CVE-2001-0977 in OpenLDAP
Summary
by MITRE
slapd in OpenLDAP 1.x before 1.2.12, and 2.x before 2.0.8, allows remote attackers to cause a denial of service (crash) via an invalid Basic Encoding Rules (BER) length field.
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Analysis
by VulDB Data Team • 12/15/2024
The vulnerability identified as CVE-2001-0977 represents a critical denial of service flaw in the OpenLDAP slapd daemon, which serves as the core component for directory services in the OpenLDAP implementation. This vulnerability affects versions 1.x prior to 1.2.12 and 2.x prior to 2.0.8, making it one of the earlier documented security issues in the OpenLDAP ecosystem. The flaw specifically targets the Basic Encoding Rules (BER) parsing mechanism that is fundamental to LDAP protocol communication, where slapd processes incoming requests from remote clients. The vulnerability arises from inadequate validation of BER length fields during the parsing of LDAP messages, creating an opportunity for malicious actors to exploit the protocol implementation and disrupt service availability.
The technical root cause of this vulnerability lies in the improper handling of BER length fields within the slapd daemon's message parsing routines. When a remote attacker sends a malformed LDAP request containing an invalid BER length field, the slapd process fails to properly validate this input before attempting to process the message. This lack of input sanitization leads to memory corruption or unexpected behavior in the parsing logic, ultimately causing the daemon to crash and terminate its operation. The vulnerability specifically targets the BER decoding process where length fields are used to determine the size of encoded values, and when these fields contain invalid or malformed values, the parser enters an undefined state that results in system instability and service termination.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by remote attackers without requiring authentication or specialized privileges. This makes it particularly dangerous in networked environments where LDAP services are exposed to untrusted networks or clients. The denial of service condition affects the availability of directory services, potentially impacting authentication, authorization, and directory lookup functions that depend on the LDAP infrastructure. Organizations relying on OpenLDAP for critical directory services may experience significant operational disruption, especially in environments where LDAP is used for user authentication, system configuration management, or enterprise directory services. The vulnerability's exploitation can be automated and does not require deep technical knowledge, making it a preferred attack vector for malicious actors seeking to disrupt services.
Mitigation strategies for this vulnerability should focus on immediate patching of affected OpenLDAP installations to versions 1.2.12 or 2.0.8 and later, which contain the necessary fixes for BER length field validation. Network administrators should implement proper firewall rules to restrict access to LDAP ports (typically 389 for unencrypted connections and 636 for SSL/TLS) to trusted networks only, reducing the attack surface. Additionally, monitoring systems should be configured to detect unusual patterns of LDAP traffic that might indicate exploitation attempts, and intrusion detection systems can be tuned to alert on malformed BER structures. From a security standards perspective, this vulnerability aligns with CWE-129, which addresses improper validation of length fields, and can be mapped to ATT&CK technique T1499.1 for network denial of service attacks. Organizations should also consider implementing redundant LDAP services or failover mechanisms to maintain directory service availability during patching operations. The vulnerability demonstrates the importance of robust input validation in protocol implementations and serves as a reminder of the critical nature of proper BER handling in LDAP services, particularly in enterprise environments where directory services form the backbone of authentication infrastructure.