Executive Summary

CVE-2026-11884 is a heap buffer overflow vulnerability in the 389 Directory Server related to how objectclass definitions are serialized. Specifically, the length of the oc_superior (SUP) field is not included in buffer size calculations in the functions read_schema_dse() and schema_oc_to_string(), but the SUP field is still written using strcat(). This mismatch can cause a buffer overflow.

There are two variants of this vulnerability: one triggers an overflow when the SUP field is about 248 bytes or larger during schema DSE reads, and the other triggers an overflow when the SUP field is about 62 bytes or larger during schema replication comparison.

An attacker with Directory Manager privileges or a compromised replication supplier can exploit this flaw to crash the server. However, remote code execution is not feasible on x86_64 systems due to the ASCII-only nature of the overflow content.

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Impact Analysis

This vulnerability can be exploited to cause a denial of service by crashing the 389 Directory Server. An attacker with Directory Manager privileges or a compromised replication supplier can trigger this crash by creating objectclasses with long SUP values.

In replication environments, a compromised supplier could push malicious schema data to consumers, causing them to crash as well.

While remote code execution is not feasible on x86_64 systems due to the nature of the overflow, the server crash can disrupt directory services, potentially impacting availability and operations.

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Detection Guidance

This vulnerability involves a heap buffer overflow in the 389 Directory Server related to the oc_superior (SUP) field length during schema objectclass serialization. Detection would involve checking for unusually long SUP field values in objectclass definitions, especially those around or exceeding 62 bytes or 248 bytes depending on the function variant.

Since the vulnerability can be triggered by creating objectclasses with long SUP values, detection commands could include querying the directory server schema for objectclasses with SUP fields longer than these thresholds.

• Use ldapsearch or similar LDAP query tools to retrieve objectclass definitions and inspect the length of the oc_superior attribute.
• Example command to list objectclasses and their SUP fields: ldapsearch -x -b cn=schema -s base objectClasses
• Parse the output to identify any SUP fields with lengths near or exceeding 62 or 248 characters.

Additionally, monitoring server logs for crashes or abnormal terminations related to schema operations could help detect exploitation attempts.

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Mitigation Strategies

Immediate mitigation steps include applying the official patch or update provided by the vendor to fix the heap buffer overflow in the 389 Directory Server.

Until a patch is applied, restrict Directory Manager privileges to trusted administrators only, as exploitation requires such privileges.

In replication topologies, ensure that replication suppliers are secure and trusted to prevent malicious schema pushes.

Monitor the server for crashes or unusual behavior that might indicate exploitation attempts.

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Compliance Impact

The provided information does not specify any direct impact of CVE-2026-11884 on compliance with common standards and regulations such as GDPR or HIPAA.

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