CVE-2018-16860 in KDC
Summary
by MITRE
A flaw was found in samba's Heimdal KDC implementation, versions 4.8.x up to, excluding 4.8.12, 4.9.x up to, excluding 4.9.8 and 4.10.x up to, excluding 4.10.3, when used in AD DC mode. A man in the middle attacker could use this flaw to intercept the request to the KDC and replace the user name (principal) in the request with any desired user name (principal) that exists in the KDC effectively obtaining a ticket for that principal.
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Analysis
by VulDB Data Team • 08/02/2024
The vulnerability identified as CVE-2018-16860 represents a critical authentication flaw within Samba's Heimdal Key Distribution Center implementation, specifically affecting Active Directory Domain Controller deployments. This security weakness stems from inadequate validation of principal names during Kerberos authentication requests, creating a pathway for sophisticated man-in-the-middle attacks that can effectively impersonate legitimate users within the domain environment. The flaw impacts multiple Samba version streams including 4.8.x (excluding 4.8.12), 4.9.x (excluding 4.9.8), and 4.10.x (excluding 4.10.3), indicating a widespread vulnerability across the Samba 4.x release family that has significant implications for enterprise security infrastructures relying on Kerberos authentication.
The technical nature of this vulnerability resides in the improper handling of principal name validation within the Kerberos Key Distribution Center component. When a client initiates a Kerberos authentication request to an Active Directory Domain Controller running affected Samba versions, the system fails to properly verify that the requested principal name matches the authenticated user identity. This validation gap allows an attacker positioned between the client and the KDC to intercept the authentication request and substitute the original principal name with an alternative valid principal name from the KDC database. The flaw operates at the protocol level where Kerberos tickets are generated, enabling the attacker to obtain valid Kerberos service tickets for the substituted principal, effectively bypassing authentication controls and gaining unauthorized access to domain resources.
The operational impact of CVE-2018-16860 extends far beyond simple credential theft, as it fundamentally compromises the integrity of the Kerberos authentication system that underpins Active Directory security. An attacker exploiting this vulnerability can escalate privileges and gain access to sensitive domain resources, including file servers, database systems, and other services protected by Kerberos authentication. The attack requires only network interception capabilities and does not necessitate prior access to the domain or knowledge of user credentials, making it particularly dangerous for environments where network traffic is not properly secured. This vulnerability directly aligns with ATT&CK technique T1550.003 for use of Kerberoasting and T1078.002 for valid accounts, as it enables unauthorized access through legitimate authentication mechanisms. Organizations may experience cascading security failures as compromised user accounts can be used to access additional systems and data, potentially leading to full domain compromise.
Organizations should immediately implement mitigation strategies including updating to patched Samba versions, deploying network segmentation to prevent man-in-the-middle attacks, and implementing additional authentication controls such as Kerberos encryption requirements and secure channel monitoring. The vulnerability demonstrates the critical importance of proper input validation and authentication flow integrity in security-critical systems, as outlined in CWE-284 for improper access control and CWE-295 for improper certificate validation. Network administrators should also consider implementing additional monitoring for unusual Kerberos ticket requests and principal name changes that could indicate exploitation attempts, while ensuring that all domain controllers are properly updated and maintained to prevent similar vulnerabilities from being exploited in the future.