diff --git a/quantara/frontend/quantara.conf b/quantara/frontend/quantara.conf
index 71cc2c08..afc1134a 100644
--- a/quantara/frontend/quantara.conf
+++ b/quantara/frontend/quantara.conf
@@ -4,6 +4,11 @@ server {
 
     server_name localhost;
 
+    add_header X-Frame-Options "DENY" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+    add_header Content-Security-Policy "default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; font-src 'self'; connect-src 'self' https://*.stellar.org; frame-ancestors 'none';" always;
+
     location / {
         root   /usr/share/nginx/html;
         index  index.html;
diff --git a/quantara/frontend/quantara_dev.conf b/quantara/frontend/quantara_dev.conf
index 13a45951..5c19246e 100644
--- a/quantara/frontend/quantara_dev.conf
+++ b/quantara/frontend/quantara_dev.conf
@@ -18,6 +18,12 @@ server {
     ssl_session_cache shared:SSL:10m;
     ssl_session_timeout 10m;
 
+    add_header X-Frame-Options "DENY" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+    add_header Strict-Transport-Security "max-age=86400; includeSubDomains" always;
+    add_header Content-Security-Policy "default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; font-src 'self'; connect-src 'self' https://*.stellar.org; frame-ancestors 'none';" always;
+
     access_log /var/log/nginx/access.log;
     error_log /var/log/nginx/error.log;
 
diff --git a/quantara/web_app/api/main.py b/quantara/web_app/api/main.py
index 779b6646..3eb13441 100644
--- a/quantara/web_app/api/main.py
+++ b/quantara/web_app/api/main.py
@@ -33,7 +33,7 @@
 from web_app.api.wallet_auth import router as auth_router
 from web_app.api.metrics import router as metrics_router, PrometheusMiddleware
 from web_app.config_validator import assert_valid_config
-from web_app.api.middleware import MaxBodySizeMiddleware
+from web_app.api.middleware import MaxBodySizeMiddleware, SecurityHeadersMiddleware
 from web_app.db.database import init_db
 from web_app.db.database import init_db, get_database
 from web_app.utils.logger import configure_logging, get_logger
@@ -150,6 +150,7 @@ async def global_exception_handler(request: Request, exc: Exception):
 app.add_middleware(SlowAPIMiddleware)
 app.add_middleware(MaxBodySizeMiddleware, max_body_size=1024*1024)
 app.add_middleware(PrometheusMiddleware)
+app.add_middleware(SecurityHeadersMiddleware)
 
 
 @app.middleware("http")
diff --git a/quantara/web_app/api/middleware.py b/quantara/web_app/api/middleware.py
index 3bdde2ab..f7ce19af 100644
--- a/quantara/web_app/api/middleware.py
+++ b/quantara/web_app/api/middleware.py
@@ -1,4 +1,46 @@
 import json
+import os
+
+
+class SecurityHeadersMiddleware:
+    """ASGI middleware that injects security headers into every HTTP response.
+
+    Adds Content-Security-Policy, Strict-Transport-Security (production only),
+    X-Frame-Options, X-Content-Type-Options, and Referrer-Policy headers as a
+    defense-in-depth measure against XSS, clickjacking, MIME-sniffing, and
+    protocol-downgrade attacks.
+    """
+
+    def __init__(self, app):
+        self.app = app
+
+    async def __call__(self, scope, receive, send):
+        if scope["type"] != "http":
+            await self.app(scope, receive, send)
+            return
+
+        is_production = os.getenv("ENV_VERSION") == "PROD"
+
+        async def send_with_headers(message):
+            if message["type"] == "http.response.start":
+                headers = [
+                    (b"content-security-policy", b"default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; font-src 'self'; connect-src 'self' https://*.stellar.org; frame-ancestors 'none';"),
+                    (b"x-frame-options", b"DENY"),
+                    (b"x-content-type-options", b"nosniff"),
+                    (b"referrer-policy", b"strict-origin-when-cross-origin"),
+                ]
+                if is_production:
+                    headers.append((b"strict-transport-security", b"max-age=31536000; includeSubDomains"))
+
+                existing_headers = list(message.get("headers", []))
+                existing_names = {name.lower() for name, _ in existing_headers}
+                filtered = [h for h in existing_headers if h[0].lower() not in {name.lower() for name, _ in headers}]
+                message["headers"] = filtered + headers
+
+            await send(message)
+
+        await self.app(scope, receive, send_with_headers)
+
 
 class MaxBodySizeMiddleware:
     """ASGI middleware to enforce a maximum request body size.
diff --git a/quantara/web_app/tests/test_security_headers.py b/quantara/web_app/tests/test_security_headers.py
new file mode 100644
index 00000000..d47aa815
--- /dev/null
+++ b/quantara/web_app/tests/test_security_headers.py
@@ -0,0 +1,42 @@
+import pytest
+from httpx import AsyncClient
+from web_app.api.main import app
+from web_app.api.middleware import SecurityHeadersMiddleware
+
+
+def test_security_headers_registered():
+    middleware_classes = [m.cls for m in app.user_middleware]
+    assert SecurityHeadersMiddleware in middleware_classes
+
+
+@pytest.mark.asyncio
+async def test_security_headers_present():
+    async with AsyncClient(app=app, base_url="http://testserver") as client:
+        response = await client.get("/health")
+
+    assert response.headers.get("x-frame-options") == "DENY"
+    assert response.headers.get("x-content-type-options") == "nosniff"
+    assert response.headers.get("referrer-policy") == "strict-origin-when-cross-origin"
+    assert "content-security-policy" in response.headers
+    csp = response.headers["content-security-policy"]
+    assert "default-src 'self'" in csp
+    assert "frame-ancestors 'none'" in csp
+
+
+@pytest.mark.asyncio
+async def test_hsts_not_set_when_not_production(monkeypatch):
+    monkeypatch.setenv("ENV_VERSION", "DEV")
+    async with AsyncClient(app=app, base_url="http://testserver") as client:
+        response = await client.get("/health")
+    assert "strict-transport-security" not in response.headers
+
+
+@pytest.mark.asyncio
+async def test_hsts_set_in_production(monkeypatch):
+    monkeypatch.setenv("ENV_VERSION", "PROD")
+    async with AsyncClient(app=app, base_url="http://testserver") as client:
+        response = await client.get("/health")
+    assert "strict-transport-security" in response.headers
+    hsts = response.headers["strict-transport-security"]
+    assert "max-age=31536000" in hsts
+    assert "includeSubDomains" in hsts