ASA-2019-00622 – Samba: User with “get changes” permission can crash AD DC LDAP server via dirsync

Since Samba 4.0.0 Samba has implemented, in the AD DC, the "dirsync" LDAP control specified in MS-ADTS " LDAP_SERVER_DIRSYNC_OID". However, when combined with the ranged results feature specified in MS-ADTS " Range Retrieval of Attribute Values" a NULL pointer is can be de-referenced. This is a Denial of Service only, no further escalation of privilege is associated with this issue.

ASA-2019-00621 – Samba: AD DC check password script does not receive the full password

Since Samba Version 4.5.0 a Samba AD DC can use a custom command to verify the password complexity. The command can be specified with the "check password script" smb.conf parameter. This command is called when Samba handles a user password change or a new user password is set. The script receives the new cleartext password string in order to run custom password complexity checks like dictionary checks to avoid weak user passwords. When the password contains multi-byte (non-ASCII) characters, the check password script does not receive the full password string.

ASA-2019-00620 – Samba: Client code can return filenames containing path separators

Samba client code (libsmbclient) returns server-supplied filenames to calling code without checking for pathname separators (such as "/" or"../") in the server returned names. A malicious server can craft a pathname containing separators and return this to client code, causing the client to use this access local pathnames for reading or writing instead of SMB network pathnames. This access is done using the local privileges of the client. This attack can be achieved using any of SMB1/2/3 as it is not reliant on any specific SMB protocol version.

ASA-2019-00364 – Samba: A user with read access to the directory can cause a NULL pointer dereference using the paged search control

A user with read access to the LDAP server can crash the LDAP server process. Depending on the Samba version and the choice of process model, this may crash only the user's own connection.

ASA-2019-00266 – Samba: AD DC S4U2Self/S4U2Proxy unkeyed checksum

S4U2Self is an extension to Kerberos used in Active Directory to allow a service to request a kerberos ticket to itself from the Kerberos Key Distribution Center (KDC) for a non-Kerberos authenticated user (principal in Kerberos parlance). This is useful to allow internal code paths to be standardized around Kerberos. S4U2Proxy (constrained-delegation) is an extension of this mechanism allowing this impersonation to a second service over the network. It allows a privileged server that obtained a S4U2Self ticket to itself to then assert the identity of that principal to a second service and present itself as that principal to get services from the second service. There is a flaw in Samba's AD DC in the Heimdal KDC. When the Heimdal KDC checks the checksum that is placed on the S4U2Self packet by the server to protect the requested principal against modification, it does not confirm that the checksum algorithm that protects the user name (principal) in the request is keyed. This allows a man-in-the-middle attacker who can intercept the request to the KDC to modify the packet by replacing the user name (principal) in the request with any desired user name (principal) that exists in the KDC and replace the checksum protecting that name with a CRC32 checksum (which requires no prior knowledge to compute). This would allow a S4U2Self ticket requested on behalf of user name (principal) user@EXAMPLE.COM to any service to be changed to a S4U2Self ticket with a user name (principal) of Administrator@EXAMPLE.COM. This ticket would then contain the PAC of the modified user name (principal).

ASA-2019-00231 – Samba: Save registry file outside share as unprivileged user

Samba contains an RPC endpoint emulating the Windows registry service API. One of the requests, "winreg_SaveKey", is susceptible to a path/symlink traversal vulnerability. Unprivileged users can use it to create a new registry hive file anywhere they have unix permissions to create a new file within a Samba share. If they are able to create symlinks on a Samba share, they can create a new registry hive file anywhere they have write access, even outside a Samba share definition. Note - existing share restrictions such as "read only" or share ACLs do *not* prevent new registry hive files being written to the filesystem. A file may be written under any share definition wherever the user has unix permissions to create a file. Existing files cannot be overwritten using this vulnerability, only new registry hive files can be created, however the presence of existing files with a specific name can be detected. Samba writes or detects the file as the authenticated user, not as root.

ASA-2019-00230 – Samba: World writable files in Samba AD DC private/ dir

During the creation of a new Samba AD DC, files are created in a the private/ subdirectory of our install location. This directory is typically mode 0700, that is owner (root) only access. However in some upgraded installations it will have other permissions, such as 0755, because this was the default before Samba 4.8. Within this directory files are created with mode 0666, that is world-writable, including a sample krb5.conf and the list of DNS names and servicePrincipalName values to update.