Defend against configured known secret keys.

This is a two-prong effort. First, we warn on launch if a known key is
used. Second, we document using invalid keys where possible.

Co-authored-by: Jonas Møller <jonas@moesys.no>

core/lib/src/config/config.rs

@@ -364,6 +364,18 @@ impl Config {
         #[cfg(not(feature = "mtls"))] { false }
     }
 
+    #[cfg(feature = "secrets")]
+    pub(crate) fn known_secret_key_used(&self) -> bool {
+        const KNOWN_SECRET_KEYS: &'static [&'static str] = &[
+            "hPRYyVRiMyxpw5sBB1XeCMN1kFsDCqKvBi2QJxBVHQk="
+        ];
+
+        KNOWN_SECRET_KEYS.iter().any(|&key_str| {
+            let value = figment::value::Value::from(key_str);
+            self.secret_key == value.deserialize().expect("known key is valid")
+        })
+    }
+
     pub(crate) fn pretty_print(&self, figment: &Figment) {
         use crate::log::PaintExt;
 

core/lib/src/config/mod.rs

@@ -666,7 +666,7 @@ mod tests {
     fn test_no_err_on_release_and_custom_secret_key() {
         figment::Jail::expect_with(|jail| {
             jail.set_env("ROCKET_PROFILE", "release");
-            let key = "hPRYyVRiMyxpw5sBB1XeCMN1kFsDCqKvBi2QJxBVHQk=";
+            let key = "Bx4Gb+aSIfuoEyMHD4DvNs92+wmzfQK98qc6MiwyPY4=";
             let figment = Config::figment().merge(("secret_key", key));
 
             assert!(crate::local::blocking::Client::tracked(crate::custom(&figment)).is_ok());

core/lib/src/config/secret_key.rs

@@ -22,8 +22,13 @@ enum Kind {
 /// ```rust
 /// use rocket::config::Config;
 ///
+/// // NOTE: Don't (!) use this key! Generate your own and keep it private!
+/// //       e.g. via `head -c64 /dev/urandom | base64`
 /// let figment = Config::figment()
-///     .merge(("secret_key", "hPRYyVRiMyxpw5sBB1XeCMN1kFsDCqKvBi2QJxBVHQk="));
+///     # .merge(("secret_key", "hPRYyVRiMyxpw5sBB1XeCMN1kFsDCqKvBi2QJxBVHQk="));
+///     # /*
+///     .merge(("secret_key", "hPrYyЭRiMyµ5sBB1π+CMæ1køFsåqKvBiQJxBVHQk="));
+///     # */
 ///
 /// let config = Config::from(figment);
 /// assert!(!config.secret_key.is_zero());

core/lib/src/rocket.rs

@@ -530,7 +530,11 @@ impl Rocket<Build> {
                 config.secret_key = crate::config::SecretKey::generate()
                     .unwrap_or_else(crate::config::SecretKey::zero);
             }
-        };
+        } else if config.known_secret_key_used() {
+            warn!("The configured `secret_key` is exposed and insecure.");
+            warn_!("The configured key is publicly published and thus insecure.");
+            warn_!("Try generating a new key with `head -c64 /dev/urandom | base64`.");
+        }
 
         // Initialize the router; check for collisions.
         let mut router = Router::new();

examples/config/Rocket.toml

@@ -26,7 +26,8 @@ port = 8000
 workers = 12
 keep_alive = 5
 log_level = "critical"
-# don't use this key! generate your own and keep it private!
+# NOTE: Don't (!) use this key! Generate your own and keep it private!
+#       e.g. via `head -c64 /dev/urandom | base64`
 secret_key = "hPRYyVRiMyxpw5sBB1XeCMN1kFsDCqKvBi2QJxBVHQk="
 key = "a release app-key"
 extra = false

site/guide/9-configuration.md

@@ -126,11 +126,12 @@ limits = { json = "10MiB" }
 port = 9001
 
 ## set only when compiled in release mode, i.e, `cargo build --release`
-## don't use this secret_key! generate your own and keep it private!
 [release]
 port = 9999
-secret_key = "hPRYyVRiMyxpw5sBB1XeCMN1kFsDCqKvBi2QJxBVHQk="
 ip_header = false
+# NOTE: Don't (!) use this key! Generate your own and keep it private!
+#       e.g. via `head -c64 /dev/urandom | base64`
+secret_key = "hPrYyЭRiMyµ5sBB1π+CMæ1køFsåqKvBiQJxBVHQk="
 ```
 
 The following is a `Rocket.toml` file with all configuration options set for
@@ -150,8 +151,9 @@ ip_header = "X-Real-IP" # set to `false` to disable
 log_level = "normal"
 temp_dir = "/tmp"
 cli_colors = true
-## NOTE: Don't (!) use this key! Generate your own!
-secret_key = "hPRYyVRiMyxpw5sBB1XeCMN1kFsDCqKvBi2QJxBVHQk="
+# NOTE: Don't (!) use this key! Generate your own and keep it private!
+#       e.g. via `head -c64 /dev/urandom | base64`
+secret_key = "hPrYyЭRiMyµ5sBB1π+CMæ1køFsåqKvBiQJxBVHQk="
 
 [default.limits]
 form = "64 kB"