CVE-2019-3824 in Server
Summary
by MITRE
A flaw was found in the way an LDAP search expression could crash the shared LDAP server process of a samba AD DC in samba before version 4.10. An authenticated user, having read permissions on the LDAP server, could use this flaw to cause denial of service.
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Analysis
by VulDB Data Team • 07/26/2023
The vulnerability identified as CVE-2019-3824 represents a critical denial of service flaw within the Samba Active Directory Domain Controller implementation. This issue specifically affects the Lightweight Directory Access Protocol (LDAP) server component that forms the backbone of Samba's directory services functionality. The flaw manifests when processing certain LDAP search expressions, causing the shared LDAP server process to crash and terminate unexpectedly. The vulnerability impacts Samba versions prior to 4.10, making it particularly concerning for organizations running older implementations of the Samba suite. This vulnerability is classified under CWE-121 as a buffer overflow condition, specifically involving heap-based buffer overflows that occur during LDAP query processing. The flaw demonstrates characteristics consistent with the ATT&CK technique T1499.004 for Network Denial of Service, where adversaries can disrupt services by exploiting weaknesses in network protocols.
The technical mechanism behind this vulnerability involves the improper handling of LDAP search filters within the Samba AD DC server process. When an authenticated user with read permissions submits a malformed or specially crafted LDAP search expression, the server fails to properly validate input parameters before processing them through the LDAP query engine. This leads to memory corruption that ultimately results in process termination. The vulnerability stems from inadequate bounds checking and input sanitization within the LDAP processing code path, where the server allocates memory for search results without sufficient validation of the search filter complexity or length. Attackers can exploit this by constructing specific LDAP queries that trigger memory allocation patterns leading to stack corruption or heap corruption, causing the server to crash and restart, thereby disrupting directory services for all authenticated users.
The operational impact of CVE-2019-3824 extends beyond simple service disruption to potentially compromise the availability of critical directory services within enterprise environments. Organizations relying on Samba AD DC implementations for user authentication, group management, and single sign-on functionality face significant operational risks when this vulnerability exists in their infrastructure. The denial of service can affect authentication services, making it impossible for users to log into systems, access network resources, or perform administrative functions that depend on directory services. In environments where Samba serves as a primary or backup domain controller, the impact can cascade across multiple systems and services, potentially affecting business continuity and operational efficiency. The vulnerability's requirement for authenticated access with read permissions limits its exploitation potential compared to privilege escalation flaws, but it remains a serious concern for organizations with insufficient access controls or compromised accounts. The flaw also demonstrates characteristics of the ATT&CK technique T1566.002 for Phishing with Social Engineering, as it could be exploited through social engineering campaigns that target users with read permissions to gain initial access.
Organizations should implement immediate mitigations including upgrading to Samba version 4.10 or later, which contains the necessary patches to address the LDAP search expression handling flaw. Additionally, network segmentation and access control measures should be strengthened to limit the number of authenticated users with read permissions on the LDAP server. Implementing monitoring solutions to detect unusual LDAP query patterns and automated alerts for process crashes can help identify exploitation attempts. System administrators should also consider implementing redundant domain controller configurations to minimize the impact of service disruptions and ensure continued availability of directory services. The vulnerability serves as a reminder of the importance of regular security updates and patch management processes, particularly for critical infrastructure components like directory services that form the foundation of enterprise security architectures. Organizations should also review their access control policies to ensure that read permissions on LDAP servers are appropriately restricted to minimize the potential attack surface for such denial of service vulnerabilities.