CVE-2019-3870

A vulnerability was found in Samba from version (including) 4.9 to versions before 4.9.6 and 4.10.2. During the creation of a new Samba AD DC, files are created in a private subdirectory of the 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, which is world-writable, including a sample krb5.conf, and the list of DNS names and servicePrincipalName values to update.

Weakness

During installation, installed file permissions are set to allow anyone to modify those files.

Affected Software

Potential Mitigations

• Compartmentalize the system to have “safe” areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.
• Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/1.html
• https://cwe.mitre.org/data/definitions/127.html
• https://cwe.mitre.org/data/definitions/81.html

References

• https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2019-3870
• https://bugzilla.samba.org/show_bug.cgi?id=13834
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/6354GALK73CZWQKFUG7AWB6EIEGFMF62/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JTJVFA3RZ6G2IZDTVKLHRMX6QBYA4GPA/
• https://support.f5.com/csp/article/K20804356
• https://www.samba.org/samba/security/CVE-2019-3870.html
• https://www.synology.com/security/advisory/Synology_SA_19_15