CVE-2026-18453

A flaw was found in 389 Directory Server. A missing NULL pointer check in the paged results handling of op_shared_search allows an unauthenticated remote attacker to crash the LDAP server by sending a crafted sequence of search requests using the USE_ONE_BACKEND control, resulting in denial of service.

This issue is rated Important because a remote attacker with network access to the LDAP service can crash the directory server process without authenticating, under default configuration. Successful exploitation completely stops directory lookups and authentication that depend on this service until the process is restarted, and the attack is easy to repeat. There is no impact on confidentiality or integrity: the fault is a crash only and does not leak or modify directory data. Environments that disable anonymous LDAP access remove the unauthenticated path, but any authenticated client that can send search requests can still trigger the same crash. Deployments that expose LDAP only to trusted networks reduce the practical attack surface, but do not change the underlying impact when a client can reach the service.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.