As per upstream advisory: Some DNS records (such as MX and NS records) usually contain data in the additional section. Samba's dnsserver RPC pipe (which is an administrative interface not used in the DNS server itself) made an error in handling the case where there are no records present: instead of noticing the lack of records, it dereferenced uninitialised memory, causing the RPC server to crash. This RPC server, which also serves protocols other than dnsserver, will be restarted after a short delay, but it is easy for an authenticated non-admin attacker to crash it again as soon as it returns. The Samba DNS server itself will continue to operate, but many RPC services will not.
Acknowledgments: Name: the Samba project Upstream: Francis Brosnan Blázquez (ASPL.es)
External References: https://www.samba.org/samba/security/CVE-2020-14383.html
Mitigation: The dnsserver task can be stopped by setting 'dcerpc endpoint servers = -dnsserver' in the smb.conf and restarting Samba.
Created samba tracking bugs for this issue: Affects: fedora-all [bug 1892640]
Upstream patches: samba-4.13.1: https://git.samba.org/?p=samba.git;a=commit;h=4cbf95e731b39b2dbfec02f33fd6b195d0b0f7a8 https://git.samba.org/?p=samba.git;a=commit;h=862d6fb6f3235126c96683516c12a284bcf84901 samba-4.12.9: https://git.samba.org/?p=samba.git;a=commit;h=2d7d1dff7d20d5b06ff50452e7f714af9f6a109e https://git.samba.org/?p=samba.git;a=commit;h=425c31a599bb96c7d01273fc50b682bc42dbed57 samba-4.11.15: https://git.samba.org/?p=samba.git;a=commit;h=2632e8ebae826a7305fe7d3948ee28b77d2ffbc0 https://git.samba.org/?p=samba.git;a=commit;h=8e09649351e9e8143b4bd0b76bcbd2cfb4d2f281
Statement: This issue does not affect the version of samba as shipped with Red Hat Enterprise Linux 6, 7, 8 and Red Hat Gluster Storage 3 as it does not include support for Active Directory Domain Controller.