CVE-2026-11788: 389 Directory Server Unauthenticated Denial-of-Service via Memory Allocation Flaw

Technical summary

CVE-2026-11788 is a null pointer dereference vulnerability (CWE-476) in the dereference control plugin of 389 Directory Server. The flaw occurs because the plugin does not validate successful allocation of a BER (Basic Encoding Rules) structure before dereferencing it. When the system experiences memory pressure, the allocation can fail silently, but the code proceeds to use the invalid pointer, resulting in a denial-of-service condition. The vulnerability is remotely exploitable over the network without authentication.

Business impact

This vulnerability enables unauthenticated remote denial-of-service attacks against 389 Directory Server deployments. Organizations relying on Directory Server for LDAP authentication and directory services face service disruption risk, particularly in environments where memory resources are constrained or during high-load periods. Repeated or sustained attacks could prevent legitimate users from authenticating, impacting business continuity and dependent applications.

Affected systems

Red Hat 389 Directory Server and Red Hat Enterprise Linux installations that include Directory Server are affected. The vulnerability impacts multiple RHEL versions bundled with vulnerable Directory Server releases. Determine your specific Directory Server version and RHEL release to assess exposure within your infrastructure.

Exploitability

The vulnerability has a CVSS 3.1 score of 5.9 (Medium severity) with an attack vector of network, no authentication required, but elevated attack complexity. The requirement for system memory pressure raises the bar for reliable exploitation compared to trivial denial-of-service attacks. However, in production environments with predictable or heavy workloads, the memory pressure condition may be achievable or present intermittently, making the vulnerability practically exploitable for a motivated attacker.

Remediation

Apply security updates from Red Hat that address this allocation failure check in the dereference control plugin. Coordinate patching across your Directory Server and Enterprise Linux infrastructure. Verify against the vendor advisory for specific patched version numbers and any interim workarounds for environments where immediate patching is not feasible.

Patch guidance

Contact Red Hat or consult their security advisory for CVE-2026-11788 to obtain the specific patched Directory Server version for your RHEL release. Test patches in a non-production environment before broad deployment to ensure compatibility with your authentication and directory infrastructure. Prioritize patching Directory Servers exposed to untrusted network segments.

Detection guidance

Monitor Directory Server logs for unexpected crashes or restarts, particularly correlated with high memory utilization or failed authentication attempts from unfamiliar sources. Network-based detection is challenging since the attack is a memory-exhaustion trigger, but observe for sustained connection attempts to LDAP ports (389/636) from external IP ranges. Implement resource monitoring to alert on abnormal memory consumption patterns on Directory Server systems.

Why prioritize this

Although the CVSS score is Medium (5.9), prioritize this vulnerability because it affects core authentication infrastructure and requires no credentials to exploit. The denial-of-service impact can cascade across dependent systems. However, the attack complexity requirement for memory pressure conditions and lack of KEV listing suggests lower active exploitation prevalence; defer non-critical systems behind the patch for Directory Servers handling authentication for production services.

Risk score, explained

The CVSS 3.1 score of 5.9 reflects the network-exploitable, unauthenticated nature of the attack (elevating risk) balanced against attack complexity and the confidentiality and integrity impact being none. Only availability (denial-of-service) is affected. Organizations operating Directory Server under consistent memory pressure or in unpredictable load environments should weight this toward high-priority patching despite the moderate numerical score.

Frequently asked questions