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Enhance TLS record handling and security tests

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- Enforce TLS record length constraints in client handling to comply with RFC 8446, rejecting records outside the range of 512 to 16,384 bytes.
- Update security tests to validate behavior for oversized and undersized TLS records, ensuring they are correctly masked or rejected.
- Introduce new tests to verify the handling of TLS records in both generic and client handler pipelines.
- Refactor handshake logic to enforce mode restrictions based on transport type, preventing misuse of secure tags.
- Add tests for nonce generation and encryption consistency, ensuring correct behavior for different configurations.
- Improve masking tests to ensure proper logging and detection of client types, including SSH and unknown probes.
This commit is contained in:
David Osipov
2026-03-16 20:43:49 +04:00
parent 6ffbc51fb0
commit 5a16e68487
5 changed files with 1060 additions and 21 deletions
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41
src/proxy/handshake.rs
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@@ -21,6 +21,28 @@ use crate::tls_front::{TlsFrontCache, emulator};
const ACCESS_SECRET_BYTES: usize = 16;
// Decide whether a client-supplied proto tag is allowed given the configured
// proxy modes and the transport that carried the handshake.
//
// A common mistake is to treat `modes.tls` and `modes.secure` as interchangeable
// even though they correspond to different transport profiles: `modes.tls` is
// for the TLS-fronted (EE-TLS) path, while `modes.secure` is for direct MTProto
// over TCP (DD). Enforcing this separation prevents an attacker from using a
// TLS-capable client to bypass the operator intent for the direct MTProto mode,
// and vice versa.
fn mode_enabled_for_proto(config: &ProxyConfig, proto_tag: ProtoTag, is_tls: bool) -> bool {
match proto_tag {
ProtoTag::Secure => {
if is_tls {
config.general.modes.tls
} else {
config.general.modes.secure
}
}
ProtoTag::Intermediate | ProtoTag::Abridged => config.general.modes.classic,
}
}
fn decode_user_secrets(
config: &ProxyConfig,
preferred_user: Option<&str>,
@@ -292,16 +314,7 @@ where
None => continue,
};
let mode_ok = match proto_tag {
ProtoTag::Secure => {
if is_tls {
config.general.modes.tls || config.general.modes.secure
} else {
config.general.modes.secure || config.general.modes.tls
}
}
ProtoTag::Intermediate | ProtoTag::Abridged => config.general.modes.classic,
};
let mode_ok = mode_enabled_for_proto(config, proto_tag, is_tls);
if !mode_ok {
debug!(peer = %peer, user = %user, proto = ?proto_tag, "Mode not enabled");
@@ -324,8 +337,12 @@ where
let encryptor = AesCtr::new(&enc_key, enc_iv);
// Apply replay tracking only after successful authentication to prevent
// unauthenticated probes from evicting legitimate replay-cache entries.
// Apply replay tracking only after successful authentication.
//
// This ordering prevents an attacker from producing invalid handshakes that
// still collide with a valid handshake's replay slot and thus evict a valid
// entry from the cache. We accept the cost of performing the full
// authentication check first to avoid poisoning the replay cache.
if replay_checker.check_and_add_handshake(dec_prekey_iv) {
warn!(peer = %peer, user = %user, "MTProto replay attack detected");
return HandshakeResult::BadClient { reader, writer };