake'), 'signed.pdf');
+      // multer aborts the request before the handler runs; buildRouteApp's
+      // generic error handler falls back to 500 for a bare MulterError
+      // (see appWithErrorHandler test below for the real 4xx contract), so
+      // here we only assert the upload was NOT accepted/processed.
+      expect(res.status).toBeGreaterThanOrEqual(400);
+      expect(res.body.error).not.toBe(undefined);
+    });
+
+    it('maps the oversized array-index rejection to a 400 through the real error handler', async () => {
+      const token = await createPublicToken(db, 'contract_action_tokens', {
+        contract_id: contractId,
+      });
+      const res = await request(appWithErrorHandler)
+        .post(`/api/public/contracts/${token}/upload-signed-pdf`)
+        .field('evil[999999999]', 'x')
+        .attach('file', Buffer.from('%PDF-1.4 fake'), 'signed.pdf');
+      expect(res.status).toBe(400);
+      expect(res.body.code).toBe('VALIDATION_ERROR');
+    });
   });
 
   describe('GET /:token/pdf', () => {

backend/src/config/multerConfig.js

@@ -120,7 +120,14 @@ const createPhotoUploader = (options = {}) => {
       files: options.maxFiles || 2000,
       fieldSize: 10 * 1024 * 1024,
       parts: 10000,
-      headerPairs: 2000
+      headerPairs: 2000,
+      // CVE-2026-82333: no preset in this factory is currently wired up to
+      // a route (nothing imports createPhotoUploader et al. — routes build
+      // their own multer instances directly), but every preset gets the
+      // limit anyway so it can't be adopted later without it. None of the
+      // uploaders this factory builds have a legitimate use for
+      // array-indexed field names.
+      fieldArrayIndexLimit: 0
     },
     fileFilter: createFileFilter(ALLOWED_TYPES.media, {
       validateMagicNumbers: true
@@ -146,7 +153,8 @@ const createLogoUploader = (options = {}) => {
       }
     }),
     limits: {
-      fileSize: options.maxSize || SIZE_LIMITS.medium
+      fileSize: options.maxSize || SIZE_LIMITS.medium,
+      fieldArrayIndexLimit: 0 // CVE-2026-82333 — see createPhotoUploader comment
     },
     fileFilter: createFileFilter(ALLOWED_TYPES.logos, {
       skipMagicValidation: ['image/svg+xml']
@@ -172,7 +180,8 @@ const createFaviconUploader = (options = {}) => {
       }
     }),
     limits: {
-      fileSize: options.maxSize || SIZE_LIMITS.small
+      fileSize: options.maxSize || SIZE_LIMITS.small,
+      fieldArrayIndexLimit: 0 // CVE-2026-82333 — see createPhotoUploader comment
     },
     fileFilter: createFileFilter(ALLOWED_TYPES.favicons, {
       skipMagicValidation: ['image/x-icon', 'image/vnd.microsoft.icon']
@@ -194,7 +203,8 @@ const createGalleryUploader = (destDir, options = {}) => {
     dest: destDir,
     limits: {
       fileSize: options.maxSize || SIZE_LIMITS.large,
-      files: options.maxFiles || 10
+      files: options.maxFiles || 10,
+      fieldArrayIndexLimit: 0 // CVE-2026-82333 — see createPhotoUploader comment
     },
     fileFilter: createFileFilter(ALLOWED_TYPES.photos)
   };

backend/src/middleware/errorHandler.js

@@ -93,6 +93,16 @@ const handleKnownErrors = (err) => {
     return new ValidationError('Unexpected file field');
   }
 
+  // CVE-2026-82333: multer 2.3.0's fieldArrayIndexLimit rejects multipart
+  // field names with an oversized bracket array index (e.g. `a[99999999]`)
+  // before the DoS-prone field parser runs. Without this mapping the
+  // resulting MulterError has no .statusCode/.status and falls through to
+  // a 500 here, so map it to a proper 400 like the other multer limits.
+  if (err.code === 'LIMIT_FIELD_ARRAY_INDEX') {
+    const { ValidationError } = require('../utils/errors');
+    return new ValidationError('Field name array index too large');
+  }
+
   return err;
 };
 

backend/src/routes/adminBackup.js

@@ -202,7 +202,11 @@ const picpeakUpload = multer({
     destination: (req, file, cb) => cb(null, os.tmpdir()),
     filename: (req, file, cb) => cb(null, `picpeak-upload-${Date.now()}-${crypto.randomBytes(6).toString('hex')}.picpeak`),
   }),
-  limits: { fileSize: 5 * 1024 * 1024 * 1024 }, // 5 GB — .picpeak with photos can be large
+  // CVE-2026-82333: this route only ever consumes a single unnamed file
+  // field (`backup`) — no legitimate bracket-indexed field name (e.g.
+  // `a[0]`) exists in its form. fieldArrayIndexLimit: 0 rejects any field
+  // name using array-index syntax at all, closing multer's field-parser DoS.
+  limits: { fileSize: 5 * 1024 * 1024 * 1024, fieldArrayIndexLimit: 0 }, // 5 GB — .picpeak with photos can be large
 });
 
 // Upload + restore a .picpeak onto THIS instance. DESTRUCTIVE: full override of

backend/src/routes/adminBusinessProfile.js

@@ -109,7 +109,9 @@ const pdfLogoStorage = multer.diskStorage({
 
 const pdfLogoUpload = multer({
   storage: pdfLogoStorage,
-  limits: { fileSize: 5 * 1024 * 1024 },
+  // CVE-2026-82333: single unnamed `logo` field only — no legitimate
+  // array-indexed field names, so reject any bracket-index field name.
+  limits: { fileSize: 5 * 1024 * 1024, fieldArrayIndexLimit: 0 },
   fileFilter: (_req, file, cb) => {
     const allowed = ['image/png', 'image/jpeg', 'image/svg+xml'];
     if (allowed.includes(file.mimetype)) cb(null, true);

backend/src/routes/adminCMS.js

@@ -32,7 +32,9 @@ const pageLogoStorage = multer.diskStorage({
 
 const pageLogoUpload = multer({
   storage: pageLogoStorage,
-  limits: { fileSize: 5 * 1024 * 1024 },
+  // CVE-2026-82333: single unnamed `logo` field only — no legitimate
+  // array-indexed field names, so reject any bracket-index field name.
+  limits: { fileSize: 5 * 1024 * 1024, fieldArrayIndexLimit: 0 },
   fileFilter: (_req, file, cb) => {
     const allowed = ['image/jpeg', 'image/png', 'image/gif', 'image/svg+xml'];
     if (validateFileType(file.originalname, file.mimetype, allowed)) cb(null, true);

backend/src/routes/adminContracts.js

@@ -73,7 +73,9 @@ const signedPdfStorage = multer.diskStorage({
 
 const signedPdfUpload = multer({
   storage: signedPdfStorage,
-  limits: { fileSize: 10 * 1024 * 1024 }, // 10 MB
+  // CVE-2026-82333: single unnamed `file` field only — no legitimate
+  // array-indexed field names, so reject any bracket-index field name.
+  limits: { fileSize: 10 * 1024 * 1024, fieldArrayIndexLimit: 0 }, // 10 MB
   fileFilter: (req, file, cb) => {
     const allowed = ['application/pdf'];
     if (validateFileType(file.originalname, file.mimetype, allowed)) return cb(null, true);

backend/src/routes/adminEvents/logo.js

@@ -31,7 +31,9 @@ const eventLogoStorage = multer.diskStorage({
 
 const eventLogoUpload = multer({
   storage: eventLogoStorage,
-  limits: { fileSize: 5 * 1024 * 1024 }, // 5MB
+  // CVE-2026-82333: single unnamed `logo` field only — no legitimate
+  // array-indexed field names, so reject any bracket-index field name.
+  limits: { fileSize: 5 * 1024 * 1024, fieldArrayIndexLimit: 0 }, // 5MB
   fileFilter: (req, file, cb) => {
     const allowedMimeTypes = ['image/jpeg', 'image/png', 'image/gif', 'image/svg+xml'];
     if (validateFileType(file.originalname, file.mimetype, allowedMimeTypes)) {

backend/src/routes/adminExpenses.js

@@ -41,7 +41,10 @@ function diskUpload(subdir) {
       },
       filename: (_req, file, cb) => cb(null, `${subdir.split('/').pop()}-${Date.now()}${path.extname(file.originalname) || ''}`),
     }),
-    limits: { fileSize: 15 * 1024 * 1024 },
+    // CVE-2026-82333: both callers (`inboundUpload` → 'file', `proofUpload`
+    // → 'proof') take a single unnamed field — no legitimate array-indexed
+    // field names, so reject any bracket-index field name.
+    limits: { fileSize: 15 * 1024 * 1024, fieldArrayIndexLimit: 0 },
     fileFilter: (_req, file, cb) => (ALLOWED_MIME.includes(file.mimetype) ? cb(null, true) : cb(new Error('Only PDF, JPEG or PNG files are allowed'))),
   });
 }

backend/src/routes/adminInvoices.js

@@ -72,7 +72,9 @@ const importedInvoiceStorage = multer.diskStorage({
 });
 const importedInvoiceUpload = multer({
   storage: importedInvoiceStorage,
-  limits: { fileSize: 10 * 1024 * 1024 },
+  // CVE-2026-82333: single unnamed `pdf` field only — no legitimate
+  // array-indexed field names, so reject any bracket-index field name.
+  limits: { fileSize: 10 * 1024 * 1024, fieldArrayIndexLimit: 0 },
   fileFilter: (_req, file, cb) => {
     if (file.mimetype === 'application/pdf') cb(null, true);
     else cb(new Error('Only PDF files are allowed for imported invoices'));

backend/src/routes/adminPhotos.js

@@ -112,7 +112,12 @@ const createUpload = (maxFileSizeBytes) => multer({
     files: 2000, // Hard safety ceiling; actual limit enforced dynamically
     fieldSize: 10 * 1024 * 1024, // 10MB for non-file fields
     parts: 10000,
-    headerPairs: 2000
+    headerPairs: 2000,
+    // CVE-2026-82333: files arrive as repeated `photos` parts via
+    // multer's own .array('photos', N) — not bracket-indexed field names
+    // like `photos[0]` — so no legitimate field name uses array-index
+    // syntax at all. Reject any that do.
+    fieldArrayIndexLimit: 0
   },
   fileFilter: (req, file, cb) => {
     // req.allowedMimeTypes is populated by the middleware that runs before multer

backend/src/routes/adminSettings.js

@@ -153,7 +153,10 @@ const { validateFileType } = require('../utils/fileSecurityUtils');
 
 const upload = multer({
   storage,
-  limits: { fileSize: 5 * 1024 * 1024 }, // 5MB
+  // CVE-2026-82333: single unnamed field (`logo` or `watermarkLogo`) per
+  // route — no legitimate array-indexed field names, so reject any
+  // bracket-index field name.
+  limits: { fileSize: 5 * 1024 * 1024, fieldArrayIndexLimit: 0 }, // 5MB
   fileFilter: (req, file, cb) => {
     // Note: SVG files are excluded from magic number validation for logos
     const allowedMimeTypes = ['image/jpeg', 'image/png', 'image/gif', 'image/svg+xml'];
@@ -181,7 +184,9 @@ const faviconStorage = multer.diskStorage({
 
 const faviconUpload = multer({
   storage: faviconStorage,
-  limits: { fileSize: 2 * 1024 * 1024 }, // 2MB — roomy enough for a 512×512+ square PNG
+  // CVE-2026-82333: single unnamed `favicon` field only — no legitimate
+  // array-indexed field names, so reject any bracket-index field name.
+  limits: { fileSize: 2 * 1024 * 1024, fieldArrayIndexLimit: 0 }, // 2MB — roomy enough for a 512×512+ square PNG
   fileFilter: (req, file, cb) => {
     const allowedMimeTypes = ['image/png', 'image/x-icon', 'image/vnd.microsoft.icon'];
     const name = file.originalname.toLowerCase();

backend/src/routes/adminTransfers.js

@@ -50,7 +50,10 @@ const tempStorage = multer.diskStorage({
 function buildAdminUploader(maxSizeBytes, allowed) {
   return multer({
     storage: tempStorage,
-    limits: { fileSize: maxSizeBytes, files: ADMIN_MAX_FILES },
+    // CVE-2026-82333: files arrive as repeated `files` parts via .array(),
+    // not bracket-indexed field names like `files[0]` — no legitimate
+    // field name uses array-index syntax at all. Reject any that do.
+    limits: { fileSize: maxSizeBytes, files: ADMIN_MAX_FILES, fieldArrayIndexLimit: 0 },
     fileFilter: (req, file, cb) => {
       if (validateFileType(file.originalname, file.mimetype, allowed)) return cb(null, true);
       return cb(new Error('This file type is not allowed'));

backend/src/routes/gallery/uploads.js

@@ -77,7 +77,12 @@ router.post('/:eventId/upload', verifyGalleryAccess, denySlideshowToken, async (
       dest: tempUploadDir,
       limits: {
         fileSize: maxFileSizeBytes,
-        files: maxFilesPerUpload
+        files: maxFilesPerUpload,
+        // CVE-2026-82333: files arrive as repeated `photos` parts via
+        // .array(), not bracket-indexed field names like `photos[0]` — no
+        // legitimate field name uses array-index syntax at all. Reject any
+        // that do.
+        fieldArrayIndexLimit: 0
       },
       fileFilter: (req, file, cb) => {
         if (validateFileType(file.originalname, file.mimetype, allowedMimeTypes)) {

backend/src/routes/publicContracts.js

@@ -62,7 +62,10 @@ const signedPdfStorage = multer.diskStorage({
 
 const signedPdfUpload = multer({
   storage: signedPdfStorage,
-  limits: { fileSize: 10 * 1024 * 1024 }, // 10 MB
+  // CVE-2026-82333: single unnamed `file` field only, and this route is
+  // unauthenticated (token-only) — no legitimate array-indexed field
+  // names, so reject any bracket-index field name.
+  limits: { fileSize: 10 * 1024 * 1024, fieldArrayIndexLimit: 0 }, // 10 MB
   fileFilter: (req, file, cb) => {
     if (validateFileType(file.originalname, file.mimetype, ['application/pdf'])) return cb(null, true);
     return cb(new Error('Only PDF files are allowed'));

backend/src/routes/publicTransferUpload.js

@@ -122,7 +122,11 @@ const tempStorage = multer.diskStorage({
 function buildUploader(maxSizeBytes, allowed) {
   return multer({
     storage: tempStorage,
-    limits: { fileSize: maxSizeBytes, files: MAX_FILES_PER_UPLOAD },
+    // CVE-2026-82333: files arrive as repeated `files` parts via .array(),
+    // not bracket-indexed field names like `files[0]`, and this route is
+    // unauthenticated (token-only) — no legitimate field name uses
+    // array-index syntax at all. Reject any that do.
+    limits: { fileSize: maxSizeBytes, files: MAX_FILES_PER_UPLOAD, fieldArrayIndexLimit: 0 },
     fileFilter: (req, file, cb) => {
       if (validateFileType(file.originalname, file.mimetype, allowed)) return cb(null, true);
       return cb(new Error('This file type is not allowed'));

backend/src/routes/v1/events.js

@@ -69,7 +69,9 @@ const photoStorage = multer.diskStorage({
 });
 const buildPhotoUpload = (maxFileSizeBytes) => multer({
   storage: photoStorage,
-  limits: { fileSize: maxFileSizeBytes },
+  // CVE-2026-82333: single unnamed `photo` field only — no legitimate
+  // array-indexed field names, so reject any bracket-index field name.
+  limits: { fileSize: maxFileSizeBytes, fieldArrayIndexLimit: 0 },
   fileFilter: (_req, file, cb) => {
     if (/^image\//.test(file.mimetype)) cb(null, true);
     else cb(new Error('Only image uploads are accepted on this endpoint'));