CVE-2019-12436 in Samba
Summary
by MITRE
Samba 4.10.x before 4.10.5 has a NULL pointer dereference, leading to an AD DC LDAP server Denial of Service. This is related to an attacker using the paged search control. The attacker must have directory read access in order to attempt an exploit.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 10/06/2023
The vulnerability identified as CVE-2019-12436 represents a critical denial of service weakness in Samba Active Directory Domain Controller implementations. This flaw exists within Samba versions 4.10.0 through 4.10.4, specifically affecting the LDAP server component that handles directory queries. The issue manifests as a NULL pointer dereference condition that occurs when processing paged search controls, which are standard LDAP extensions used to manage large result sets efficiently. The vulnerability stems from inadequate input validation within the LDAP processing pipeline, where the system fails to properly handle malformed or unexpected control parameters during directory searches.
The technical exploitation of this vulnerability requires an attacker to possess valid directory read credentials within the target Active Directory environment, establishing a baseline for authenticated access. However, the impact extends beyond simple credential compromise since the attacker can leverage the paged search control mechanism to trigger the NULL pointer dereference. This control is commonly used by legitimate clients to retrieve large directory objects in manageable chunks, making the vulnerability particularly dangerous as it can be triggered through normal operational activities. The dereference occurs when the LDAP server attempts to process a specially crafted paged search request that contains malformed control parameters, causing the application to crash and restart the LDAP service.
From an operational perspective, this vulnerability creates a significant risk for organizations relying on Samba AD DC implementations, as it can be exploited to disrupt directory services without requiring elevated privileges or complex attack vectors. The denial of service impact effectively prevents legitimate users from accessing directory services, potentially cascading into broader service disruptions throughout the enterprise infrastructure. The vulnerability aligns with CWE-476, which categorizes NULL pointer dereference conditions as a fundamental programming error that can lead to application crashes and service interruptions. Network-based attacks can be executed through standard LDAP client tools, making the exploitation relatively straightforward for threat actors with basic directory access credentials.
Organizations should immediately implement mitigations including applying the patched Samba version 4.10.5 or later, which contains the necessary code modifications to properly validate paged search controls. Network segmentation and access control measures can help limit the exposure by restricting LDAP service access to trusted networks and authorized client systems. Monitoring should focus on detecting unusual LDAP traffic patterns, particularly those involving paged search controls, which can serve as indicators of exploitation attempts. Security teams should also consider implementing intrusion detection systems capable of identifying malformed LDAP control parameters. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service tactics, as it allows attackers to disrupt services while potentially serving as a precursor to more sophisticated attacks targeting directory service integrity and availability.