Research Release Highlight - Changes to SMB Kerberos
Research Release Highlight - Changes to SMB Kerberos Summary Kerberos has been the default authentication mechanism for domain connected Windows devices since Windows 2008. Tenable credentialed scans of Windows targets support an explicit Kerberos credential type. The explicit credential, which names the DC and domain name, frees the Nessus sensor from having to be connected to the Windows domain being scanned and allows the scanner to be hosted on Linux or MacOS as well. The nature of this explicit Kerberos credential type has widely led to the expectation that a Kerberos scan of Windows will never use NTLM. That is not true. Currently Kerberos Windows scans will fail over to using NTLM if Kerberos does not succeed. The Kerberos protocol depends on time synchronization, FQDN target specification and bi-directional DNS name resolution, but NTLM does not. Tenable fails over to NTLM to preserve scan continuity where Kerberos on the target or scanner may not be configured correctly. As each Windows credential is tried, if Kerberos fails, a second attempt will be made using NTLM. Change We are changing Windows scans so that a scan will try all Windows credentials first before trying them again using NTLM if the credential set contains at least one Kerberos credential. This change also extends our Kerberos coverage to include Windows Configuration Manager and Active Directory Service Interfaces (ADSI) scans. Impact In certain customer environments where a single service credential (username/password) is used across multiple domains the current failover behavior causes NTLM to be used prematurely when it is possible that a subsequent Kerberos credential targeting a different domain might succeed. The change here favors Kerberos first and only fails over to NTLM after all credentials have been tried. Customers can also modify their SCCM (Windows Configuration Manager) credentials to include the domain controller's FQDN to allow those scans to use Kerberos. The net effect of these changes will be reduced dependency on NTLM in Windows scans and should produce better results in some cases. Target Release Date 07/16/2025