ESB-2020.3417 – [Ubuntu] Samba: Increased privileges – Remote/unauthenticated

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             AUSCERT External Security Bulletin Redistribution

                               ESB-2020.3417
                         USN-4559-1: Samba update
                              1 October 2020

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Samba
Publisher:         Ubuntu
Operating System:  Ubuntu
Impact/Access:     Increased Privileges -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2020-1472  

Reference:         ESB-2020.3219
                   ESB-2020.3188

Original Bulletin: 
   https://usn.ubuntu.com/4559-1/

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USN-4559-1: Samba update
30 September 2020

Several security improvements were added to Samba.
Releases

  o Ubuntu 20.04 LTS
  o Ubuntu 18.04 LTS
  o Ubuntu 16.04 LTS

Packages

  o 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

  o samba - 2:4.11.6+dfsg-0ubuntu1.5

Ubuntu 18.04

  o samba - 2:4.7.6+dfsg~ubuntu-0ubuntu2.20

Ubuntu 16.04

  o samba - 2:4.3.11+dfsg-0ubuntu0.16.04.31

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

References

  o CVE-2020-1472

Related notices

  o USN-4510-1 : samba
  o USN-4510-2 : samba

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===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
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