Bug fixes (real breakage):

Newsletter nudge — was calling /api/study-account/profile (wrong endpoint, ignored subscription). Now correctly calls /api/study-account/preferences with PATCH.
Security:

Email regex — replaced the permissive [^\s@]+@[^\s@]+ pattern with a proper RFC-compliant regex in contact.js and downloads.js
Avatar magic bytes — server now checks actual PNG/JPEG/GIF/WEBP header bytes, not just the data URL prefix
Certificate rate limit — public /api/public/certificate/:token now has a 30 req/15min limiter
Session absolute TTL — admin sessions now have a 30-day hard cap; a stolen token can no longer be kept alive indefinitely by passive reads
Account lockout — 5 failed logins locks a study account for 1 hour
CSP headers — Content-Security-Policy, X-Frame-Options, X-Content-Type-Options, and Referrer-Policy headers added globally
Data integrity:

Cascade delete — deleting a study account now also removes their certificates, community posts, comments, and progress file
UX / reliability:

Escape key on modals — all 3 modal groups (study index, notes, account) now close on Escape
Display name min-length — empty spaces-only names rejected; if provided, must be ≥2 chars
Note save rate limit — 30 saves/minute per user max
Analytics fetch timeout — 5s AbortController so a hanging server doesn't block the browser indefinitely
Email validation on signup — frontend catches bad email formats before hitting the server
Cleanup:

Deduplicated download forms — StudyDownloadForm and ResourceDownloadForm now share a single DownloadForm base; both are now thin wrappers

server/auth.js

@@ -15,6 +15,7 @@ const totpPendingSessions = new Map()
 
 const ADMIN_SESSION_COOKIE = 'vbn_admin_session'
 const ADMIN_SESSION_TTL_MS = 7 * 24 * 60 * 60 * 1000
+const ADMIN_SESSION_ABSOLUTE_TTL_MS = 30 * 24 * 60 * 60 * 1000
 const ADMIN_PASSWORD = process.env.ADMIN_PASSWORD
 const adminSessions = new Map()
 
@@ -217,7 +218,8 @@ export function consumePendingSession(token) {
 
 export function createAdminSession() {
   const token = randomUUID()
-  adminSessions.set(token, Date.now() + ADMIN_SESSION_TTL_MS)
+  const now = Date.now()
+  adminSessions.set(token, { expiresAt: now + ADMIN_SESSION_TTL_MS, absoluteExpiresAt: now + ADMIN_SESSION_ABSOLUTE_TTL_MS })
   return token
 }
 
@@ -234,13 +236,20 @@ export function isValidAdminSession(req) {
   const sessionToken = cookies[ADMIN_SESSION_COOKIE]
   if (!sessionToken) return false
 
-  const expiresAt = adminSessions.get(sessionToken)
-  if (!expiresAt || expiresAt <= Date.now()) {
+  const now = Date.now()
+  const session = adminSessions.get(sessionToken)
+  if (!session) return false
+
+  // Support legacy sessions stored as a plain number (expiresAt)
+  const expiresAt = typeof session === 'object' ? session.expiresAt : session
+  const absoluteExpiresAt = typeof session === 'object' ? session.absoluteExpiresAt : Infinity
+
+  if (expiresAt <= now || absoluteExpiresAt <= now) {
     adminSessions.delete(sessionToken)
     return false
   }
 
-  adminSessions.set(sessionToken, Date.now() + ADMIN_SESSION_TTL_MS)
+  adminSessions.set(sessionToken, { expiresAt: now + ADMIN_SESSION_TTL_MS, absoluteExpiresAt })
   return true
 }
 

server/routes/contact.js

@@ -98,7 +98,7 @@ export function register(app) {
       if (lastName !== undefined && lastName !== null && (typeof lastName !== 'string' || lastName.trim().length > 100)) {
         res.status(400).json({ message: 'Last name is too long.' }); return
       }
-      if (!email || typeof email !== 'string' || !/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email.trim())) {
+      if (!email || typeof email !== 'string' || !/^[a-zA-Z0-9._%+\-]{1,64}@[a-zA-Z0-9.\-]{1,253}\.[a-zA-Z]{2,}$/.test(email.trim())) {
         res.status(400).json({ message: 'A valid email address is required.' }); return
       }
       if (!message || typeof message !== 'string' || message.trim().length < 5 || message.trim().length > 3000) {
@@ -470,7 +470,7 @@ export function register(app) {
       if (!submission) {
         res.status(404).json({ message: 'Submission not found.' }); return
       }
-      if (!submission.email || !/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(submission.email)) {
+      if (!submission.email || !/^[a-zA-Z0-9._%+\-]{1,64}@[a-zA-Z0-9.\-]{1,253}\.[a-zA-Z]{2,}$/.test(submission.email)) {
         res.status(400).json({ message: 'Submission does not have a valid email address.' }); return
       }
 

server/routes/downloads.js

@@ -67,7 +67,7 @@ export function register(app) {
       if (!lastName || typeof lastName !== 'string' || lastName.trim().length < 1 || lastName.trim().length > 100) {
         res.status(400).json({ message: 'Last name is required.' }); return
       }
-      if (!email || typeof email !== 'string' || !/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email.trim())) {
+      if (!email || typeof email !== 'string' || !/^[a-zA-Z0-9._%+\-]{1,64}@[a-zA-Z0-9.\-]{1,253}\.[a-zA-Z]{2,}$/.test(email.trim())) {
         res.status(400).json({ message: 'A valid email address is required.' }); return
       }
 
@@ -175,7 +175,7 @@ export function register(app) {
       if (!lastName || typeof lastName !== 'string' || lastName.trim().length < 1 || lastName.trim().length > 100) {
         res.status(400).json({ message: 'Last name is required.' }); return
       }
-      if (!email || typeof email !== 'string' || !/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email.trim())) {
+      if (!email || typeof email !== 'string' || !/^[a-zA-Z0-9._%+\-]{1,64}@[a-zA-Z0-9.\-]{1,253}\.[a-zA-Z]{2,}$/.test(email.trim())) {
         res.status(400).json({ message: 'A valid email address is required.' }); return
       }
 

server/routes/study-account.js

@@ -8,11 +8,15 @@ import { UPLOADS_DIR, EMAIL_CHANGE_TOKEN_TTL_MS } from '../config.js'
 import { state } from '../state.js'
 import {
   queueStudyUsersWrite,
+  queueStudyCommunityWrite,
+  queueStudyCommentsWrite,
+  queueStudyCertificatesWrite,
   readUploadsMetadata,
   writeUploadsMetadata,
   loadUserNotes,
   loadUserProgress,
   getUserNotesFilePath,
+  getUserProgressFilePath,
 } from '../data.js'
 import {
   requireStudyAuth,
@@ -259,6 +263,17 @@ export function register(app) {
         return
       }
 
+      const isValidImageBytes = (
+        (buffer[0] === 0xFF && buffer[1] === 0xD8 && buffer[2] === 0xFF) || // JPEG
+        (buffer[0] === 0x89 && buffer[1] === 0x50 && buffer[2] === 0x4E && buffer[3] === 0x47) || // PNG
+        (buffer[0] === 0x47 && buffer[1] === 0x49 && buffer[2] === 0x46) || // GIF
+        (buffer[0] === 0x52 && buffer[1] === 0x49 && buffer[2] === 0x46 && buffer[3] === 0x46) // WEBP (RIFF)
+      )
+      if (!isValidImageBytes) {
+        res.status(400).json({ message: 'Upload must be a valid PNG, JPG, WEBP, or GIF image.' })
+        return
+      }
+
       const baseName = normalizeAssetBaseName(filename.replace(/\.[a-z0-9]+$/i, ''))
       const finalName = `${baseName || 'avatar'}-${Date.now()}${ext}`
 
@@ -444,6 +459,21 @@ export function register(app) {
     state.studyNotesCache.delete(user.id)
     try { await unlink(getUserNotesFilePath(user.id)) } catch { /* no notes file is fine */ }
 
+    state.studyProgressCache.delete(user.id)
+    try { await unlink(getUserProgressFilePath(user.id)) } catch { /* no progress file is fine */ }
+
+    const beforeCerts = state.studyCertificates.length
+    state.studyCertificates = state.studyCertificates.filter(c => c.userId !== user.id)
+    if (state.studyCertificates.length !== beforeCerts) queueStudyCertificatesWrite()
+
+    const beforePosts = state.studyCommunityPosts.length
+    state.studyCommunityPosts = state.studyCommunityPosts.filter(p => p.authorUserId !== user.id)
+    if (state.studyCommunityPosts.length !== beforePosts) queueStudyCommunityWrite()
+
+    const beforeComments = state.studyComments.length
+    state.studyComments = state.studyComments.filter(c => c.userId !== user.id)
+    if (state.studyComments.length !== beforeComments) queueStudyCommentsWrite()
+
     sendStudyAccountDeletedEmail(deletedEmail, deletedDisplayName).catch(err => {
       console.error('[study-account] delete email error:', err)
     })

server/routes/study-certificate.js

@@ -1,9 +1,18 @@
 import { randomUUID } from 'node:crypto'
+import rateLimit from 'express-rate-limit'
 import { requireAdminAuth } from '../auth.js'
 import { requireStudyAuth, normalizeStudySlug, isStudyUserEnrolled, getStudyTitleBySlug } from '../study-helpers.js'
 import { state } from '../state.js'
 import { loadUserProgress, queueStudyCertificatesWrite } from '../data.js'
 
+const publicCertRateLimiter = rateLimit({
+  windowMs: 15 * 60 * 1000,
+  max: 30,
+  standardHeaders: true,
+  legacyHeaders: false,
+  message: { message: 'Too many certificate lookups. Please wait a moment.' },
+})
+
 /**
  * Returns the list of required section IDs for a study (only released sections).
  */
@@ -92,7 +101,7 @@ export function register(app) {
   })
 
   // GET — public certificate page data (no auth, by token)
-  app.get('/api/public/certificate/:token', (req, res) => {
+  app.get('/api/public/certificate/:token', publicCertRateLimiter, (req, res) => {
     const { token } = req.params
     if (!token || typeof token !== 'string' || token.length > 100) {
       res.status(400).json({ message: 'Invalid token.' }); return

server/routes/study-data.js

@@ -23,6 +23,19 @@ import {
 import { MAX_STUDY_NOTE_LENGTH, MAX_STUDY_NOTES_PER_USER, MAX_STUDY_ENROLLMENTS_PER_USER } from '../config.js'
 import { randomUUID } from 'node:crypto'
 
+const noteSaveHits = new Map() // userId -> { count, windowStart }
+const NOTE_RATE_WINDOW_MS = 60 * 1000
+const NOTE_RATE_MAX = 30
+
+function checkNoteSaveRateLimit(userId) {
+  const now = Date.now()
+  const entry = noteSaveHits.get(userId) ?? { count: 0, windowStart: now }
+  if (now - entry.windowStart > NOTE_RATE_WINDOW_MS) { entry.count = 0; entry.windowStart = now }
+  entry.count += 1
+  noteSaveHits.set(userId, entry)
+  return entry.count <= NOTE_RATE_MAX
+}
+
 export function register(app) {
   // ── Enrollment ────────────────────────────────────────────────────────────
 
@@ -112,6 +125,10 @@ export function register(app) {
       return
     }
     const user = req.studyUser
+    if (!checkNoteSaveRateLimit(user.id)) {
+      res.status(429).json({ message: 'Too many note saves. Please slow down.' })
+      return
+    }
     const noteStudySlug = getStudySlugFromNoteId(sectionId)
     if (noteStudySlug && !isStudyUserEnrolled(user, noteStudySlug)) {
       res.status(403).json({ message: 'Please enroll in this study to save notes.' })