Add TLS handshake timeout (review #010 C3)

tls_handshake_timeout_secs (default 10s, must be > 0) wraps
tls_acceptor.accept() in tokio::time::timeout so stalled handshakes
(slowloris / crawler slow-handshake vector) can no longer hold an FD +
semaphore permit indefinitely. Config plumbing through FullConfig /
StaticConfig / validation / reload diff + docs.

README.md

@@ -116,6 +116,7 @@ Configuration uses TOML and is split into **static** (requires restart) and
 | `admin_key_path` | `/etc/reverse-proxy/admin-key` | Path to admin Bearer token file (empty string to disable) |
 | `shutdown_timeout_secs` | `30` | Graceful shutdown timeout |
 | `connection_idle_timeout_secs` | `60` | Server-side idle timeout for client TLS connections (prevents FD exhaustion from abandoned connections) |
+| `tls_handshake_timeout_secs` | `10` | Max seconds to complete the TLS handshake; stalled handshakes are closed (prevents slowloris FD/permit exhaustion) |
 | `max_connections` | `1024` | Max concurrent client TLS connections (backpressure via semaphore) |
 | `logging.level` | `"info"` | Log level |
 | `logging.format` | `"text"` | Log format (`"text"` or `"json"`) |

docs/architecture/config.md

@@ -91,6 +91,7 @@ Immutable after startup. Changes require a process restart.
 | `admin_key_path` | `String` | Path to file containing the admin Bearer token (default: `/etc/reverse-proxy/admin-key`; empty string to disable admin endpoints; see ADR-028) |
 | `shutdown_timeout_secs` | `u64` | Maximum seconds to wait for in-flight requests during graceful shutdown (default: `30`) |
 | `connection_idle_timeout_secs` | `u64` | Server-side idle timeout for client TLS connections. Idle HTTP/2 connections are closed after this duration (with keep-alive pings at 15s intervals to detect dead peers). HTTP/1.1 connections are closed if the client doesn't send a complete request header within this duration. Prevents FD exhaustion from abandoned connections (default: `60`; must be > 0; see review #007 C1) |
+| `tls_handshake_timeout_secs` | `u64` | Maximum seconds a client may take to complete the TLS handshake. Stalled handshakes (e.g. crawlers/slowloris clients that open a TCP connection but never send a ClientHello) are closed after this duration, releasing the FD and connection slot. Without it, a stalled handshake holds an FD + connection semaphore permit indefinitely (default: `10`; must be > 0; see review #010 C3) |
 | `max_connections` | `usize` | Maximum number of concurrent client TLS connections. When the limit is reached, new connections wait in the OS TCP backlog until a slot frees (default: `1024`; must be > 0; see review #007 C2) |
 | `logging` | `LoggingConfig` | Logging configuration (see below) |
 
@@ -185,6 +186,7 @@ Phase 2.
 | `admin_key_path` | `String` | `/etc/reverse-proxy/admin-key` | No |
 | `shutdown_timeout_secs` | `u64` | `30` | No |
 | `connection_idle_timeout_secs` | `u64` | `60` | No |
+| `tls_handshake_timeout_secs` | `u64` | `10` | No |
 | `max_connections` | `usize` | `1024` | No |
 | `logging.level` | `String` | `"info"` | No |
 | `logging.format` | `String` | `"text"` | No |
@@ -313,6 +315,7 @@ certificate:
 health_check_port = 9900     # Local health check (0 to disable)
 admin_key_path = "/etc/reverse-proxy/admin-key"  # Empty string to disable
 # connection_idle_timeout_secs = 60  # Server-side idle timeout (default: 60)
+# tls_handshake_timeout_secs = 10     # TLS handshake timeout (default: 10)
 # max_connections = 1024              # Max concurrent TLS connections (default: 1024)
 
 [logging]
@@ -461,6 +464,9 @@ On startup, the config is validated:
      review #007 C1.
 22. `max_connections` must be > 0. A zero value would deadlock the connection
      semaphore, preventing any client connection from being accepted.
+23. `tls_handshake_timeout_secs` must be > 0. A zero value would immediately
+     kill every TLS handshake, preventing any client connection from
+     completing (review #010 C3).
 
 On SIGHUP reload, the same validation applies. If the new config fails
 validation, the reload is rejected and the old config remains active. An error

docs/reviews/010-emfile-accept-loop-flood.md

@@ -20,8 +20,9 @@ fixes:
     C1: FIXED 2026-09-13 — accept-loop error classification + backoff +
     signature-keyed log de-duplication (src/server.rs).
   - >-
-    C3: OPEN — next priority. No TLS handshake timeout; stalled handshakes
-    hold an FD + a semaphore permit indefinitely (src/server.rs:370).
+    C3: FIXED 2026-09-13 — TLS handshake timeout (tls_handshake_timeout_secs,
+    default 10s) wraps tls_acceptor.accept() in src/server.rs; stalled
+    handshakes release FD + permit.
   - >-
     C4: OPEN — connection semaphore is per-listener (src/server.rs:338), so
     the effective cap is max_connections × listeners; sequence before C2 so
@@ -177,14 +178,16 @@ Notes from implementation:
   accept errors (axum 0.8.9 `src/serve/listener.rs` →
   `handle_accept_error`). No change needed there; the busy-spin existed
   only in the custom HTTPS loop.
-- Two follow-up findings surfaced while fixing C1 (still open, tracked
-  in "Recommended next steps"):
-  - **C3 (new)**: `tls_acceptor.accept()` has no timeout — a stalled TLS
-    handshake holds an FD *and* a semaphore permit indefinitely (the idle
-    watchdog only starts after the handshake completes). This is the
-    likely actual FD-exhaustion vector for slow/held crawler
+- Two follow-up findings surfaced while fixing C1 (tracked in
+  "Recommended next steps"):
+  - ~~**C3 (new)**~~ — **FIXED 2026-09-13**: `tls_acceptor.accept()` had
+    no timeout, so a stalled TLS handshake held an FD *and* a semaphore
+    permit indefinitely (the idle watchdog only starts after the
+    handshake completes). Fixed via `tls_handshake_timeout_secs`
+    (default 10s) wrapping the accept in `tokio::time::timeout`. This
+    was the likely actual FD-exhaustion vector for slow/held crawler
     handshakes, and a slowloris amplifier.
-  - **C4 (new)**: `conn_sem` is per-listener (`main.rs` spawns one
+  - **C4 (open)**: `conn_sem` is per-listener (`main.rs` spawns one
     `serve_https_listener` per listener, each creating its own
     semaphore), so the effective connection cap is
     `max_connections × listeners`. Any C2 RLIMIT cross-check must
@@ -262,7 +265,7 @@ observed limit).
 
 Residual risk after mitigation: none identified for FD exhaustion at
 current traffic (peak concurrent connections observed ≪ 800); the code
-findings C3/C4/C2 remain the durable fix (C1 landed 2026-09-13).
+findings C4/C2 remain the durable fix (C1 + C3 landed 2026-09-13).
 
 ## Traffic-analysis side note (from the same investigation)
 
@@ -288,13 +291,13 @@ behavior, which is exactly what made the EMFILE state reachable.
 
 1. ~~Land C1 (accept-loop error backoff + log de-duplication)~~ — DONE
    2026-09-13 (see Finding C1).
-2. Land C3 (TLS handshake timeout) — bound stalled handshakes so they
-   cannot hold FD + permit indefinitely; directly closes the crawler
-   slow-handshake vector described under "Trigger conditions". **Next
-   priority**: it is the likely actual trigger of the incident (stalled
-   crawler handshakes under the pre-mitigation 1024 cap), it is the only
-   finding that defends against a live attacker (slowloris amplifier),
-   and it does not interact with C2/C4 design decisions.
+2. ~~Land C3 (TLS handshake timeout)~~ — DONE 2026-09-13. New static config
+   `tls_handshake_timeout_secs` (default 10s, must be > 0) wraps
+   `tls_acceptor.accept()` in `tokio::time::timeout`
+   (`accept_tls_with_timeout()`, src/server.rs). On timeout the handshake
+   future is dropped, releasing the TCP FD and the semaphore permit; the
+   idle watchdog never needs to run for a stalled handshake. Closes the
+   crawler slow-handshake vector described under "Trigger conditions".
 3. Land C4 (shared connection semaphore across listeners) so
    `max_connections` is a global cap rather than per-listener. Sequenced
    before C2 because the RLIMIT cross-check's FD budget depends on the

src/config/dynamic_config.rs

@@ -189,6 +189,9 @@ fn diff_static_config(old: &StaticConfig, new: &StaticConfig) -> Vec<String> {
     if old.connection_idle_timeout_secs != new.connection_idle_timeout_secs {
         changes.push("connection_idle_timeout_secs".to_string());
     }
+    if old.tls_handshake_timeout_secs != new.tls_handshake_timeout_secs {
+        changes.push("tls_handshake_timeout_secs".to_string());
+    }
     if old.max_connections != new.max_connections {
         changes.push("max_connections".to_string());
     }

src/config/mod.rs

@@ -51,6 +51,8 @@ pub struct FullConfig {
     pub shutdown_timeout_secs: u64,
     #[serde(default = "static_config::default_connection_idle_timeout_secs")]
     pub connection_idle_timeout_secs: u64,
+    #[serde(default = "static_config::default_tls_handshake_timeout_secs")]
+    pub tls_handshake_timeout_secs: u64,
     #[serde(default = "static_config::default_max_connections")]
     pub max_connections: usize,
     #[serde(default)]
@@ -72,6 +74,7 @@ impl FullConfig {
             admin_key_path: self.admin_key_path,
             shutdown_timeout_secs: self.shutdown_timeout_secs,
             connection_idle_timeout_secs: self.connection_idle_timeout_secs,
+            tls_handshake_timeout_secs: self.tls_handshake_timeout_secs,
             max_connections: self.max_connections,
             logging: self.logging,
         };

src/config/static_config.rs

@@ -13,6 +13,8 @@ pub struct StaticConfig {
     pub shutdown_timeout_secs: u64,
     #[serde(default = "default_connection_idle_timeout_secs")]
     pub connection_idle_timeout_secs: u64,
+    #[serde(default = "default_tls_handshake_timeout_secs")]
+    pub tls_handshake_timeout_secs: u64,
     #[serde(default = "default_max_connections")]
     pub max_connections: usize,
     #[serde(default)]
@@ -35,6 +37,10 @@ pub fn default_connection_idle_timeout_secs() -> u64 {
     60
 }
 
+pub fn default_tls_handshake_timeout_secs() -> u64 {
+    10
+}
+
 pub fn default_max_connections() -> usize {
     1024
 }
@@ -213,6 +219,8 @@ upstream = "127.0.0.1:8080"
         shutdown_timeout_secs: u64,
         #[serde(default = "default_connection_idle_timeout_secs")]
         connection_idle_timeout_secs: u64,
+        #[serde(default = "default_tls_handshake_timeout_secs")]
+        tls_handshake_timeout_secs: u64,
         #[serde(default = "default_max_connections")]
         max_connections: usize,
         #[serde(default)]
@@ -232,6 +240,7 @@ upstream = "127.0.0.1:8080"
         assert_eq!(config.admin_key_path, "/etc/reverse-proxy/admin-key");
         assert_eq!(config.shutdown_timeout_secs, 30);
         assert_eq!(config.connection_idle_timeout_secs, 60);
+        assert_eq!(config.tls_handshake_timeout_secs, 10);
         assert_eq!(config.max_connections, 1024);
         assert_eq!(config.logging.level, "info");
         assert_eq!(config.logging.format, "text");
@@ -315,6 +324,8 @@ acme_cache_dir = "/tmp/cache"
             shutdown_timeout_secs: u64,
             #[serde(default = "default_connection_idle_timeout_secs")]
             connection_idle_timeout_secs: u64,
+            #[serde(default = "default_tls_handshake_timeout_secs")]
+            tls_handshake_timeout_secs: u64,
             #[serde(default = "default_max_connections")]
             max_connections: usize,
             #[serde(default)]
@@ -330,6 +341,7 @@ acme_cache_dir = "/tmp/cache"
         assert_eq!(config.admin_key_path, "/etc/reverse-proxy/admin-key");
         assert_eq!(config.shutdown_timeout_secs, 30);
         assert_eq!(config.connection_idle_timeout_secs, 60);
+        assert_eq!(config.tls_handshake_timeout_secs, 10);
         assert_eq!(config.max_connections, 1024);
         assert_eq!(config.logging.level, "info");
         assert_eq!(config.logging.format, "text");

src/config/test_fixtures.rs

@@ -23,6 +23,7 @@ pub fn test_static_config() -> StaticConfig {
         admin_key_path: "/etc/reverse-proxy/admin-key".to_string(),
         shutdown_timeout_secs: 30,
         connection_idle_timeout_secs: 60,
+        tls_handshake_timeout_secs: 10,
         max_connections: 1024,
         logging: LoggingConfig::default(),
     }

src/config/validation.rs

@@ -79,6 +79,8 @@ pub enum ValidationError {
     AdminKeyPathTraversal { path: String },
     #[error("connection_idle_timeout_secs must be > 0, got {value}")]
     ConnectionIdleTimeoutZero { value: u64 },
+    #[error("tls_handshake_timeout_secs must be > 0, got {value}")]
+    TlsHandshakeTimeoutZero { value: u64 },
     #[error("max_connections must be > 0, got {value}")]
     MaxConnectionsZero { value: usize },
 }
@@ -292,6 +294,12 @@ pub fn validate(
         });
     }
 
+    if static_config.tls_handshake_timeout_secs == 0 {
+        errors.push(ValidationError::TlsHandshakeTimeoutZero {
+            value: static_config.tls_handshake_timeout_secs,
+        });
+    }
+
     if static_config.max_connections == 0 {
         errors.push(ValidationError::MaxConnectionsZero {
             value: static_config.max_connections,
@@ -393,6 +401,7 @@ mod tests {
             admin_key_path: "/etc/reverse-proxy/admin-key".to_string(),
             shutdown_timeout_secs: 30,
             connection_idle_timeout_secs: 60,
+            tls_handshake_timeout_secs: 10,
             max_connections: 1024,
             logging: LoggingConfig::default(),
         }
@@ -431,6 +440,7 @@ mod tests {
             admin_key_path: "/etc/reverse-proxy/admin-key".to_string(),
             shutdown_timeout_secs: 30,
             connection_idle_timeout_secs: 60,
+            tls_handshake_timeout_secs: 10,
             max_connections: 1024,
             logging: LoggingConfig::default(),
         }
@@ -1121,6 +1131,7 @@ mod tests {
             admin_key_path: "/etc/reverse-proxy/admin-key".to_string(),
             shutdown_timeout_secs: 30,
             connection_idle_timeout_secs: 60,
+            tls_handshake_timeout_secs: 10,
             max_connections: 1024,
             logging: LoggingConfig::default(),
         };
@@ -1340,6 +1351,19 @@ mod tests {
             .any(|e| matches!(e, ValidationError::ConnectionIdleTimeoutZero { value: 0 })));
     }
 
+    #[test]
+    fn rule_tls_handshake_timeout_zero_rejected() {
+        let mut config = valid_static_config();
+        config.tls_handshake_timeout_secs = 0;
+        let dynamic = valid_dynamic_config();
+        let result = validate(&config, &dynamic, false);
+        assert!(result.is_err());
+        let errors = result.unwrap_err();
+        assert!(errors
+            .iter()
+            .any(|e| matches!(e, ValidationError::TlsHandshakeTimeoutZero { value: 0 })));
+    }
+
     #[test]
     fn rule_max_connections_zero_rejected() {
         let mut config = valid_static_config();

src/main.rs

@@ -234,6 +234,9 @@ async fn run_server(loaded_config: cli::LoadedConfig, config_path: &str) -> Resu
             std::time::Duration::from_secs(
                 loaded_config.static_config.connection_idle_timeout_secs,
             ),
+            std::time::Duration::from_secs(
+                loaded_config.static_config.tls_handshake_timeout_secs,
+            ),
             loaded_config.static_config.max_connections,
         ));
 

src/server.rs

@@ -108,6 +108,26 @@ async fn handle_accept_error(reporter: &AcceptErrorReporter, e: std::io::Error)
     }
 }
 
+pub const DEFAULT_TLS_HANDSHAKE_TIMEOUT_SECS: u64 = 10;
+
+async fn accept_tls_with_timeout(
+    tls_acceptor: TlsAcceptor,
+    tcp_stream: tokio::net::TcpStream,
+    timeout: Duration,
+) -> Result<tokio_rustls::server::TlsStream<tokio::net::TcpStream>, AcceptTlsError> {
+    match tokio::time::timeout(timeout, tls_acceptor.accept(tcp_stream)).await {
+        Ok(Ok(stream)) => Ok(stream),
+        Ok(Err(e)) => Err(AcceptTlsError::Handshake(e)),
+        Err(_) => Err(AcceptTlsError::Timeout),
+    }
+}
+
+#[derive(Debug)]
+pub enum AcceptTlsError {
+    Handshake(std::io::Error),
+    Timeout,
+}
+
 pub struct InFlightCounter {
     count: AtomicUsize,
 }
@@ -325,6 +345,7 @@ async fn idle_watchdog(idle_state: Arc<IdleState>, timeout: Duration) {
     }
 }
 
+#[allow(clippy::too_many_arguments)]
 pub async fn serve_https_listener(
     tcp_listener: TcpListener,
     tls_acceptor: TlsAcceptor,
@@ -332,6 +353,7 @@ pub async fn serve_https_listener(
     mut shutdown_rx: tokio::sync::watch::Receiver<bool>,
     in_flight: Arc<InFlightCounter>,
     connection_idle_timeout: Duration,
+    tls_handshake_timeout: Duration,
     max_connections: usize,
 ) {
     let local_addr = tcp_listener.local_addr();
@@ -367,14 +389,30 @@ pub async fn serve_https_listener(
                     let _guard = InFlightGuard::new(in_flight.clone());
                     let _permit = permit;
 
-                    let tls_stream = match tls_acceptor.accept(tcp_stream).await {
+                    let tls_result = match accept_tls_with_timeout(
+                        tls_acceptor,
+                        tcp_stream,
+                        tls_handshake_timeout,
+                    )
+                    .await
+                    {
                         Ok(stream) => stream,
-                        Err(e) => {
+                        Err(AcceptTlsError::Timeout) => {
+                            warn!(
+                                remote_addr = %remote_addr,
+                                timeout_secs = tls_handshake_timeout.as_secs(),
+                                "TLS handshake timeout; closing stalled handshake"
+                            );
+                            return;
+                        }
+                        Err(AcceptTlsError::Handshake(e)) => {
                             warn!(error = %e, "TLS handshake failed");
                             return;
                         }
                     };
 
+                    let tls_stream = tls_result;
+
                     let alpn = tls_stream.get_ref().1.alpn_protocol();
                     let is_h2 = alpn == Some(b"h2");
 
@@ -590,6 +628,142 @@ mod tests {
         assert_eq!(reports.len(), 2);
     }
 
+    #[tokio::test(start_paused = true)]
+    async fn accept_tls_with_timeout_times_out_on_stalled_handshake() {
+        use tokio::io::AsyncReadExt;
+        use tokio::net::TcpListener;
+
+        let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
+        let addr = listener.local_addr().unwrap();
+
+        let client = tokio::spawn(async move {
+            let stream = tokio::net::TcpStream::connect(addr).await.unwrap();
+            let mut stream = stream;
+            let mut buf = [0u8; 16];
+            let _ = stream.read(&mut buf).await;
+        });
+
+        let (tcp_stream, _remote_addr) = listener.accept().await.unwrap();
+        let tls_acceptor = test_tls_acceptor();
+
+        let start = tokio::time::Instant::now();
+        let result =
+            accept_tls_with_timeout(tls_acceptor, tcp_stream, Duration::from_secs(3)).await;
+        client.abort();
+
+        assert!(matches!(result, Err(AcceptTlsError::Timeout)));
+        assert_eq!(start.elapsed(), Duration::from_secs(3));
+    }
+
+    #[tokio::test]
+    async fn accept_tls_with_timeout_completes_real_handshake() {
+        use tokio::net::TcpListener;
+        use tokio_rustls::TlsConnector;
+
+        let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
+        let addr = listener.local_addr().unwrap();
+
+        let client_config = test_client_tls_config();
+        let connector = TlsConnector::from(client_config);
+        let server_name =
+            rustls::pki_types::ServerName::try_from("test.local".to_string()).unwrap();
+
+        let client = tokio::spawn(async move {
+            let stream = tokio::net::TcpStream::connect(addr).await.unwrap();
+            connector.connect(server_name, stream).await
+        });
+
+        let (tcp_stream, _remote_addr) = listener.accept().await.unwrap();
+        let tls_acceptor = test_tls_acceptor();
+
+        let result = accept_tls_with_timeout(
+            tls_acceptor,
+            tcp_stream,
+            Duration::from_secs(5),
+        )
+        .await;
+
+        assert!(result.is_ok(), "real handshake should complete: {result:?}");
+        client.abort();
+    }
+
+    fn test_tls_acceptor() -> TlsAcceptor {
+        use rustls::pki_types::{PrivateKeyDer, PrivatePkcs8KeyDer};
+
+        let mut params = rcgen::CertificateParams::new(vec!["test.local".to_string()]).unwrap();
+        params.distinguished_name = rcgen::DistinguishedName::new();
+        params
+            .distinguished_name
+            .push(rcgen::DnType::CommonName, "test.local");
+        let key_pair = rcgen::KeyPair::generate().unwrap();
+        let cert = params.self_signed(&key_pair).unwrap();
+        let cert_der = cert.der().clone();
+        let key_der = key_pair.serialize_der();
+        let private_key = PrivateKeyDer::Pkcs8(PrivatePkcs8KeyDer::from(key_der));
+
+        let config = rustls::ServerConfig::builder()
+            .with_no_client_auth()
+            .with_single_cert(vec![cert_der], private_key)
+            .unwrap();
+        TlsAcceptor::from(std::sync::Arc::new(config))
+    }
+
+    fn test_client_tls_config() -> std::sync::Arc<rustls::ClientConfig> {
+        let config = rustls::ClientConfig::builder()
+            .dangerous()
+            .with_custom_certificate_verifier(std::sync::Arc::new(UnverifiedCert))
+            .with_no_client_auth();
+        std::sync::Arc::new(config)
+    }
+
+    #[derive(Debug)]
+    struct UnverifiedCert;
+
+    impl rustls::client::danger::ServerCertVerifier for UnverifiedCert {
+        fn verify_server_cert(
+            &self,
+            _end_entity: &rustls::pki_types::CertificateDer<'_>,
+            _intermediates: &[rustls::pki_types::CertificateDer<'_>],
+            _server_name: &rustls::pki_types::ServerName<'_>,
+            _ocsp_response: &[u8],
+            _now: rustls::pki_types::UnixTime,
+        ) -> Result<rustls::client::danger::ServerCertVerified, rustls::Error> {
+            Ok(rustls::client::danger::ServerCertVerified::assertion())
+        }
+
+        fn verify_tls12_signature(
+            &self,
+            _message: &[u8],
+            _cert: &rustls::pki_types::CertificateDer<'_>,
+            _dss: &rustls::DigitallySignedStruct,
+        ) -> Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error> {
+            Ok(rustls::client::danger::HandshakeSignatureValid::assertion())
+        }
+
+        fn verify_tls13_signature(
+            &self,
+            _message: &[u8],
+            _cert: &rustls::pki_types::CertificateDer<'_>,
+            _dss: &rustls::DigitallySignedStruct,
+        ) -> Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error> {
+            Ok(rustls::client::danger::HandshakeSignatureValid::assertion())
+        }
+
+        fn supported_verify_schemes(&self) -> Vec<rustls::SignatureScheme> {
+            vec![
+                rustls::SignatureScheme::RSA_PKCS1_SHA256,
+                rustls::SignatureScheme::ECDSA_NISTP256_SHA256,
+                rustls::SignatureScheme::RSA_PSS_SHA256,
+                rustls::SignatureScheme::RSA_PKCS1_SHA384,
+                rustls::SignatureScheme::ECDSA_NISTP384_SHA384,
+                rustls::SignatureScheme::RSA_PSS_SHA384,
+                rustls::SignatureScheme::RSA_PKCS1_SHA512,
+                rustls::SignatureScheme::RSA_PSS_SHA512,
+                rustls::SignatureScheme::ED25519,
+            ]
+        }
+    }
+
     #[tokio::test(start_paused = true)]
     async fn handle_accept_error_sleeps_on_resource_errors() {
         let reporter = AcceptErrorReporter::new();

tests/integration_test.rs

@@ -1163,6 +1163,19 @@ mod idle_timeout_tests {
         Arc<InFlightCounter>,
         tokio::task::JoinHandle<()>,
         tokio::sync::watch::Sender<bool>,
+    ) {
+        start_test_https_server_with_timeouts(idle_timeout, Duration::from_secs(10), upstream).await
+    }
+
+    async fn start_test_https_server_with_timeouts(
+        idle_timeout: Duration,
+        handshake_timeout: Duration,
+        upstream: String,
+    ) -> (
+        std::net::SocketAddr,
+        Arc<InFlightCounter>,
+        tokio::task::JoinHandle<()>,
+        tokio::sync::watch::Sender<bool>,
     ) {
         let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
         let addr = listener.local_addr().unwrap();
@@ -1181,6 +1194,7 @@ mod idle_timeout_tests {
                 shutdown_rx,
                 in_flight_clone,
                 idle_timeout,
+                handshake_timeout,
                 1024,
             )
             .await;
@@ -1436,4 +1450,93 @@ mod idle_timeout_tests {
 
         let _ = upstream.shutdown_tx.send(());
     }
+
+    // Reproducer for review #010 C3: a client that opens a TCP connection but
+    // never sends a TLS ClientHello must not hold its FD + semaphore permit
+    // indefinitely. The server must close the stalled handshake after
+    // tls_handshake_timeout and release the permit.
+    #[tokio::test]
+    async fn stalled_tls_handshake_closed_after_timeout_and_permit_released() {
+        let handshake_timeout = Duration::from_millis(300);
+        let upstream = helpers::http_test_helper::TestUpstream::spawn_ok().await;
+        let upstream_addr = format!("127.0.0.1:{}", upstream.addr.port());
+        let (addr, in_flight, _handle, _shutdown_tx) =
+            start_test_https_server_with_timeouts(
+                Duration::from_secs(60),
+                handshake_timeout,
+                upstream_addr,
+            )
+            .await;
+
+        let stalled = tokio::net::TcpStream::connect(addr).await.unwrap();
+        // Hold the connection open without sending anything (stalled handshake).
+
+        // Wait past the handshake timeout.
+        tokio::time::sleep(handshake_timeout + Duration::from_millis(500)).await;
+
+        // The server must have dropped the stalled connection: reading from it
+        // should yield EOF (or an error), not hang.
+        let mut stalled = stalled;
+        let mut buf = [0u8; 16];
+        let read_result =
+            tokio::time::timeout(Duration::from_secs(2), stalled.read(&mut buf)).await;
+        let closed = match read_result {
+            Err(_) => panic!("stalled handshake was not closed by the server"),
+            Ok(Ok(0)) => true,
+            Ok(Ok(_)) => false,
+            Ok(Err(e)) if e.kind() == std::io::ErrorKind::UnexpectedEof => true,
+            Ok(Err(_)) => true,
+        };
+        assert!(
+            closed,
+            "server should close stalled TLS handshake after timeout"
+        );
+
+        // The semaphore permit and in-flight guard must have been released.
+        tokio::time::sleep(Duration::from_millis(100)).await;
+        assert_eq!(
+            in_flight.count(),
+            0,
+            "in-flight count should return to 0 after stalled handshake closed"
+        );
+
+        let _ = upstream.shutdown_tx.send(());
+    }
+
+    // A real TLS handshake must complete comfortably within the timeout —
+    // the timeout must only kill stalled handshakes, not legitimate clients.
+    #[tokio::test]
+    async fn real_handshake_completes_within_handshake_timeout() {
+        let handshake_timeout = Duration::from_millis(300);
+        let upstream = helpers::http_test_helper::TestUpstream::spawn_ok().await;
+        let upstream_addr = format!("127.0.0.1:{}", upstream.addr.port());
+        let (addr, in_flight, _handle, _shutdown_tx) =
+            start_test_https_server_with_timeouts(
+                Duration::from_secs(60),
+                handshake_timeout,
+                upstream_addr,
+            )
+            .await;
+
+        let mut tls_stream = connect_tls(addr).await;
+
+        tls_stream
+            .write_all(b"GET / HTTP/1.1\r\nHost: test.local\r\nConnection: keep-alive\r\n\r\n")
+            .await
+            .unwrap();
+
+        let mut buf = vec![0u8; 4096];
+        let n = tokio::time::timeout(Duration::from_secs(2), tls_stream.read(&mut buf))
+            .await
+            .expect("timeout waiting for response")
+            .expect("read error");
+        let response = String::from_utf8_lossy(&buf[..n]);
+        assert!(
+            response.starts_with("HTTP/1.1 200 OK"),
+            "expected a real 200 round-trip, got: {response}"
+        );
+        assert_eq!(in_flight.count(), 1, "connection should remain in-flight");
+
+        let _ = upstream.shutdown_tx.send(());
+    }
 }