CVE-2019-12435 in Samba
Summary
by MITRE
Samba 4.9.x before 4.9.9 and 4.10.x before 4.10.5 has a NULL pointer dereference, leading to Denial of Service. This is related to the AD DC DNS management server (dnsserver) RPC server process.
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Analysis
by VulDB Data Team • 10/06/2023
The vulnerability identified as CVE-2019-12435 represents a critical NULL pointer dereference flaw affecting Samba implementations version 4.9.x prior to 4.9.9 and 4.10.x prior to 4.10.5. This issue specifically targets the Active Directory Domain Controller DNS management server component known as dnsserver RPC server process, which forms a crucial part of Samba's directory services functionality. The flaw manifests when the DNS server component processes certain malformed RPC requests, creating a condition where a null pointer is dereferenced during normal operation. This vulnerability falls under the CWE-476 category of NULL Pointer Dereference, which is classified as a common weakness in software security implementations.
The technical exploitation of this vulnerability occurs within the dnsserver RPC server process that handles DNS zone management operations in Active Directory environments. When an attacker crafts specific RPC requests targeting DNS management functionality, the server fails to properly validate incoming parameters before attempting to dereference pointers that may be null. This results in an immediate crash of the dnsserver process, which is part of the larger Samba AD DC service. The flaw does not appear to enable arbitrary code execution or privilege escalation, but rather focuses on disrupting service availability through controlled process termination. The vulnerability is particularly concerning in enterprise environments where AD DC services are critical infrastructure components.
The operational impact of CVE-2019-12435 extends beyond simple service disruption to potentially compromise business continuity in enterprise networks. When the dnsserver process crashes, it affects DNS resolution capabilities within the Active Directory domain, which can cascade into broader network service failures. This denial of service condition can affect authentication services, domain controller replication, and general network connectivity for domain-joined systems. The vulnerability affects organizations using Samba as their primary directory service implementation, particularly those managing large AD environments where DNS services are heavily utilized. Network administrators may experience intermittent service interruptions that are difficult to diagnose since the crash occurs in the DNS management subsystem rather than the primary AD services.
Organizations should implement immediate mitigations including applying the patched versions of Samba 4.9.9 and 4.10.5, which contain the necessary code modifications to properly validate RPC request parameters before pointer dereference operations. Network segmentation and monitoring solutions should be enhanced to detect unusual RPC traffic patterns that may indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1499.004 for Network Denial of Service, which targets service availability through various mechanisms. System administrators should also consider implementing IDS/IPS rules that monitor for specific RPC patterns associated with this vulnerability, as well as establishing robust monitoring for dnsserver process stability. Regular patch management processes should be reinforced to ensure timely deployment of security updates, particularly for critical infrastructure components like directory services that form the foundation of enterprise network security.