Why does Wireshark show Version TLS 1.2 here instead of TLS 1.3

wireshark

I'm accessing TLS 1.3 test server "https://tls13.pinterjann.is" via a java http client using TLS 1.3. Everything seems to work fine as the html response indicates:

HTML Response

What I don't understand: Why does Wireshark show in the overview Protocol TLSv1.3 but in the details Version TLS 1.2?

Is Wireshark just displaying the wrong Version or am I actually using TLS 1.2?

Thanks in advance for your support.

Wireshark ClientHello
Wireshark HelloRetry
Wireshark ClientHello 2
Wireshark ServerHello

Best Answer

Sorry, for the confusion, I was missing the exact TLS 1.3 semantics: For instance, in the Client Hello, the field "version" must contain the fixed value 0x0303 (TLS 1.2), while the prefered version is contained in the extension "supported versions".

From RFC 8446 (TLS 1.3 spec): 

struct {
      ProtocolVersion legacy_version = 0x0303;    /* TLS v1.2 */
      Random random;
      opaque legacy_session_id<0..32>;
      CipherSuite cipher_suites<2..2^16-2>;
      opaque legacy_compression_methods<1..2^8-1>;
      Extension extensions<8..2^16-1>;
  } ClientHello;

legacy_version: In previous versions of TLS, this field was used for version negotiation and represented the highest version number supported by the client. Experience has shown that many servers do not properly implement version negotiation, leading to "version intolerance" in which the server rejects an otherwise acceptable ClientHello with a version number higher than it supports. In TLS 1.3, the client indicates its version preferences in the "supported_versions" extension (Section 4.2.1) and the legacy_version field MUST be set to 0x0303, which is the version number for TLS 1.2. TLS 1.3 ClientHellos are identified as having a legacy_version of 0x0303 and a supported_versions extension present with 0x0304 as the highest version indicated therein. (See Appendix D for details about backward compatibility.)

This agrees with what Wireshark displays:

Wireshark supported versions