diff --git a/.github/workflows/security-pipeline.yml b/.github/workflows/security-pipeline.yml
index 6a0806e..5356f14 100644
--- a/.github/workflows/security-pipeline.yml
+++ b/.github/workflows/security-pipeline.yml
@@ -33,6 +33,7 @@ jobs:
         uses: gitleaks/gitleaks-action@b6c5701469c3e8b8f2ec5b3c81bda3f28b673af6 # v2.3.6
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITLEAKS_CONFIG: .gitleaks.toml
 
   sast:
     name: SAST – Static Analysis
diff --git a/.gitleaks.toml b/.gitleaks.toml
new file mode 100644
index 0000000..a3d5d01
--- /dev/null
+++ b/.gitleaks.toml
@@ -0,0 +1,23 @@
+[extend]
+# Extend gitleaks default rules
+useDefault = true
+
+[[rules]]
+id = "stellar-secret-key"
+description = "Stellar secret key (56-character key starting with S)"
+regex = '''(?i)(?:stellar|xlm|horizon)[^0-9A-Za-z]{0,30}S[A-Z2-7]{55}|S[A-Z2-7]{55}(?:[^0-9A-Za-z]|$)'''
+tags = ["stellar", "secret-key", "crypto"]
+keywords = ["stellar", "xlm", "secret"]
+
+[[rules]]
+id = "database-encryption-key"
+description = "DATABASE_ENCRYPTION_KEY value"
+regex = '''DATABASE_ENCRYPTION_KEY\s*=\s*[0-9a-fA-F]{64}'''
+tags = ["key", "database"]
+
+[allowlist]
+description = "Global allowlist for false positives"
+paths = [
+  ".gitleaksignore",
+  "CHANGELOG.md",
+]
diff --git a/.gitleaksignore b/.gitleaksignore
new file mode 100644
index 0000000..bb6751c
--- /dev/null
+++ b/.gitleaksignore
@@ -0,0 +1,8 @@
+# Suppress false positives from test fixtures that use intentionally fake keys.
+# Stellar testnet test vectors and clearly fake keys used only in unit tests.
+#
+# Format: <commit-hash>:<file-path>:<rule-id>
+# Use `gitleaks detect --verbose` to get the exact fingerprints to add here.
+#
+# Example (replace with real fingerprints after running gitleaks):
+# abc123:backend/tests/fixtures/stellar.js:stellar-secret-key
diff --git a/backend/prisma/schema.prisma b/backend/prisma/schema.prisma
index 8478788..0926338 100644
--- a/backend/prisma/schema.prisma
+++ b/backend/prisma/schema.prisma
@@ -304,3 +304,20 @@ model Session {
   @@index([userId])
   @@index([userId, revokedAt])
 }
+
+// Immutable audit trail for all admin actions (no UPDATE/DELETE should be issued against this table)
+model AdminAuditLog {
+  id               String   @id @default(uuid())
+  adminUserId      String
+  actionType       String
+  targetEntityType String
+  targetEntityId   String
+  actionMetadata   Json     @default("{}")
+  ipAddress        String?
+  userAgent        String?
+  createdAt        DateTime @default(now())
+
+  @@index([adminUserId])
+  @@index([actionType])
+  @@index([createdAt])
+}
diff --git a/backend/src/db/adminAuditLog.js b/backend/src/db/adminAuditLog.js
new file mode 100644
index 0000000..9c51e8b
--- /dev/null
+++ b/backend/src/db/adminAuditLog.js
@@ -0,0 +1,24 @@
+import prisma from './client.js';
+import logger from '../config/logger.js';
+
+/**
+ * Write an immutable audit log entry for an admin action.
+ * Failures are logged but never propagate — the action itself should not fail due to logging.
+ */
+export async function logAdminAction(adminId, actionType, targetType, targetId, metadata = {}, request = {}) {
+  try {
+    await prisma.adminAuditLog.create({
+      data: {
+        adminUserId: adminId,
+        actionType,
+        targetEntityType: targetType,
+        targetEntityId: targetId,
+        actionMetadata: metadata,
+        ipAddress: request.ip ?? null,
+        userAgent: request.get ? request.get('user-agent') ?? null : null,
+      },
+    });
+  } catch (err) {
+    logger.error({ err, adminId, actionType, targetType, targetId }, 'Failed to write admin audit log');
+  }
+}
diff --git a/backend/src/db/encryption.js b/backend/src/db/encryption.js
new file mode 100644
index 0000000..4b08636
--- /dev/null
+++ b/backend/src/db/encryption.js
@@ -0,0 +1,46 @@
+import { createCipheriv, createDecipheriv, randomBytes } from 'crypto';
+
+const ALGORITHM = 'aes-256-gcm';
+const IV_LENGTH = 12;
+
+function getKey() {
+  const raw = process.env.DATABASE_ENCRYPTION_KEY;
+  if (!raw) throw new Error('DATABASE_ENCRYPTION_KEY environment variable is required');
+  const key = Buffer.from(raw, 'hex');
+  if (key.length !== 32) throw new Error('DATABASE_ENCRYPTION_KEY must be 32 bytes (64 hex characters)');
+  return key;
+}
+
+/**
+ * Encrypt plaintext using AES-256-GCM.
+ * Returns a colon-separated string: iv:tag:ciphertext (all hex-encoded).
+ */
+export function encrypt(plaintext) {
+  const key = getKey();
+  const iv = randomBytes(IV_LENGTH);
+  const cipher = createCipheriv(ALGORITHM, key, iv);
+  const ciphertext = Buffer.concat([cipher.update(plaintext, 'utf8'), cipher.final()]);
+  const tag = cipher.getAuthTag();
+  return `${iv.toString('hex')}:${tag.toString('hex')}:${ciphertext.toString('hex')}`;
+}
+
+/**
+ * Decrypt a value produced by encrypt().
+ */
+export function decrypt(encryptedValue) {
+  const key = getKey();
+  const [ivHex, tagHex, ciphertextHex] = encryptedValue.split(':');
+  const iv = Buffer.from(ivHex, 'hex');
+  const tag = Buffer.from(tagHex, 'hex');
+  const ciphertext = Buffer.from(ciphertextHex, 'hex');
+  const decipher = createDecipheriv(ALGORITHM, key, iv);
+  decipher.setAuthTag(tag);
+  return Buffer.concat([decipher.update(ciphertext), decipher.final()]).toString('utf8');
+}
+
+/**
+ * Call at startup — fails fast with a clear error if the key is missing or invalid.
+ */
+export function validateEncryptionKey() {
+  getKey();
+}
diff --git a/backend/src/routes/admin.js b/backend/src/routes/admin.js
index ead2cc6..7f3969f 100644
--- a/backend/src/routes/admin.js
+++ b/backend/src/routes/admin.js
@@ -1,6 +1,7 @@
 import express from 'express';
 import prisma from '../db/client.js';
 import { requireAdmin } from '../middleware/adminAuth.js';
+import { logAdminAction } from '../db/adminAuditLog.js';
 
 const router = express.Router();
 
@@ -77,6 +78,7 @@ router.put('/kyc/:userId/approve', requireAdmin, async (req, res) => {
       where: { userId },
       data: { status: 'APPROVED', updatedAt: new Date() },
     });
+    logAdminAction(req.user.sub, 'KYC_APPROVE', 'USER', userId, {}, req);
     res.json({ success: true, kyc });
   } catch (error) {
     res.status(500).json({ error: 'Failed to approve KYC' });
@@ -90,10 +92,45 @@ router.put('/kyc/:userId/reject', requireAdmin, async (req, res) => {
       where: { userId },
       data: { status: 'REJECTED', updatedAt: new Date() },
     });
+    logAdminAction(req.user.sub, 'KYC_REJECT', 'USER', userId, {}, req);
     res.json({ success: true, kyc });
   } catch (error) {
     res.status(500).json({ error: 'Failed to reject KYC' });
   }
 });
 
+router.get('/audit-log', requireAdmin, async (req, res) => {
+  try {
+    const { page = 1, limit = 50, adminUserId, actionType, from, to } = req.query;
+    const take = Math.min(parseInt(limit), 200);
+    const skip = (parseInt(page) - 1) * take;
+
+    const where = {};
+    if (adminUserId) where.adminUserId = adminUserId;
+    if (actionType) where.actionType = actionType;
+    if (from || to) {
+      where.createdAt = {};
+      if (from) where.createdAt.gte = new Date(from);
+      if (to) where.createdAt.lte = new Date(to);
+    }
+
+    const [logs, total] = await Promise.all([
+      prisma.adminAuditLog.findMany({
+        where,
+        skip,
+        take,
+        orderBy: { createdAt: 'desc' },
+      }),
+      prisma.adminAuditLog.count({ where }),
+    ]);
+
+    res.json({
+      logs,
+      pagination: { page: parseInt(page), limit: take, total, pages: Math.ceil(total / take) },
+    });
+  } catch (error) {
+    res.status(500).json({ error: 'Failed to retrieve audit log' });
+  }
+});
+
 export default router;
\ No newline at end of file
diff --git a/backend/src/routes/webhooks.js b/backend/src/routes/webhooks.js
index 8fdf0eb..ddbcd66 100644
--- a/backend/src/routes/webhooks.js
+++ b/backend/src/routes/webhooks.js
@@ -1,6 +1,7 @@
 import express from 'express';
 import { requireAuth } from '../middleware/auth.js';
 import { registerWebhook, listWebhooks, deleteWebhook, rotateWebhookSecret, verifyWebhookSignature } from '../webhooks/store.js';
+import { webhookSignatureMiddleware } from '../webhooks/verifySignature.js';
 import logger from '../config/logger.js';
 
 const router = express.Router();
@@ -174,6 +175,17 @@ router.post('/:id/rotate-secret', requireAuth, (req, res) => {
  *       200:
  *         description: Verification result
  */
+/**
+ * POST /api/v1/webhooks/incoming
+ * Receive and process incoming webhook payloads from external services.
+ * Signature is verified via HMAC-SHA256 before any processing occurs.
+ */
+router.post('/incoming', webhookSignatureMiddleware, (req, res) => {
+  logger.info({ source: req.headers['x-webhook-source'] ?? 'unknown' }, 'Incoming webhook received');
+  // Dispatch to application logic based on payload type
+  res.status(200).json({ received: true });
+});
+
 router.post('/verify', (req, res) => {
   const { webhookId, signature, payload } = req.body;
   
diff --git a/backend/src/server.js b/backend/src/server.js
index 6c5674b..74e27a8 100644
--- a/backend/src/server.js
+++ b/backend/src/server.js
@@ -58,9 +58,18 @@ import { sanitizeInputs } from './middleware/sanitize.js';
 import { startScheduler, stopScheduler } from './scheduler.js';
 import { csrfTokenMiddleware, validateCSRFMiddleware, csrfTokenEndpoint } from './middleware/csrf.js';
 import dotenv from 'dotenv';
+import { validateEncryptionKey } from './db/encryption.js';
 
 dotenv.config();
 
+// Fail fast if the database encryption key is missing or invalid
+try {
+  validateEncryptionKey();
+} catch (err) {
+  console.error(`[startup] ${err.message}`);
+  process.exit(1);
+}
+
 const app = express();
 const PORT = getConfig().server.port;
 
diff --git a/backend/src/webhooks/store.js b/backend/src/webhooks/store.js
index 6d55b31..a8afd73 100644
--- a/backend/src/webhooks/store.js
+++ b/backend/src/webhooks/store.js
@@ -1,4 +1,4 @@
-import { createHmac, randomBytes } from 'crypto';
+import { createHmac, randomBytes, timingSafeEqual } from 'crypto';
 import logger from '../config/logger.js';
 
 // In-memory webhook store (replace with DB in production)
@@ -60,14 +60,22 @@ export function verifyWebhookSignature(webhookId, signature, payload) {
   const webhook = getWebhook(webhookId);
   if (!webhook) return false;
 
+  const safeEqual = (a, b) => {
+    try {
+      return timingSafeEqual(Buffer.from(a, 'hex'), Buffer.from(b, 'hex'));
+    } catch {
+      return false;
+    }
+  };
+
   // Try current secret
   const expectedSignature = signPayload(webhook.signingSecret, payload);
-  if (signature === expectedSignature) return true;
+  if (safeEqual(signature, expectedSignature)) return true;
 
   // Try previous secrets (for rotation grace period)
   for (const oldSecret of webhook.previousSecrets) {
     const oldSignature = signPayload(oldSecret, payload);
-    if (signature === oldSignature) return true;
+    if (safeEqual(signature, oldSignature)) return true;
   }
 
   return false;
diff --git a/backend/src/webhooks/verifySignature.js b/backend/src/webhooks/verifySignature.js
new file mode 100644
index 0000000..6236df5
--- /dev/null
+++ b/backend/src/webhooks/verifySignature.js
@@ -0,0 +1,44 @@
+import { createHmac, timingSafeEqual } from 'crypto';
+import logger from '../config/logger.js';
+
+/**
+ * Verify an HMAC-SHA256 signature from an incoming webhook request.
+ * Uses timingSafeEqual to prevent timing attacks.
+ *
+ * @param {Buffer} rawBody - Raw request body buffer (before JSON parsing)
+ * @param {string} signature - Signature from the request header (hex string)
+ * @param {string} secret - The shared signing secret
+ * @returns {boolean}
+ */
+export function verifyHmacSignature(rawBody, signature, secret) {
+  if (!signature || !secret) return false;
+  const expected = createHmac('sha256', secret).update(rawBody).digest('hex');
+  try {
+    return timingSafeEqual(Buffer.from(signature, 'hex'), Buffer.from(expected, 'hex'));
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Express middleware that verifies incoming webhook signatures.
+ * Reads the secret from WEBHOOK_SIGNING_SECRET env variable.
+ * Returns 401 on failure without revealing why.
+ */
+export function webhookSignatureMiddleware(req, res, next) {
+  const secret = process.env.WEBHOOK_SIGNING_SECRET;
+  if (!secret) {
+    logger.warn('WEBHOOK_SIGNING_SECRET not set — skipping signature verification');
+    return next();
+  }
+
+  const signature = req.headers['x-webhook-signature'] ?? req.headers['x-hub-signature-256'];
+  const rawBody = req.rawBody ?? Buffer.from(JSON.stringify(req.body));
+
+  if (!verifyHmacSignature(rawBody, signature, secret)) {
+    logger.warn({ ip: req.ip, path: req.path }, 'Invalid webhook signature rejected');
+    return res.status(401).json({ error: 'Unauthorized' });
+  }
+
+  next();
+}