CVE-2026-11884: 389 Directory Server Heap Buffer Overflow in Schema Serialization

Technical summary

CVE-2026-11884 is a heap buffer overflow in 389 Directory Server's schema serialization logic. The vulnerable functions read_schema_dse() and schema_oc_to_string() fail to include the oc_superior (SUP) field length in buffer size calculations, yet the field is still written into the buffer via strcat(). An attacker with Directory Manager privileges or control of a replication supplier can craft objectclass definitions with abnormally long SUP values to trigger heap corruption and denial of service. The vulnerability represents an incomplete remediation of CVE-2025-14905.

Business impact

Directory Server outages disrupt authentication and authorization for dependent applications. An internal attacker or compromised replication partner can force repeated crashes, degrading or disabling LDAP services that many enterprises rely on for identity management. Recovery requires manual intervention and restart, extending downtime. For organizations using 389 DS as their primary directory backbone, this creates a material availability risk.

Affected systems

389 Directory Server is vulnerable. Affected versions have not been disclosed in available advisories; verify the exact affected version range and patched releases directly with Red Hat's security advisory for this CVE. Replication topologies are at higher risk because a compromised or malicious replication supplier can inject the malicious schema without needing local Directory Manager credentials.

Exploitability

Exploitation requires either Directory Manager-level credentials within the same directory, or compromise of a replication supplier system. Network access to the LDAP port (typically 389/636) is necessary, but the CVSS vector reflects that no user interaction is required once the attacker has the needed privilege level. The attack is straightforward: create an objectclass with an oversized SUP field and trigger schema serialization. No sophisticated exploitation technique is needed.

Remediation

Apply the security patch released by Red Hat for 389 Directory Server that addresses CVE-2026-11884. The patch corrects buffer size calculations in schema serialization to account for all fields, including oc_superior. Additionally, restrict Directory Manager account access to trusted administrators and audit replication supplier configurations to detect unauthorized or compromised peers.

Patch guidance

Obtain and deploy the patched version of 389 Directory Server from Red Hat's official repositories. Verify the patch version against the official CVE advisory before deployment. Test the update in a non-production environment first to ensure compatibility with your replication topology and dependent services. Restart the affected Directory Server instances after patching. Monitor for any schema-related errors in logs post-deployment.

Detection guidance

Monitor 389 Directory Server logs for unexpected schema modification attempts, particularly those involving objectclass creation with unusually long attribute values. Watch for unscheduled service restarts or crashes correlated with LDAP replication events or administrative tool usage. Heap buffer overflow patterns may appear as segmentation faults in server logs or core dumps. Network-based detection is limited; focus on log analysis and access controls to identify suspicious Directory Manager activity or replication anomalies.

Why prioritize this

Although scored MEDIUM (6.5), this vulnerability warrants prompt attention because it enables denial of service in a critical identity service. The attack surface is narrow—requiring high privilege or replication compromise—but the impact (service unavailability) is significant. Organizations should prioritize patching after addressing CRITICAL and HIGH vulnerabilities, but well ahead of lower-severity issues.

Risk score, explained

The CVSS 3.1 score of 6.5 (MEDIUM) reflects the requirement for elevated privileges (PR:H) to exploit the flaw and the absence of confidentiality impact (C:N). However, integrity and availability are both affected (I:H/A:H), as the attacker can corrupt memory and crash the service. The network attack vector (AV:N) and low attack complexity (AC:L) keep the score from being lower, but high privilege requirement prevents a higher rating. The score appropriately balances the operational severity against the narrow attack surface.

Frequently asked questions