fix(rumqttd): Implement constant-time password comparison in authenti…

…cation logic (#829)

rumqttd/CHANGELOG.md

@@ -28,7 +28,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Make write method return the number of bytes written correctly everywhere
 
 ### Security
-
+- Implement constant-time password comparison in authentication logic
 ---
 
 ## [rumqttd 0.19.0] - 12-12-2023

rumqttd/Cargo.toml

@@ -38,6 +38,7 @@ clap = { version = "4.4", features = ["derive"] }
 axum = "0.7.4"
 rand = "0.8.5"
 uuid = { version = "1.7.0", features = ["v4", "fast-rng"] }
+subtle = "2.5"
 
 [features]
 default = ["use-rustls", "websocket"]

rumqttd/src/link/remote.rs

@@ -12,6 +12,7 @@ use std::collections::VecDeque;
 use std::io;
 use std::sync::Arc;
 use std::time::Duration;
+use subtle::ConstantTimeEq;
 use tokio::time::error::Elapsed;
 use tokio::{select, time};
 use tracing::{trace, Span};
@@ -254,15 +255,13 @@ async fn handle_auth(
     }
 
     if let Some(pairs) = &config.auth {
-        let static_auth_verified = pairs
-            .iter()
-            .any(|(user, pass)| (user, pass) == (username, password));
-
-        if !static_auth_verified {
-            return Err(Error::InvalidAuth);
+        if let Some(stored_password) = pairs.get(username) {
+            if stored_password.as_bytes().ct_eq(password.as_bytes()).into() {
+                return Ok(());
+            }
         }
 
-        return Ok(());
+        return Err(Error::InvalidAuth);
     }
 
     Err(Error::InvalidAuth)