USN-4559-1: Samba update

30 September 2020

Several security improvements were added to Samba.

Releases

Packages

  • samba - SMB/CIFS file, print, and login server for Unix

Details

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.

Update instructions

The problem can be corrected by updating your system to the following package versions:

Ubuntu 20.04
Ubuntu 18.04
Ubuntu 16.04

In general, a standard system update will make all the necessary changes.

References

Related notices