CVE-2026-103885 in Directory LDAP API
Summary
by MITRE • 10/02/2026
Asymmetric Resource Consumption vulnerability in Apache Directory LDAP API.
A LDAP server using the LDAP API (like Apache DS) may consume 100% of a CPU core indefinitely when processing some badly crafted Telephone Numbers.
This issue affects Apache Directory LDAP API: from 2.1.0 before 2.1.9.
Users are recommended to upgrade to version 2.1.9, which fixes the issue.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/02/2026
The vulnerability identified as an asymmetric resource consumption flaw within the Apache Directory LDAP API represents a significant availability risk for systems relying on this library for Lightweight Directory Access Protocol operations. This specific defect impacts versions of the Apache Directory LDAP API ranging from 2.1.0 up to, but not including, version 2.1.9. The core issue arises during the parsing and validation phase of telephone number attributes within directory entries. When a server utilizing this API processes specially crafted or malformed telephone numbers, it enters an inefficient computational loop that fails to terminate under normal conditions. This behavior leads to excessive CPU utilization, potentially consuming one hundred percent of a single processor core indefinitely until the process is manually terminated or the system resource limits are triggered.
From a technical perspective, this flaw aligns with CWE-400, which describes Uncontrolled Resource Consumption. The underlying mechanism likely involves regular expression processing or string manipulation logic that exhibits catastrophic backtracking when presented with specific patterns of characters in the telephone number field. Instead of rejecting invalid input efficiently through early validation checks, the parser engages in exhaustive recursive matching attempts. This results in a denial of service condition where legitimate services become unresponsive due to resource exhaustion. The attack vector is typically remote if the LDAP server exposes its interface to untrusted networks, allowing an attacker to send crafted requests that trigger this CPU spike without requiring authentication or with minimal privileges depending on the specific configuration and access controls implemented by the directory administrator.
The operational impact of this vulnerability extends beyond simple performance degradation. In production environments where Apache Directory Server or similar LDAP implementations are used for identity management, single sign-on, or application authorization, a sustained denial of service can disrupt critical business processes. Users may be unable to authenticate, applications may fail to retrieve necessary directory attributes, and system monitoring tools might generate false positives regarding infrastructure health due to the abnormal CPU usage patterns. Furthermore, because the vulnerability targets a specific data type within LDAP entries, it highlights the importance of rigorous input validation at the API layer rather than relying solely on higher-level application logic or database constraints for security enforcement.
Mitigation strategies primarily involve upgrading the affected software component as soon as possible. The maintainers have addressed this issue in version 2.1.9 by correcting the parsing logic to handle malformed telephone numbers efficiently, likely through optimized regular expressions or explicit length and format checks that prevent infinite loops. Organizations should prioritize patching their LDAP API dependencies across all environments where Apache Directory Server is deployed. In addition to upgrading, administrators can implement network-level controls such as rate limiting on LDAP connections to mitigate the impact of potential exploitation attempts while patches are being applied. Input validation at the application layer connecting to the directory service also serves as a secondary defense mechanism, ensuring that only well-formed data reaches the vulnerable API components.
This incident underscores the broader security principle that library vulnerabilities can have disproportionate effects on system availability even if they do not directly compromise confidentiality or integrity. It is classified under ATT&CK technique T1499, Endpoint Denial of Service, specifically reflecting resource exhaustion via software flaws. Security teams should review their dependency management processes to ensure timely updates for core infrastructure libraries like Apache Directory LDAP API. Regular vulnerability scanning and penetration testing that include fuzzing of directory attributes can help identify similar implementation weaknesses before they are exploited in the wild. Maintaining an up-to-date inventory of all third-party components is essential for managing these types of asymmetric resource consumption risks effectively.