CVE-2018-5730 in Kerberos 5
Summary
by MITRE
MIT krb5 1.6 or later allows an authenticated kadmin with permission to add principals to an LDAP Kerberos database to circumvent a DN containership check by supplying both a "linkdn" and "containerdn" database argument, or by supplying a DN string which is a left extension of a container DN string but is not hierarchically within the container DN.
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Analysis
by VulDB Data Team • 05/05/2025
The vulnerability identified as CVE-2018-5730 represents a critical authorization bypass flaw within the MIT krb5 implementation when integrated with LDAP Kerberos databases. This issue affects versions 1.6 and later of the Kerberos implementation, specifically targeting the kadmin administrative tool's handling of database container checks. The flaw exists in the LDAP database backend where the system performs container validation during principal creation operations, creating a potential pathway for unauthorized privilege escalation through improper directory naming validation.
The technical exploitation of this vulnerability relies on manipulating the LDAP database configuration parameters during principal creation operations. An authenticated kadmin user with appropriate permissions can circumvent the standard DN (Distinguished Name) containership validation by providing either a "linkdn" and "containerdn" database argument combination or by supplying a DN string that appears to be a left extension of a container DN but exists outside the proper hierarchical container structure. This bypass occurs because the validation logic fails to properly verify that the provided DN is genuinely contained within the designated container boundaries, allowing attackers to create principals in unauthorized locations.
The operational impact of this vulnerability extends beyond simple privilege escalation to potentially compromise the entire Kerberos infrastructure. An attacker with kadmin access can manipulate the LDAP directory structure to create principals in locations where they should not have authorization, potentially leading to unauthorized access to services, impersonation of legitimate users, or disruption of the authentication system. This flaw undermines the fundamental security model of Kerberos by allowing unauthorized directory placement of principals, which could enable lateral movement within the network infrastructure and provide persistent access to privileged resources.
This vulnerability aligns with CWE-22, which addresses improper limitation of a pathname to a restricted directory, and demonstrates how directory traversal and containment checks can be bypassed in authentication systems. The flaw also corresponds to ATT&CK technique T1078 which covers valid accounts and privilege escalation through legitimate administrative tools. Organizations using MIT krb5 with LDAP backends face significant risk as this vulnerability can be exploited without requiring additional privileges beyond authentication to the kadmin interface. The attack vector is particularly concerning because it leverages legitimate administrative functionality to bypass security controls, making detection more challenging and potentially allowing attackers to maintain long-term access to the Kerberos infrastructure.
Mitigation strategies should focus on immediate patching of affected MIT krb5 versions to address the LDAP container validation logic. Organizations should also implement strict monitoring of kadmin operations, particularly principal creation activities, with alerts configured for unusual DN patterns or container modifications. Additional controls include implementing role-based access controls that limit which users can perform principal creation operations, regular auditing of LDAP directory structures, and ensuring that administrative accounts are properly protected through multi-factor authentication. Network segmentation and limiting direct access to LDAP databases from administrative systems can also reduce the attack surface. The vulnerability highlights the importance of proper input validation and containment checks in authentication systems, emphasizing that even legitimate administrative tools must maintain strict boundaries to prevent unauthorized privilege escalation.