Formatting a client session value with Debug exposes its TLS 1.2 master secret or TLS 1.3 resumption PSK. A custom session store that logs these values can disclose keys to readers of the logs. Ordinary connection and built-in cache diagnostics remain redacted, and the session-store interface already warns that its values are sensitive.
In rustls 0.23.44 and 0.23.45, application data that a client buffers before the handshake completes is sent to the server even when the server rejects Encrypted Client Hello (ECH). When the server rejects ECH, the client completes the handshake with the outer ClientHello and authenticates the server against the ECH config's public_name. At the end of the handshake, start_traffic() encrypts and queues any plaintext buffered by ClientConnection::writer(). It does this …
The built-in (but disabled by default) Brotli certificate decoder bounds the output buffer but accepts an input-selected history window. A header of five bytes can specify a 1 GiB window allocation. A peer can abort a process whose allocator cannot satisfy that request. A client must enable Brotli and connect to the peer; a server must enable Brotli and request a client certificate. Neither direction requires a trusted attacker certificate.
The client records the server-selected key-exchange group per server name when it processes the ServerHello, before the server is authenticated. A network attacker can answer one connection attempt for a target name with a ServerHello that selects X25519 and close the connection. Later ClientHellos for that name carry one X25519 share while supported_groups still lists X25519MLKEM768 first. If the server accepts that share instead of sending a HelloRetryRequest, the handshake …
Rustls (tested version 0.23.44, and it appears still an issue on latest master though I have not tested this) accepts a TLS 1.3 server flight where a plaintext EncryptedExtensions is packed into the same record as the ServerHello. This is very similar to Go's CVE-2025-61730 fixed in https://github.com/golang/go/commit/5046bdf8a612b35a2c1a9e168054c1d5c65e7dd7
A bug introduced in rustls 0.23.13 leads to a panic if the received TLS ClientHello is fragmented. Only servers that use rustls::server::Acceptor::accept() are affected. Servers that use tokio-rustls's LazyConfigAcceptor API are affected. Servers that use tokio-rustls's TlsAcceptor API are not affected. Servers that use rustls-ffi's rustls_acceptor_accept API are affected.
rustls::ConnectionCommon::complete_io could fall into an infinite loop based on network input.