CVE-2011-4079 in OpenLDAP
Summary
by MITRE
Off-by-one error in the UTF8StringNormalize function in OpenLDAP 2.4.26 and earlier allows remote attackers to cause a denial of service (slapd crash) via a zero-length string that triggers a heap-based buffer overflow, as demonstrated using an empty postalAddressAttribute value in an LDIF entry.
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Analysis
by VulDB Data Team • 01/05/2025
The vulnerability CVE-2011-4079 represents a critical off-by-one error within the UTF8StringNormalize function of OpenLDAP versions 2.4.26 and earlier. This flaw exists in the core directory service implementation that handles Lightweight Directory Access Protocol operations, specifically affecting the slapd daemon responsible for processing directory requests. The issue manifests when processing zero-length strings during UTF-8 normalization operations, creating a condition where memory boundaries are improperly validated.
The technical implementation of this vulnerability stems from improper bounds checking within the UTF8StringNormalize function that processes string data for directory attributes. When a zero-length string is encountered, particularly in the postalAddressAttribute field of LDIF entries, the function fails to properly account for the boundary conditions of heap memory allocation. This results in a heap-based buffer overflow that corrupts adjacent memory regions and ultimately causes the slapd process to crash. The vulnerability operates through the LDAP protocol's attribute processing pipeline where malformed data triggers the flawed normalization routine.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable more sophisticated attack vectors. Remote attackers can exploit this weakness to cause persistent denial of service against LDAP directory services, affecting authentication systems, user management platforms, and enterprise directory infrastructure that relies on OpenLDAP. The crash occurs during normal directory operations when processing valid but malformed LDIF entries, making detection difficult and potentially allowing for automated exploitation. Organizations using affected OpenLDAP versions face significant risk to directory availability and potentially broader system stability.
Mitigation strategies for CVE-2011-4079 require immediate patching of affected OpenLDAP installations to versions 2.4.27 or later where the off-by-one error has been corrected. System administrators should implement network segmentation and access controls to limit exposure to untrusted LDAP clients while monitoring for suspicious LDIF entry patterns. The vulnerability maps to CWE-129 as an improper input validation issue and aligns with ATT&CK technique T1499 for endpoint denial of service attacks. Organizations should also consider implementing intrusion detection systems to monitor for malformed LDAP requests and establish incident response procedures for directory service disruptions. Regular security assessments of directory services and comprehensive patch management programs are essential to prevent exploitation of similar memory corruption vulnerabilities in directory service implementations.