A Samba regression update has been released for Ubuntu Linux 20.04 LTS, 21.04, and 21.10.

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Ubuntu Security Notice USN-5142-2
December 06, 2021

samba regressions
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 21.10
- Ubuntu 21.04
- Ubuntu 20.04 LTS

Summary:

USN-5142-1 introduced regressions in Samba.

Software Description:
- samba: SMB/CIFS file, print, and login server for Unix

Details:

USN-5142-1 fixed vulnerabilities in Samba. Some of the upstream changes
introduced regressions in name mapping and backups.

Please see the following upstream bugs for more information:
  https://bugzilla.samba.org/show_bug.cgi?id=14901
  https://bugzilla.samba.org/show_bug.cgi?id=14918

This update fixes the problem.

Original advisory details:

Stefan Metzmacher discovered that Samba incorrectly handled SMB1 client
connections. A remote attacker could possibly use this issue to downgrade
connections to plaintext authentication. (CVE-2016-2124)
Andrew Bartlett discovered that Samba incorrectly mapping domain users to
local users. An authenticated attacker could possibly use this issue to
become root on domain members. (CVE-2020-25717)
Andrew Bartlett discovered that Samba did not correctly sandbox Kerberos
tickets issues by an RODC. An RODC could print administrator tickets,
contrary to expectations. (CVE-2020-25718)
Andrew Bartlett discovered that Samba incorrectly handled Kerberos tickets.
Delegated administrators could possibly use this issue to impersonate
accounts, leading to total domain compromise. (CVE-2020-25719)
Andrew Bartlett discovered that Samba did not provide stable AD
identifiers to Kerberos acceptors. (CVE-2020-25721)
Andrew Bartlett discovered that Samba did not properly check sensitive
attributes. An authenticated attacker could possibly use this issue to
escalate privileges. (CVE-2020-25722)
Stefan Metzmacher discovered that Samba incorrectly handled certain large
DCE/RPC requests. A remote attacker could possibly use this issue to
bypass signature requirements. (CVE-2021-23192)
William Ross discovered that Samba incorrectly handled memory. A remote
attacker could use this issue to cause Samba to crash, resulting in a
denial of service, or possibly escalate privileges. (CVE-2021-3738)
Joseph Sutton discovered that Samba incorrectly handled certain TGS
requests. An authenticated attacker could possibly use this issue to cause
Samba to crash, resulting in a denial of service. (CVE-2021-3671)
The fix for CVE-2020-25717 results in possible behaviour changes that could
affect certain environments. Please see the upstream advisory for more
information:
  https://www.samba.org/samba/security/CVE-2020-25717.html

Update instructions:

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

Ubuntu 21.10:
samba 2:4.13.14+dfsg-0ubuntu0.21.10.3

Ubuntu 21.04:
samba 2:4.13.14+dfsg-0ubuntu0.21.04.3

Ubuntu 20.04 LTS:
samba 2:4.13.14+dfsg-0ubuntu0.20.04.3

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

References:
  https://ubuntu.com/security/notices/USN-5142-2
  https://ubuntu.com/security/notices/USN-5142-1
  https://launchpad.net/bugs/1950363,   https://launchpad.net/bugs/1952187

Package Information:
  https://launchpad.net/ubuntu/+source/samba/2:4.13.14+dfsg-0ubuntu0.21.10.3
  https://launchpad.net/ubuntu/+source/samba/2:4.13.14+dfsg-0ubuntu0.21.04.3
  https://launchpad.net/ubuntu/+source/samba/2:4.13.14+dfsg-0ubuntu0.20.04.3