Denial of Service in 389 Directory Server via CVE-2026-18453

CVE-2026-18453 is a vulnerability in the 389 Directory Server that allows for remote denial of service. The flaw stems from a missing NULL pointer check in the paged results handling logic within the op_shared_search function. An unauthenticated attacker can trigger this condition by sending a specially crafted sequence of LDAP search requests that utilize the USE_ONE_BACKEND control. When the server processes these requests in a specific manner, the lack of input validation results in a NULL pointer dereference, causing the LDAP server process to crash. This vulnerability is significant because it allows remote, unauthenticated actors to disrupt directory services with minimal interaction, potentially impacting authentication and authorization workflows that rely on the directory server.

Impact

Successful exploitation leads to a denial of service (DoS) of the 389 Directory Server. This impacts organizations relying on the server for centralized identity management, potentially preventing user authentication, service access, and administrative operations. The severity is assessed as high due to the ease of remote execution without authentication requirements.

Recommendation

• Patch 389 Directory Server to the version containing the fix for CVE-2026-18453.
• Monitor LDAP traffic for excessive or malformed search requests using the USE_ONE_BACKEND control in the request payload.
• Limit network access to the LDAP service to trusted subnets and IP addresses to prevent unauthenticated remote access.