CVE-2015-6908 in Mac OS X
Summary
by MITRE
The ber_get_next function in libraries/liblber/io.c in OpenLDAP 2.4.42 and earlier allows remote attackers to cause a denial of service (reachable assertion and application crash) via crafted BER data, as demonstrated by an attack against slapd.
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Analysis
by VulDB Data Team • 11/17/2024
The vulnerability identified as CVE-2015-6908 represents a critical denial of service flaw within the OpenLDAP software ecosystem, specifically affecting versions up to and including 2.4.42. This issue resides within the ber_get_next function located in the libraries/liblber/io.c file, which forms a fundamental component of the Lightweight Directory Access Protocol implementation. The vulnerability manifests when the software processes malformed Binary Encoding Rules (BER) data structures, creating a scenario where legitimate network traffic can be exploited to disrupt service availability. The attack vector involves sending specially crafted BER-encoded data packets to the slapd daemon, which serves as the OpenLDAP server process responsible for handling directory service requests.
The technical exploitation of this vulnerability occurs through an assertion failure within the ber_get_next function, which is part of the LDAP protocol's basic encoding and decoding mechanisms. When the function encounters malformed BER data, it triggers an assertion that causes the slapd process to terminate abruptly, resulting in a complete denial of service for the directory service. This assertion failure represents a classic example of improper input validation and error handling, where the software fails to properly sanitize or reject malformed data before attempting to process it. The vulnerability stems from a lack of robust bounds checking and data integrity verification within the BER parsing logic, allowing attackers to craft packets that cause the application to crash through controlled assertion failures. This type of vulnerability aligns with CWE-682, which describes incorrect use of mathematical operations, and more specifically with CWE-129, concerning insufficient bounds checking.
The operational impact of CVE-2015-6908 extends beyond simple service disruption, as it can be leveraged by malicious actors to systematically degrade directory services within organizations that rely on OpenLDAP for authentication, authorization, and directory management. The slapd daemon serves as a critical infrastructure component in many enterprise environments, supporting everything from user authentication to access control lists and service discovery mechanisms. When exploited, this vulnerability can result in cascading failures across dependent systems that rely on directory services, potentially affecting email systems, network authentication, application access controls, and other services that depend on LDAP for identity management. The remote nature of the attack means that adversaries can exploit this vulnerability from any location with network access to the target system, making it particularly dangerous for publicly exposed directory services.
Organizations affected by this vulnerability should implement immediate mitigation strategies including applying the vendor-provided security patches released after the vulnerability disclosure, which typically involve enhanced input validation and proper error handling within the BER parsing functions. Network-level mitigations such as implementing access control lists to restrict LDAP traffic to trusted sources and deploying intrusion detection systems that can identify and block malformed BER data patterns provide additional layers of protection. The vulnerability also highlights the importance of following security best practices such as implementing proper input sanitization, conducting regular security audits of core infrastructure components, and maintaining up-to-date software versions to prevent exploitation of known vulnerabilities. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique for network denial of service attacks and represents a classic example of how protocol-level vulnerabilities can be exploited to achieve system compromise through service disruption.