CVE-2026-11791

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).

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.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

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.