Ubuntu Security Update USN-4559-1: Samba update


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Tom Tervoort discovered that the Netlogon protocol implemented by Samba incorrectly handled the authentication scheme. A remote attacker could use this issue to forge an authentication token and steal the credentials of the domain admin. While a previous security update fixed the issue by changing the "server schannel" setting to default to "yes", instead of "auto", which forced a secure netlogon channel, this update provides additional improvements. For compatibility reasons with older devices, Samba now allows specifying an insecure netlogon configuration per machine. See the following link for examples: https://www.samba.org/samba/security/CVE-2020-1472.html In addition, this update adds additional server checks for the protocol attack in the client-specified challenge to provide some protection when 'server schannel = no/auto' and avoid the false-positive results when running the proof-of-concept exploit.

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