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).
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.