Interacting with Git remotes on codefloe via SSH I am seeing these warnings when I pull, push or clone:
** WARNING: connection is not using a post-quantum key exchange algorithm.
** This session may be vulnerable to "store now, decrypt later" attacks.
** The server may need to be upgraded. See https://openssh.com/pq.html
For reference, on my system ssh -V yields OpenSSH_10.2p1, OpenSSL 3.6.1 27 Jan 2026.
Presumably, this is due to an older version of OpenSSH running on the server. This should likely be upgraded, shouldn’t it?
This happens with recent OpenSSH versions (10+) when connecting to an older OpenSSH version on the server. It is not as scary as it may sound though but surely good
CodeFloe currently runs on a AlmaLinux 9 hosts which ships 8.7p1 as of right now. Only versions 9+ use either sntrup761x25519-sha512 or mlkem768x25519-sha256 by default. We just checked and it seems that 8.7p1 also supports sntrup761x25519-sha512 but it needs to be preferred manually over the others. The negotiated algorithm depends on an interplay of the client (advertising a specific algorithm) and the server returning all available ones. Depending on preferences on either side and the eventual chosen algorithm, the warning is issued or not.
We now altered the algorithm preference order on these hosts. sntrup761x25519-sha512@openssh.com should now be advertised when you connect to CodeFloe:
ssh -vv -T git@codefloe.com 2>&1 | grep "kex: algo"
debug1: kex: algorithm: sntrup761x25519-sha512@openssh.com
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