CVE-2023-4091 Explained : Impact and Mitigation

This CVE record pertains to a vulnerability found in Samba that allows SMB clients to truncate files with read-only permissions under specific configurations.

Understanding CVE-2023-4091

This section will delve into the details of CVE-2023-4091, including its impact, technical aspects, affected systems, and mitigation strategies.

What is CVE-2023-4091?

The vulnerability in Samba enables 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". This issue arises when the SMB protocol allows opening files with read-only access but subsequently truncates the opened file to 0 bytes if a separate OVERWRITE create disposition request is specified by the client. The vulnerability is most prominent in configurations that bypass kernel file system permissions checks and rely solely on Samba's permissions.

The Impact of CVE-2023-4091

The impact of CVE-2023-4091 is classified as "Moderate" by Red Hat's severity rating. The CVSS v3.1 base score is 6.5, with a base severity of "MEDIUM." The vulnerability does not have a significant impact on availability but can result in high integrity issues. The attack complexity is low, and user interaction is not required for exploitation.

Technical Details of CVE-2023-4091

This section will provide a detailed overview of the vulnerability, including the vulnerability description, affected systems and versions, and the exploitation mechanism.

Vulnerability Description

The vulnerability in Samba allows SMB clients to truncate files with read-only permissions in specific configurations involving the "acl_xattr" module.

Affected Systems and Versions

The affected products include Samba versions 4.19.1, 4.18.8, and 4.17.12. Additionally, Red Hat Enterprise Linux 8 versions, 8.6 EUS, 8.8 EUS, and 9 versions are impacted.

Exploitation Mechanism

Exploiting CVE-2023-4091 involves leveraging the misconfiguration of the Samba VFS module "acl_xattr" to truncate files with read-only permissions.

Mitigation and Prevention

This section will outline the steps that can be taken to mitigate the impact of CVE-2023-4091, including immediate action items and long-term security practices.

Immediate Steps to Take

To mitigate the vulnerability, it is recommended to adjust the configuration settings of the "acl_xattr" module by setting "acl_xattr:ignore system acls = no".

Long-Term Security Practices

Implementing robust file system permissions and regularly updating Samba configurations can enhance security posture and reduce the risk of similar vulnerabilities.

Patching and Updates

Users should regularly check for patches and updates provided by Samba and Red Hat to address CVE-2023-4091 and ensure the security of their systems.