Vulnerability RUSTSEC-2026-0285
Summary
TLS 1.3 handshake messages incorrectly accepted across encryption level boundaries
Details
Rustls accepted TLS 1.3 handshake messages sent at the wrong encryption level when they followed a key-changing message in the same record. For example, a plaintext EncryptedExtensions message packed into the same record as the ServerHello was accepted.
RFC 8446 section 5.1 requires that handshake messages do not span key changes, and that implementations terminate the connection with an "unexpected_message" alert if they do.
The handshake transcript is still authenticated, so a network-position attacker cannot use this to alter or complete a handshake; the practical effect is that a peer could send handshake messages that should be encrypted in plaintext without rustls rejecting the connection.
This is functionally the same bug as Go's GO-2026-4340 (CVE-2025-61730).
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