Preface: Samba is an implementation of the Server Message Block (SMB)/Common Internet File System (CIFS) protocol for Unix systems, providing support for cross-platform file and printer sharing with Microsoft Windows, OS X, and other Unix.
Double free error is caused by freeing same memory location twice by calling free() on the same allocated memory. A NULL pointer dereference is a sub type of an error causing a segmentation fault. It occurs when a program attempts to read or write to memory with a NULL pointer. This design limitation was happen in a lot of software application. Found above vulnerabilities occurs in Samba server. For more details, please refer below:
Unprivileged adding of CNAME record causing loop in AD Internal DNS server : https://www.samba.org/samba/security/CVE-2018-14629.html
Double-free in Samba AD DC KDC with PKINIT
NULL pointer de-reference in Samba AD DC LDAP server
NULL pointer de-reference in Samba AD DC DNS servers
Samba AD DC S4U2Self Crash in experimental MIT Kerberos configuration (unsupported)
Bad password count in AD DC not always effective