A critical flaw (CVE-2023-42670) has been discovered in Samba, a popular open-source software suite that offers file sharing and print services for Microsoft Windows clients. Due to this vulnerability, multiple incompatible Remote Procedure Call (RPC) listeners can be initiated, causing disruptions in Active Directory Domain Controller (AD DC) service.

The Problem

Under high load or unresponsive conditions, Samba's RPC server might inadvertently initialize servers intended for non-AD DC purposes (such as NT4-emulation "classic DCs") and compete for the allocation of the same Unix domain sockets. Consequently, AD DC would deliver partial query responses, causing problems when using tools like Active Directory Users.

This vulnerability creates an opportunity for an attacker to disrupt the normal functioning of AD DC services, affecting file sharing reliability as well as user access and authentication in multi-platform, networked environments.

Exploit Details

When Samba calculates the number of RPC services to instantiate, it evaluates the configured characteristics for each service. However, due to improper handling and validation, it inadvertently instantiates incompatible listeners for multiple services, leading to the issue mentioned above.

To better understand the underlying problem, here is a simplified code snippet from Samba's RPC server:

// Simple example of problematic configuration
int num_RPC_services = ;
for (int i = ; i < MAX_SERVICES; i++) {
    if (is_RPC_service[i] && !is_AD_DC_service[i]) {
        num_RPC_services++;
    }
}
if (num_RPC_services > ) {
    initialize_incompatible_listeners();
}

As evident from the code snippet, Samba erroneously initializes incompatible listeners due to the improper evaluation of the configuration settings during the RPC service instantiation.

Original References

For a detailed technical analysis of this vulnerability, refer to the Samba project's official bug report and the corresponding entry in the Common Vulnerabilities and Exposures (CVE) database:

- Samba Bug Report: https://bugzilla.samba.org/show_bug.cgi?id=CVE-2023-42670
- CVE Entry: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-42670

Mitigation

As of now, no official patch has been released by the Samba project team to address this vulnerability directly. Until a patch is made available, organizations are advised to closely monitor their Samba deployments and ensure that proper network perimeter defense mechanisms, such as firewalls and intrusion detection systems, are in place to minimize the risk of exploitation of this flaw.

Consider monitoring for events or log entries indicating RPC server instability or high load, and keep abreast of the latest news and updates on the Samba project's official channels for further mitigation advice and patch announcements.

Conclusion

CVE-2023-42670 is a severe flaw in Samba that can potentially cause disruptions in AD DC services, affecting the reliability of file sharing as well as user access and authentication. To protect their networks and systems against this vulnerability, organizations should monitor their Samba deployments closely and ensure proper network perimeter defenses are in place while waiting for an official patch release.

Timeline

Published on: 11/03/2023 08:15:07 UTC
Last modified on: 11/24/2023 09:15:08 UTC