CVE-2026-18453: NULL Pointer Dereference in Red Hat Red Hat Directory Server 11.5 E4S for RHEL 8

The vulnerability CVE-2026-18453 affects 389 Directory Server, specifically in the handling of paged results within the op_shared_search function. Due to a missing NULL pointer check, an unauthenticated remote attacker can trigger a NULL pointer dereference by sending a specially crafted sequence of LDAP search requests that use the USE_ONE_BACKEND control. This leads to a denial of service by crashing the LDAP server. The issue is rated with a CVSS 3.1 base score of 7.5 (high severity) and has been addressed by Red Hat in an update to the 389-ds-base package as part of their Extended Life Cycle Support for RHEL 7. The vendor advisory provides details on the fix and affected product versions.

Successful exploitation allows an unauthenticated remote attacker to cause a denial of service by crashing the LDAP server. There is no impact on confidentiality or integrity, but availability is severely affected due to the server crash.

Red Hat has released an official security update for the 389-ds-base package that addresses this vulnerability. Users should apply the update as described in the Red Hat advisory RHSA-2026:64771 to remediate the issue. The advisory covers Red Hat Enterprise Linux Server Extended Life Cycle Support 7 on multiple architectures. Patch status is confirmed as fixed in the updated packages referenced in the advisory. No additional mitigation is required once the update is applied.