CVE-2026-18453 Red Hat CVE debrief

Who should care

Defenders responsible for Red Hat Directory Server 11 instances should assess exposure and prioritize patching or mitigation to prevent potential denial-of-service attacks. This includes verifying the exposure of Red Hat Directory Server 11 instances, applying patches or mitigations, and monitoring LDAP server logs for suspicious activity. Additionally, defenders should review vendor guidance and conduct asset inventory to identify potentially affected 389

Why it matters

CVE-2026-18453 is a high-severity vulnerability in 389 Directory Server that allows an unauthenticated remote attacker to crash the LDAP server, resulting in denial of service. Defenders responsible for Red Hat Directory Server 11 instances should assess exposure and prioritize patching or mitigation to prevent potential attacks.

• Potential denial-of-service attacks against LDAP servers
• Verification of Red Hat Directory Server 11 instance exposure
• Patching or mitigation prioritization to prevent attacks
• Monitoring LDAP server logs for suspicious activity

Technical summary

A missing NULL pointer check in the paged results handling of op_shared_search in 389 Directory Server allows an unauthenticated remote attacker to crash the LDAP server by sending a crafted sequence of search requests using the USE_ONE_BACKEND control. This issue affects Red Hat Directory Server 11 instances and defenders should prioritize verifying exposure and applying patches or mitigations to prevent potential denial-of-service attacks. The vulnerability has a CVSS score of 7.5 and is classified as HIGH severity.

Defensive priority

Defenders should prioritize verifying exposure of Red Hat Directory Server 11 instances and applying patches or mitigations to prevent potential denial-of-service attacks.

Recommended defensive actions

• Verify exposure of Red Hat Directory Server 11 instances
• Apply patches or mitigations to prevent potential denial-of-service attacks
• Monitor LDAP server logs for suspicious activity
• Implement compensating controls to detect and prevent similar attacks
• Review vendor guidance for Red Hat Directory Server 11 instances
• Conduct asset inventory to identify potentially affected systems
• Track exceptions and retest remediated assets

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its description, CVSS score, and affected products. The vulnerability is caused by a missing NULL pointer check in the paged results handling of op_shared_search in 389 Directory Server. Defenders should verify the exposure of Red Hat Directory Server 11 instances and apply patches or mitigations to prevent potential denial-of-service attacks. The CVE record was published on 2026-09-07T15:17:31.017Z and has not been modified since then.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.