diff --git a/src/core/api/dynamic-router.js b/src/core/api/dynamic-router.js
index eaef3c1..191bbf4 100644
--- a/src/core/api/dynamic-router.js
+++ b/src/core/api/dynamic-router.js
@@ -257,10 +257,16 @@ async function routeModuleRequest(request, path, method) {
             const params = extractPathParams(route.path, pathString);
             return await route.handler(request, params);
           }
-        } catch (authError) {
+        } catch (err) {
+          // Only known auth-error strings are safe to surface; all other
+          // exceptions are logged server-side and returned as a generic message.
+          const SAFE_AUTH_MESSAGES = new Set(['Unauthorized', 'Admin access required']);
+          if (!SAFE_AUTH_MESSAGES.has(err.message)) {
+            console.error('[ZEN] Module route handler error:', err);
+          }
           return {
             success: false,
-            error: authError.message
+            error: SAFE_AUTH_MESSAGES.has(err.message) ? err.message : 'Internal Server Error'
           };
         }
       }
diff --git a/src/core/api/handlers/users.js b/src/core/api/handlers/users.js
index 592a612..1b2eedf 100644
--- a/src/core/api/handlers/users.js
+++ b/src/core/api/handlers/users.js
@@ -8,7 +8,7 @@ import { cookies } from 'next/headers';
 import { query, updateById } from '@zen/core/database';
 import { getSessionCookieName } from '../../../shared/lib/appConfig.js';
 import { updateUser } from '../../../features/auth/lib/auth.js';
-import { uploadImage, deleteFile, generateUniqueFilename, generateUserFilePath, FILE_TYPE_PRESETS, FILE_SIZE_LIMITS, validateUpload } from '@zen/core/storage';
+import { uploadImage, deleteFile, generateUniqueFilename, generateUserFilePath, getFileExtension, FILE_TYPE_PRESETS, FILE_SIZE_LIMITS, validateUpload } from '@zen/core/storage';
 
 // Get cookie name from environment or use default
 const COOKIE_NAME = getSessionCookieName();
@@ -425,11 +425,17 @@ export async function handleUploadProfilePicture(request) {
     // Generate storage path
     const key = generateUserFilePath(session.user.id, 'profile', uniqueFilename);
 
-    // Derive the authoritative content-type from the server-side whitelist —
-    // never trust the client-supplied file.type, which is fully attacker-controlled.
-    const contentType = ALLOWED_IMAGE_MIME_TYPES.has(file.type)
-      ? file.type
-      : 'application/octet-stream';
+    // Derive the authoritative content-type from the *validated file extension*,
+    // never from file.type which is fully attacker-controlled.  The extension
+    // has already been verified against the allowedTypes whitelist above, so
+    // mapping it deterministically here eliminates any client influence over
+    // the MIME type stored in R2 and subsequently served to other users.
+    const EXTENSION_TO_MIME = {
+      '.jpg': 'image/jpeg', '.jpeg': 'image/jpeg',
+      '.png': 'image/png', '.gif': 'image/gif', '.webp': 'image/webp',
+    };
+    const ext = getFileExtension(file.name).toLowerCase();
+    const contentType = EXTENSION_TO_MIME[ext] ?? 'application/octet-stream';
 
     // Upload to storage
     const uploadResult = await uploadImage({
diff --git a/src/core/api/nx-route.js b/src/core/api/nx-route.js
index 276c1b1..4c39f21 100644
--- a/src/core/api/nx-route.js
+++ b/src/core/api/nx-route.js
@@ -19,18 +19,33 @@ export async function GET(request, { params }) {
     
     // Check if this is a file response (from storage endpoint)
     if (response.success && response.file) {
+      const contentType = response.file.contentType || 'application/octet-stream';
       const headers = {
-        'Content-Type': response.file.contentType || 'application/octet-stream',
+        'Content-Type': contentType,
         'Content-Length': response.file.contentLength?.toString() || '',
         'Cache-Control': 'private, max-age=3600',
         'Last-Modified': response.file.lastModified?.toUTCString() || new Date().toUTCString(),
         'X-Content-Type-Options': 'nosniff',
         'X-Frame-Options': 'DENY',
       };
-      if (response.file.filename) {
+
+      // Always emit an explicit Content-Disposition header — omitting it leaves
+      // rendering decisions to browser heuristics, which varies by content-type
+      // and browser version.  Image MIME types are served inline (required for
+      // <img> tags); every other type forces a download to prevent in-browser
+      // rendering of potentially dangerous content.
+      const INLINE_MIME_TYPES = new Set([
+        'image/jpeg', 'image/png', 'image/gif', 'image/webp',
+      ]);
+      if (INLINE_MIME_TYPES.has(contentType)) {
+        headers['Content-Disposition'] = 'inline';
+      } else if (response.file.filename) {
         const encoded = encodeURIComponent(response.file.filename);
         headers['Content-Disposition'] = `attachment; filename="${encoded}"; filename*=UTF-8''${encoded}`;
+      } else {
+        headers['Content-Disposition'] = 'attachment';
       }
+
       return new NextResponse(response.file.body, { status: 200, headers });
     }
     
diff --git a/src/core/api/router.js b/src/core/api/router.js
index 0509895..1b89e73 100644
--- a/src/core/api/router.js
+++ b/src/core/api/router.js
@@ -279,10 +279,18 @@ async function routeModuleRequest(request, path, method) {
           const params = extractPathParams(route.path, pathString);
           return await route.handler(request, params);
         }
-      } catch (authError) {
+      } catch (err) {
+        // Only the two known auth-error strings are safe to surface verbatim.
+        // Any other exception (database errors, upstream API errors, etc.) must
+        // never reach the client raw — they can contain credentials, table names,
+        // or internal hostnames. Log the full error server-side only.
+        const SAFE_AUTH_MESSAGES = new Set(['Unauthorized', 'Admin access required']);
+        if (!SAFE_AUTH_MESSAGES.has(err.message)) {
+          console.error('[ZEN] Module route handler error:', err);
+        }
         return {
           success: false,
-          error: authError.message
+          error: SAFE_AUTH_MESSAGES.has(err.message) ? err.message : 'Internal Server Error'
         };
       }
     }
diff --git a/src/core/storage/utils.js b/src/core/storage/utils.js
index 2221bc0..ec3196e 100644
--- a/src/core/storage/utils.js
+++ b/src/core/storage/utils.js
@@ -243,13 +243,56 @@ export const FILE_SIZE_LIMITS = {
   LARGE_FILE: 1024 * 1024 * 1024, // 1 GB
 };
 
+/**
+ * Known magic-byte sequences for each permitted image extension.
+ * Keyed by lower-case extension; value is the expected byte sequence at offset 0.
+ * WEBP requires a special compound check (RIFF....WEBP).
+ */
+const MAGIC_BYTES = {
+  '.jpg':  [0xFF, 0xD8, 0xFF],
+  '.jpeg': [0xFF, 0xD8, 0xFF],
+  '.png':  [0x89, 0x50, 0x4E, 0x47],
+  '.gif':  [0x47, 0x49, 0x46, 0x38],   // GIF87a or GIF89a
+};
+
+/**
+ * Confirm that the file buffer starts with the magic bytes expected for the
+ * file's declared extension.  This is a *positive* assertion — the file must
+ * prove it is the type it claims to be, not merely fail to match a denylist.
+ *
+ * A polyglot that prefixes a real image header before malicious payload still
+ * satisfies this check, so this function must always be used together with
+ * inspectBufferForDangerousContent which scans a larger region for script tags.
+ *
+ * @param {Buffer} buffer
+ * @param {string} filename
+ * @returns {boolean} true when the magic bytes match the declared extension
+ */
+export function validateMagicBytes(buffer, filename) {
+  if (!Buffer.isBuffer(buffer) || buffer.length < 12) return false;
+  const ext = getFileExtension(filename).toLowerCase();
+
+  // WebP: 'RIFF' at bytes 0-3, 'WEBP' at bytes 8-11
+  if (ext === '.webp') {
+    return buffer.slice(0, 4).toString('ascii') === 'RIFF'
+        && buffer.slice(8, 12).toString('ascii') === 'WEBP';
+  }
+
+  const expected = MAGIC_BYTES[ext];
+  if (!expected) return false;
+  return expected.every((byte, i) => buffer[i] === byte);
+}
+
 /**
  * Inspect the first bytes of a buffer for known-dangerous content signatures
  * that could indicate an HTML, SVG, or XML file disguised with an image extension.
  * This is a defence-in-depth layer — it does not replace server-side magic-byte
  * validation via a dedicated library (e.g. 'sharp' or 'file-type').
  *
- * @param {Buffer} buffer - First bytes of the uploaded file (minimum 16 bytes)
+ * The scan window is extended to 512 bytes to make it harder to hide a script
+ * tag after a short but valid-looking binary header.
+ *
+ * @param {Buffer} buffer - File buffer (ideally the full file, at least 512 bytes)
  * @returns {{ safe: boolean, reason: string|null }}
  */
 export function inspectBufferForDangerousContent(buffer) {
@@ -257,13 +300,15 @@ export function inspectBufferForDangerousContent(buffer) {
     return { safe: false, reason: 'Buffer too short to inspect' };
   }
 
-  // Convert the first 64 bytes to a lower-case ASCII string for pattern matching.
-  const head = buffer.slice(0, Math.min(buffer.length, 64)).toString('latin1').toLowerCase();
+  // Scan the first 512 bytes (up from 64) to reduce polyglot attack surface.
+  const head = buffer.slice(0, Math.min(buffer.length, 512)).toString('latin1').toLowerCase();
 
   // Detect HTML/SVG/XML content that could carry executable scripts.
   const dangerousPatterns = [
     /^<(!doctype|html|svg|xml|script)/,
     /^[\s\ufeff]*<(!doctype|html|svg|xml|script)/,
+    /<script[\s>]/,
+    /<svg[\s>]/,
   ];
 
   for (const pattern of dangerousPatterns) {
@@ -309,9 +354,17 @@ export function validateUpload({ filename, size, allowedTypes, maxSize, buffer }
     errors.push(`File size exceeds limit of ${formatFileSize(maxSize)}`);
   }
 
-  // If a buffer is provided, perform a best-effort content inspection to catch
-  // polyglot files (e.g., valid JPEG header with embedded SVG payload).
+  // If a buffer is provided, apply two independent layers of content inspection.
   if (buffer) {
+    // Layer 1 — Positive magic-byte assertion: the buffer must begin with the
+    // exact byte sequence that corresponds to the declared file extension.
+    // This catches files that lie about their extension entirely.
+    if (filename && !validateMagicBytes(buffer, filename)) {
+      errors.push('File magic bytes do not match the declared file type');
+    }
+
+    // Layer 2 — Dangerous-pattern denylist: scan a wider window for HTML/SVG/XML
+    // tags that could carry executable scripts (polyglot defence-in-depth).
     const inspection = inspectBufferForDangerousContent(buffer);
     if (!inspection.safe) {
       errors.push(inspection.reason || 'File content failed safety inspection');
diff --git a/src/features/auth/actions/authActions.js b/src/features/auth/actions/authActions.js
index c95cb16..2e772a2 100644
--- a/src/features/auth/actions/authActions.js
+++ b/src/features/auth/actions/authActions.js
@@ -103,14 +103,25 @@ export async function loginAction(formData) {
     const password = formData.get('password');
     
     const result = await login({ email, password });
-    
-    // Return the token to be set by the client to avoid page refresh
-    // The client will call setSessionCookie after displaying the success message
+
+    // Set the session cookie directly inside this server action so the token
+    // never travels through JavaScript-readable response payload.
+    // An HttpOnly cookie is the only safe transport for session tokens.
+    const cookieStore = await cookies();
+    cookieStore.set(COOKIE_NAME, result.session.token, {
+      httpOnly: true,
+      secure: process.env.NODE_ENV === 'production',
+      sameSite: 'lax',
+      maxAge: 60 * 60 * 24 * 30,
+      path: '/'
+    });
+
     return {
       success: true,
       message: 'Connexion réussie',
-      user: result.user,
-      sessionToken: result.session.token
+      user: result.user
+      // sessionToken intentionally omitted — it must never appear in a
+      // JavaScript-accessible response body.
     };
   } catch (error) {
     return {
diff --git a/src/features/auth/lib/auth.js b/src/features/auth/lib/auth.js
index eaeb5bf..768e5fd 100644
--- a/src/features/auth/lib/auth.js
+++ b/src/features/auth/lib/auth.js
@@ -6,7 +6,7 @@
 import { create, findOne, updateById, count } from '../../../core/database/crud.js';
 import { hashPassword, verifyPassword, generateId } from './password.js';
 import { createSession } from './session.js';
-import { createEmailVerification, createPasswordReset, deleteResetToken, sendPasswordChangedEmail } from './email.js';
+import { createEmailVerification, createPasswordReset, verifyResetToken, deleteResetToken, sendPasswordChangedEmail } from './email.js';
 
 /**
  * Register a new user
@@ -210,9 +210,14 @@ async function resetPassword(resetData) {
     throw new Error('Le mot de passe doit contenir au moins une majuscule, une minuscule et un chiffre');
   }
   
-  // Verify token is handled in the email module
-  // For now, we'll assume token is valid if it exists in the database
-  
+  // Authoritative token verification — this check must live here so that any
+  // caller that imports resetPassword() directly (bypassing the server-action
+  // layer) cannot reset a password with an arbitrary or omitted token.
+  const tokenValid = await verifyResetToken(email, token);
+  if (!tokenValid) {
+    throw new Error('Jeton de réinitialisation invalide ou expiré');
+  }
+
   // Find user
   const user = await findOne('zen_auth_users', { email });
   if (!user) {
diff --git a/src/features/auth/lib/email.js b/src/features/auth/lib/email.js
index cd5b56b..2382983 100644
--- a/src/features/auth/lib/email.js
+++ b/src/features/auth/lib/email.js
@@ -3,6 +3,7 @@
  * Handles email verification tokens and password reset tokens
  */
 
+import crypto from 'crypto';
 import { create, findOne, deleteWhere } from '../../../core/database/crud.js';
 import { generateToken, generateId } from './password.js';
 import { sendAuthEmail } from '../../../core/email/index.js';
@@ -55,19 +56,27 @@ async function verifyEmailToken(email, token) {
   });
   
   if (!verification) return false;
-  
-  // Verify token matches
-  if (verification.token !== token) return false;
-  
+
+  // Timing-safe comparison — always operate on same-length buffers so that a
+  // wrong-length guess yields no measurable timing difference from a wrong-value guess.
+  const storedBuf   = Buffer.from(verification.token, 'utf8');
+  const providedBuf = Buffer.from(
+    token.length === verification.token.length ? token : verification.token,
+    'utf8'
+  );
+  const tokensMatch = crypto.timingSafeEqual(storedBuf, providedBuf)
+                      && token.length === verification.token.length;
+  if (!tokensMatch) return false;
+
   // Check if token is expired
   if (new Date(verification.expires_at) < new Date()) {
     await deleteWhere('zen_auth_verifications', { id: verification.id });
     return false;
   }
-  
+
   // Delete the verification token after use
   await deleteWhere('zen_auth_verifications', { id: verification.id });
-  
+
   return true;
 }
 
@@ -118,16 +127,23 @@ async function verifyResetToken(email, token) {
   });
   
   if (!reset) return false;
-  
-  // Verify token matches
-  if (reset.token !== token) return false;
-  
+
+  // Timing-safe comparison — same rationale as verifyEmailToken above.
+  const storedBuf   = Buffer.from(reset.token, 'utf8');
+  const providedBuf = Buffer.from(
+    token.length === reset.token.length ? token : reset.token,
+    'utf8'
+  );
+  const tokensMatch = crypto.timingSafeEqual(storedBuf, providedBuf)
+                      && token.length === reset.token.length;
+  if (!tokensMatch) return false;
+
   // Check if token is expired
   if (new Date(reset.expires_at) < new Date()) {
     await deleteWhere('zen_auth_verifications', { id: reset.id });
     return false;
   }
-  
+
   return true;
 }
 
diff --git a/src/features/auth/lib/password.js b/src/features/auth/lib/password.js
index 0c0a434..36598bf 100644
--- a/src/features/auth/lib/password.js
+++ b/src/features/auth/lib/password.js
@@ -32,10 +32,18 @@ async function hashPassword(password) {
 async function verifyPassword(password, hash) {
   return new Promise((resolve, reject) => {
     const [salt, key] = hash.split(':');
-    
+
     crypto.scrypt(password, salt, 64, (err, derivedKey) => {
-      if (err) reject(err);
-      resolve(key === derivedKey.toString('hex'));
+      if (err) { reject(err); return; }
+      try {
+        const storedKey = Buffer.from(key, 'hex');
+        // timingSafeEqual requires identical lengths; if the stored hash is
+        // malformed the lengths will differ and we reject without leaking timing.
+        if (storedKey.length !== derivedKey.length) { resolve(false); return; }
+        resolve(crypto.timingSafeEqual(storedKey, derivedKey));
+      } catch {
+        resolve(false);
+      }
     });
   });
 }
diff --git a/src/features/auth/lib/rateLimit.js b/src/features/auth/lib/rateLimit.js
index 18a29c9..176591d 100644
--- a/src/features/auth/lib/rateLimit.js
+++ b/src/features/auth/lib/rateLimit.js
@@ -3,8 +3,16 @@
  * Stores counters in a Map — resets on server restart, no DB required.
  */
 
+// Persist the store on globalThis so that module-cache invalidation (e.g. during
+// Next.js hot reload) does not silently reset all counters within the same process.
+// CRITICAL LIMITATION: this Map is process-local. In serverless or multi-worker
+// deployments every instance maintains its own store and rate limits do not
+// distribute across instances. For production deployments with multiple workers
+// replace this Map with a shared atomic store (e.g. Redis / Upstash).
+const STORE_KEY = Symbol.for('__ZEN_RATE_LIMIT_STORE__');
+if (!globalThis[STORE_KEY]) globalThis[STORE_KEY] = new Map();
 /** @type {Map<string, { count: number, windowStart: number, windowMs: number, blockedUntil: number|null }>} */
-const store = new Map();
+const store = globalThis[STORE_KEY];
 
 // Purge expired entries every 10 minutes to avoid memory leak
 const cleanup = setInterval(() => {
@@ -76,29 +84,63 @@ export function checkRateLimit(identifier, action) {
 }
 
 /**
- * Extract the best-effort client IP from Next.js headers() (server actions).
+ * Return true only when the string resembles a valid IPv4 or IPv6 address.
+ * This prevents arbitrary attacker-supplied strings from being used as
+ * rate-limit identifiers (which could allow bucket manipulation).
+ * @param {string|null|undefined} ip
+ * @returns {boolean}
+ */
+function isValidIp(ip) {
+  if (!ip || typeof ip !== 'string') return false;
+  // IPv4 — four decimal octets, each 0-255
+  if (/^(\d{1,3}\.){3}\d{1,3}$/.test(ip)) {
+    return ip.split('.').every(octet => parseInt(octet, 10) <= 255);
+  }
+  // IPv6 — simplified structural check (colons + hex groups)
+  return /^[0-9a-fA-F:]+$/.test(ip) && ip.includes(':');
+}
+
+/**
+ * Extract the client IP from Next.js headers() (server actions).
+ *
+ * X-Forwarded-For and X-Real-IP are only trusted when ZEN_TRUST_PROXY=true is
+ * explicitly set, confirming a trusted reverse proxy populates those headers.
+ * Without this flag the headers are fully attacker-controlled and MUST NOT be
+ * used as rate-limit keys — an attacker would trivially rotate identifiers.
+ *
+ * Set ZEN_TRUST_PROXY=true only when a verified reverse proxy (e.g. Nginx,
+ * Cloudflare, AWS ALB) strips and rewrites forwarded headers before they reach
+ * this application.
+ *
  * @param {import('next/headers').ReadonlyHeaders} headersList
  * @returns {string}
  */
 export function getIpFromHeaders(headersList) {
-  return (
-    headersList.get('x-forwarded-for')?.split(',')[0]?.trim() ||
-    headersList.get('x-real-ip') ||
-    'unknown'
-  );
+  if (process.env.ZEN_TRUST_PROXY === 'true') {
+    const forwarded = headersList.get('x-forwarded-for')?.split(',')[0]?.trim();
+    if (forwarded && isValidIp(forwarded)) return forwarded;
+    const realIp = headersList.get('x-real-ip')?.trim();
+    if (realIp && isValidIp(realIp)) return realIp;
+  }
+  // Safe fallback — all requests share the 'unknown' bucket.
+  // Configure ZEN_TRUST_PROXY=true behind a verified reverse proxy.
+  return 'unknown';
 }
 
 /**
- * Extract the best-effort client IP from a Next.js Request object (API routes).
+ * Extract the client IP from a Next.js Request object (API routes).
+ * See getIpFromHeaders for the full trust-proxy rationale.
  * @param {Request} request
  * @returns {string}
  */
 export function getIpFromRequest(request) {
-  return (
-    request.headers.get('x-forwarded-for')?.split(',')[0]?.trim() ||
-    request.headers.get('x-real-ip') ||
-    'unknown'
-  );
+  if (process.env.ZEN_TRUST_PROXY === 'true') {
+    const forwarded = request.headers.get('x-forwarded-for')?.split(',')[0]?.trim();
+    if (forwarded && isValidIp(forwarded)) return forwarded;
+    const realIp = request.headers.get('x-real-ip')?.trim();
+    if (realIp && isValidIp(realIp)) return realIp;
+  }
+  return 'unknown';
 }
 
 /**