RFR: 8366244: TLS1.3 ChangeCipherSpec message received after the client's Finished message should trigger a connection abort with "unexpected message"

[Alice Pellegrini]

On Fri, 26 Sep 2025 15:38:20 GMT, Artur Barashev <abarashev at openjdk.org> wrote:

> According to the TLS specification, RFC 8446 section 5,
> 
> An implementation may receive an unencrypted record of type
>    change_cipher_spec consisting of the single byte value 0x01 at any
>    time after the first ClientHello message has been sent or received
>    and before the peer's Finished message has been received and MUST
>    simply drop it without further processing. Note that this record may
>    appear at a point at the handshake where the implementation is
>    expecting protected records, and so it is necessary to detect this
>    condition prior to attempting to deprotect the record. An
>    implementation which receives any other change_cipher_spec value or
>    which receives a protected change_cipher_spec record MUST abort the
>    handshake with an "unexpected_message" alert. If an implementation
>    detects a change_cipher_spec record received before the first
>    ClientHello message or after the peer's Finished message, it MUST be
>    treated as an unexpected record type (though stateless servers may
>    not be able to distinguish these cases from allowed cases).
> 
> 
> However the TLS implementation ignores a CCS message received after the client's Finished, instead of sending an alert(fatal, unexpected_message) and aborting the connection.

test/jdk/sun/security/ssl/SSLEngineImpl/TLS13ChangeCipherSpecAfterFinished.java line 122:

> 120:                 ex -> {
> 121:                     assertTrue(ex instanceof SSLProtocolException);
> 122:                     assertEquals(ex.getMessage(), exMsg);

nitpick: expected goes on the left hand side, [see here](https://github.com/openjdk/jdk/blob/fdbba049a2491c591fc1a866e4707bf9aac50f17/test/lib/jdk/test/lib/Asserts.java#L206-L210)

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PR Review Comment: https://git.openjdk.org/jdk/pull/27529#discussion_r2387985209