Heap Buffer Overflow in 389 Directory Server

Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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Executive Summary

CVE-2026-14940 is a heap-buffer-overflow vulnerability in the 389 Directory Server (389-ds-base) that occurs during the normalization of a Distinguished Name (DN). This happens when the DN contains a legacy-quoted value encoding a multivalued nested Relative Distinguished Name (RDN). Specifically, the vulnerability arises because the server improperly handles the closing quote of a nested attribute-value pair, which leads to stale pointers and overlapping data entries.

During the sorting of RDN attribute-value pairs, the server writes past the allocated heap memory, causing a heap-buffer-overflow. An unauthenticated remote attacker can trigger this flaw by sending an LDAP operation, such as a search with a specially crafted base DN, that reaches the DN normalization routine.

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Impact Analysis

This vulnerability can lead to heap memory corruption, which may cause the 389 Directory Server to crash or become unavailable, resulting in a denial of service (DoS).

An unauthenticated remote attacker can exploit this issue, meaning no prior access or credentials are needed to trigger the flaw.

In some environments, the server may simply return an "Invalid DN syntax" error and continue running, but in others, especially with certain memory checking tools enabled, the server process may terminate unexpectedly.

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Detection Guidance

This vulnerability can be detected by attempting to trigger the heap-buffer-overflow condition through LDAP operations that involve DN normalization, such as search operations with a crafted base Distinguished Name (DN) containing legacy-quoted values encoding multivalued nested Relative Distinguished Names (RDN).

In environments with AddressSanitizer (ASAN) or with the environment variable MALLOC_CHECK_=3 set, triggering the vulnerability causes the 389 Directory Server (ns-slapd) process to crash with a general protection fault, which can be used as an indicator.

A practical approach is to perform LDAP search commands with a specially crafted base DN designed to exercise the vulnerable DN normalization routine.

• Use ldapsearch with a crafted base DN that includes legacy-quoted multivalued nested RDNs to test the server's response.
• Set the environment variable MALLOC_CHECK_=3 before starting the 389 Directory Server to detect memory corruption crashes.
• Monitor the ns-slapd process for crashes or general protection faults during these tests.

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Mitigation Strategies

Immediate mitigation steps include updating the 389 Directory Server (389-ds-base) to a version that contains the fix for this heap-buffer-overflow vulnerability.

If an update is not immediately possible, consider restricting or filtering LDAP operations that involve DN normalization, such as limiting or blocking search requests with crafted base DNs from untrusted sources.

Additionally, running the server with memory corruption detection tools enabled (e.g., setting MALLOC_CHECK_=3) can help detect exploitation attempts early by causing the server to crash instead of continuing in a corrupted state.

Monitoring logs and system behavior for unusual LDAP errors or crashes can also help in early detection and response.

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