Sign in with element x fails when using X25519MLKEM768

[LudoTren]

Steps to reproduce

After the last update to 26.02.0 i'm not able to log in to my homeserver, i get a server not found exception on ios while on android element x works fine. In the synapse logs the login request doesn't appear, element classic for ios works as usual

Outcome

What did you expect?

Log in successfully

What happened instead?

We were unable to reach this homeserver

Your phone model

iPhone 13

Operating system version

ios 26.2.1

Application version

element x: 26.02.0
synapse: version 1.147.0

Homeserver

synapse home server

Will you send logs?

Yes

[pixlwave]

Is this by any chance a coincidental occurrence of #786?

[LudoTren]

I don't think so , without encryption (via internal ip address,using HTTP only ) there is no issue. The server is not TLS1.3 only. In case it helps , I use nginx as reverse-proxy. No errors in the server logs file.

[pixlwave]

without encryption (via internal ip address,using HTTP only ) there is no issue.

Ok, well we're going to need some logs from the app to see what the errors are when you're attempting to access it from the external IP address/reverse-proxy please. If you reproduce the failure (noting the time) then it's probably easiest for you to login using the internal IP and then in the app's Settings choose Report A Problem, make sure the logs toggle is enabled and put the failure time along with a link to this issue in the comment box.

[LudoTren]

logs:
2026-02-18T22:30:30.441227Z DEBUG matrix_sdk::http_client: Error while sending request: Reqwest(reqwest::Error { kind: Request, url: "https://my-site-url/.well-known/matrix/client", source: hyper_util::client::legacy::Error(Connect, Error { code: -9824, message: "handshake unsuccessful" }) })

[pixlwave]

I'm not sure there's much more I can say other than -9824 is errSSLPeerHandshakeFail so there's something about your TLS setup that the Rust SDK doesn't like when used with native-tls support on iOS:

https://github.com/apple-oss-distributions/Security/blob/db15acbe6a7f257a859ad9a3bb86097bfe0679d9/base/SecBase.h#L833

It definitely sounds similar issue to #786 – which has a solution via matrix-org/matrix-rust-sdk#6053 to allow Rust to use the platform verifier for expanded TLS support.

[LudoTren]

Apparently the problem is that the new version of nginx uses X25519MLKEM768 post-quantum key exchange by default. And it's not supported by iOS. I fixed adding "ssl_conf_command Groups X25519:P-256:P-384;" to the end of http block