[jira] [Updated] (SSHD-1136) Diffie Hellmann group exchange falls back to insecure DHG1 if agreement on modulo size is not possible

["Achim Hügen (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SSHD-1136?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Achim Hügen updated SSHD-1136:
------------------------------
    Summary: Diffie Hellmann group exchange falls back to insecure DHG1 if agreement on modulo size is not possible  (was: Diffie Hellmann group exchange falls back to insecure DHG1 if agreement on moduli size is not possible)

> Diffie Hellmann group exchange falls back to insecure DHG1 if agreement on modulo size is not possible
> ------------------------------------------------------------------------------------------------------
>
>                 Key: SSHD-1136
>                 URL: https://issues.apache.org/jira/browse/SSHD-1136
>             Project: MINA SSHD
>          Issue Type: Bug
>    Affects Versions: 2.6.0
>            Reporter: Achim Hügen
>            Priority: Major
>
> After implementation of SSHD-1107 we configured the minimum modulo size of diffie-hellman-group-exchange-sha256 to 2048 bit and expected clients that doesn't support this minimum to not be able to connect.
> But what happens is that, those clients still can connect and this warning is logged:
> {code}
> chooseDH(DHGEXServer[diffie-hellman-group-exchange-sha256])[ShaftServerSession[null@/10.42.110.99:44222]][prf=1024, min=1024, max=1024] No suitable primes found, defaulting to DHG1
> {code}
> My understanding is, that this is a fallback to diffie-hellman-group1-sha1 which is week, see https://www.openssh.com/legacy.html
> Mina should make this fallback configurable and not activate it by default.



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