CVE-2026-11791
Description
A flaw was found in 389 Directory Server. During schema reload, the attr_syntax_swap_ht() function unconditionally frees attribute syntax information nodes, bypassing the refcount-based deferred deletion used elsewhere in the attribute syntax subsystem. If an administrator triggers schema reload while concurrent LDAP query traffic is active, worker threads may access freed memory, resulting in use-after-free or double-free and a denial of service (server crash).
Statement
Red Hat rates this issue as Moderate impact. During schema reload in 389-ds-base, attr_syntax_swap_ht() frees attribute syntax nodes unconditionally, bypassing the refcount-based deferred deletion used elsewhere. An administrator triggering schema reload while concurrent LDAP queries are active can cause use-after-free and crash ns-slapd. Red Hat assigns AC:H and PR:H because the race window is nanoseconds-wide and stress testing did not produce a natural crash; schema reload requires administrative privileges. Schedule schema reloads during maintenance windows with reduced LDAP traffic.
Mitigation
Schedule schema reload operations during maintenance windows with reduced LDAP traffic. Minimize schema reload frequency; in replication topologies schema changes propagate automatically. Monitor for unexpected ns-slapd restarts during or immediately after schema reloads. Restrict write access to cn=schema,cn=config to dedicated administrative accounts via LDAP ACIs.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5 | 5 | 5 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | High | High | High |
| Privileges Required | High | High | High |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | None | None | None |
| Integrity Impact | Low | Low | Low |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:H
NVD: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:H
cve.org: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:H
Red Hat CVSS v3 Score Explanation
AC:H because race window is nanoseconds-wide; stress test (380 reloads + 12 threads, 80s) did not produce natural crash. PR:H because schema reload requires admin privileges. C:N because no info disclosure demonstrated.
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
Acknowledgements
This issue was discovered by Ian Murphy (Red Hat).
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