"Bad packet length 1231976033"

[Philip Prindeville]

I have a cron script that polls various machines for their configs and archives any changes.

When it connects to an OpenWrt router running "OpenSSH_9.1p1, OpenSSL 1.1.1s  1 Nov 2022", it sometimes gets this error:

Bad packet length 1231976033.
ssh_dispatch_run_fatal: Connection to 192.168.8.1 port 22: message authentication code incorrect

What's odd is that the length is *always* 1231976033 (which is 0x496E7661 or "Inva" in ASCII).

The client is Ubuntu 22.04.2 LTS, and it's version is "OpenSSH_9.1p1, OpenSSL 3.0.2 15 Mar 2022".

I googled this and there are various hypothesis like it's a mismatch in protocol negotiation versions (both client and server will only do Version 2); that my .bashrc file can't emit any output on the server (my server uses Ash); that there can't be an /etc/motd file; that I need to set 'LC_ALL="en_US.UTF-8"' when invoking ssh; and all sorts of other theories which seemed to be clutching at straws.

So, what's the real fix?

Thanks,

-Philip