CVE-2015-7540 in Samba
Summary
by MITRE
The LDAP server in the AD domain controller in Samba 4.x before 4.1.22 does not check return values to ensure successful ASN.1 memory allocation, which allows remote attackers to cause a denial of service (memory consumption and daemon crash) via crafted packets.
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Analysis
by VulDB Data Team • 07/02/2022
The vulnerability identified as CVE-2015-7540 affects the Active Directory domain controller functionality within Samba 4.x versions prior to 4.1.22. This issue resides in the Lightweight Directory Access Protocol (LDAP) server implementation that forms part of the Samba suite's directory services. The flaw represents a classic memory management error that can be exploited remotely to disrupt service availability. The vulnerability specifically impacts systems running Samba 4.x servers that function as domain controllers, making it particularly concerning for enterprise environments that rely heavily on Active Directory integration. Organizations using older Samba versions for directory services and authentication are at risk of experiencing service disruption and potential system instability.
The technical root cause of this vulnerability stems from inadequate error handling within the ASN.1 (Abstract Syntax Notation One) memory allocation routines used by the LDAP server. ASN.1 is a standard interface description language used for defining data structures that can be serialized and deserialized in a platform-independent manner, commonly used in directory services and network protocols. When processing incoming LDAP requests, the Samba LDAP server fails to properly validate the return values from memory allocation functions, specifically those related to ASN.1 encoding operations. This lack of validation means that if memory allocation fails due to resource constraints or malicious input, the server continues processing without proper error recovery mechanisms. The flaw creates a condition where attackers can craft specially formatted LDAP packets that trigger memory allocation failures, leading to uncontrolled resource consumption and ultimately causing the LDAP daemon to crash.
The operational impact of CVE-2015-7540 extends beyond simple service disruption to encompass broader security implications for enterprise infrastructure. When exploited, this vulnerability can result in sustained denial of service conditions that may persist until manual intervention or system restart occurs. The memory consumption aspect of the attack can be particularly insidious as it may gradually consume available system resources, potentially leading to cascading failures across dependent services. For organizations relying on Samba-based domain controllers, this vulnerability could compromise authentication services and directory access, affecting user logins, group policy application, and other directory-dependent operations. The remote nature of the attack means that even systems not directly connected to the internet could be compromised if attackers can reach the domain controller through network traversal or lateral movement. This vulnerability aligns with CWE-704, which describes improper handling of memory allocation failures, and represents a clear violation of secure coding practices that should prevent such conditions from occurring.
Mitigation strategies for CVE-2015-7540 primarily focus on immediate version updates and operational hardening measures. The most effective solution involves upgrading to Samba 4.1.22 or later versions where the memory allocation validation has been corrected. System administrators should prioritize patching operations while ensuring proper testing in staging environments to prevent unexpected service interruptions. Network segmentation and access controls should be implemented to limit exposure of domain controllers to untrusted networks, reducing the attack surface available to potential exploiters. Monitoring and logging configurations should be enhanced to detect anomalous LDAP traffic patterns that might indicate exploitation attempts. Implementing intrusion detection systems that can identify crafted LDAP packets and setting up automated alerting for unusual memory consumption patterns on domain controller systems provides additional layers of defense. The vulnerability demonstrates the importance of adhering to the principle of least privilege in network architecture and implementing proper input validation as outlined in the ATT&CK framework's defense in depth strategies. Organizations should also consider implementing rate limiting and connection throttling mechanisms for LDAP services to mitigate the impact of potential exploitation attempts.