CVE-2018-5729 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 cause a denial of service (NULL pointer dereference) or bypass a DN container check by supplying tagged data that is internal to the database module.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/05/2025
The vulnerability identified as CVE-2018-5729 affects MIT Kerberos 5 versions 1.6 and later when configured to use an LDAP backend for storing Kerberos principals. This issue represents a critical security flaw that can be exploited by authenticated attackers who possess sufficient privileges to add new principals to the LDAP database. The vulnerability stems from inadequate input validation within the database module that handles LDAP operations, specifically when processing tagged data that is internal to the LDAP database structure.
The technical flaw manifests as a NULL pointer dereference condition that occurs when the kadmin utility processes malformed or unexpected tagged data within the LDAP database module. This particular vulnerability falls under CWE-476 which categorizes NULL pointer dereference as a common weakness in software security. When an attacker supplies specially crafted tagged data that bypasses normal validation checks, the system attempts to dereference a NULL pointer during the principal addition process, resulting in a denial of service condition that crashes the kadmin service or entire Kerberos infrastructure.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable more sophisticated attacks. An authenticated attacker with kadmin permissions can exploit this flaw to cause denial of service against the Kerberos administration service, effectively preventing legitimate administrators from managing principals or performing essential administrative functions. Additionally, the vulnerability allows bypassing DN container checks, which are critical security controls that ensure principals are added to appropriate organizational units within the LDAP directory structure. This bypass capability could potentially allow attackers to place principals in unauthorized locations within the directory hierarchy, undermining the security model of the Kerberos deployment.
The exploitation of this vulnerability aligns with ATT&CK technique T1078 which covers valid accounts and privilege escalation through legitimate credentials. Attackers can leverage their existing kadmin privileges to perform the denial of service attack or to manipulate the LDAP directory structure in ways that could compromise the integrity of the Kerberos realm. Organizations using LDAP-backed Kerberos deployments are particularly vulnerable as this flaw affects the core database interaction mechanisms that are fundamental to Kerberos operations.
Mitigation strategies for CVE-2018-5729 should include immediate patching of affected MIT Kerberos installations to versions that address the NULL pointer dereference and LDAP validation issues. Administrators should also implement additional monitoring of kadmin operations and LDAP database modifications to detect anomalous behavior that might indicate exploitation attempts. Network segmentation and privilege separation can help limit the impact if an attacker does gain access to kadmin credentials. The vulnerability demonstrates the importance of thorough input validation in database interaction modules and highlights the need for robust security testing of authentication infrastructure components that handle external data sources. Organizations should also review their LDAP directory permissions and implement proper access controls to minimize the potential damage from privilege escalation attacks targeting Kerberos administration functions.