CVE-2023-4091

A vulnerability was discovered in Samba, where the flaw allows SMB clients to truncate files, even with read-only permissions when the Samba VFS module acl_xattr is configured with acl_xattr:ignore system acls = yes. The SMB protocol allows opening files when the client requests read-only access but then implicitly truncates the opened file to 0 bytes if the client specifies a separate OVERWRITE create disposition request. The issue arises in configurations that bypass kernel file system permissions checks, relying solely on Sambas permissions.

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://access.redhat.com/errata/RHSA-2023:6209
• https://access.redhat.com/errata/RHSA-2023:6744
• https://access.redhat.com/errata/RHSA-2023:7371
• https://access.redhat.com/errata/RHSA-2023:7408
• https://access.redhat.com/errata/RHSA-2023:7464
• https://access.redhat.com/errata/RHSA-2023:7467
• https://access.redhat.com/security/cve/CVE-2023-4091
• https://bugzilla.redhat.com/show_bug.cgi?id=2241882
• https://bugzilla.samba.org/show_bug.cgi?id=15439
• https://www.samba.org/samba/security/CVE-2023-4091.html