diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 1a9528255..f783e97c7 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -17,3 +17,8 @@
 **Vulnerability:** The `verify_github_sig` function in `apps/server/src/infra_routes.rs` verified GitHub webhook signatures using standard string comparison `expected.eq_ignore_ascii_case(hex_sig)`.
 **Learning:** String comparison functions exit early as soon as a character mismatch is found. In a cryptographic context, this variable response time leaks information and allows an attacker to perform a timing attack to forge a valid HMAC signature by guessing it byte by byte.
 **Prevention:** Always use a constant-time comparison library (like `hmac`'s `verify_slice()`) to compare cryptographic hashes, secrets, and signatures to prevent side-channel timing attacks. Avoid custom implementations of standard cryptographic algorithms.
+
+## 2024-05-18 - [Missing Security Headers]
+**Vulnerability:** Missing important security headers like `X-Frame-Options`, `X-Content-Type-Options`, `Strict-Transport-Security`.
+**Learning:** Axum doesn't add security headers by default. Tower has some utilities, but we can also use custom middleware.
+**Prevention:** Implement standard security headers for all HTTP responses in `apps/server/src/security.rs`.
diff --git a/apps/server/src/main.rs b/apps/server/src/main.rs
index e4e00e95c..80068bdf3 100644
--- a/apps/server/src/main.rs
+++ b/apps/server/src/main.rs
@@ -469,6 +469,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
             state.clone(),
             worker::fence_stale_leader,
         ))
+        .layer(middleware::from_fn(security::security_headers))
         .layer(middleware::from_fn(security::static_cache_headers))
         .layer(security::cors_layer())
         .layer(TraceLayer::new_for_http())
diff --git a/apps/server/src/security.rs b/apps/server/src/security.rs
index 8ea417ea1..5be3f72f4 100644
--- a/apps/server/src/security.rs
+++ b/apps/server/src/security.rs
@@ -2,7 +2,7 @@
 
 use axum::{
     body::Body,
-    http::{header, HeaderValue, Method, Request, Response},
+    http::{header, HeaderName, HeaderValue, Method, Request, Response},
     middleware::Next,
 };
 use tower_http::cors::{AllowOrigin, CorsLayer};
@@ -51,6 +51,31 @@ pub fn cors_layer() -> CorsLayer {
 
 /// HTML / routes app : pas de cache (évite page blanche après MAJ Flatpak).
 /// Assets fingerprinted `/_astro/*` : cache long.
+/// Ajoute des en-têtes de sécurité standard à toutes les réponses HTTP.
+pub async fn security_headers(req: Request<Body>, next: Next) -> Response<Body> {
+    let mut res = next.run(req).await;
+    let headers = res.headers_mut();
+
+    headers.insert(
+        HeaderName::from_static("x-content-type-options"),
+        HeaderValue::from_static("nosniff"),
+    );
+    headers.insert(
+        HeaderName::from_static("x-frame-options"),
+        HeaderValue::from_static("sameorigin"),
+    );
+    headers.insert(
+        HeaderName::from_static("strict-transport-security"),
+        HeaderValue::from_static("max-age=31536000; includeSubDomains"),
+    );
+    headers.insert(
+        HeaderName::from_static("x-xss-protection"),
+        HeaderValue::from_static("1; mode=block"),
+    );
+
+    res
+}
+
 pub async fn static_cache_headers(req: Request<Body>, next: Next) -> Response<Body> {
     let path = req.uri().path().to_string();
     let mut res = next.run(req).await;