CVE-2026-9064 is a resource exhaustion vulnerability in the get_ldapmessage_controls_ext() function of the 389-ds-base LDAP server used in Red Hat Directory Server. The function does not enforce an upper bound on the number of controls per LDAP message. An attacker can send a crafted LDAP request containing hundreds of thousands of minimal controls within the default 2 MB BER message size, causing excessive CPU usage and heap allocations. Concurrent exploitation can degrade service availability by causing latency, worker thread starvation, or out-of-memory termination, resulting in denial of service. The vulnerability affects Red Hat Directory Server versions 12.2 prior to 12.2.7-15 and 13.2. Mitigations include network access restrictions to LDAP ports and lowering the nsslapd-maxbersize parameter, though only the patch that enforces a maximum controls-per-message limit fully resolves the issue. Red Hat has released an updated container image for version 13.2 containing the fix.

A remote unauthenticated attacker with network access to the LDAP port can cause denial of service by sending a single crafted LDAP request with an excessive number of controls. This leads to unbounded memory allocations and high CPU consumption, resulting in latency degradation, worker thread starvation, or server termination due to out-of-memory conditions. The impact is availability loss of the directory service. There is no impact on confidentiality or integrity.

A patch is available in the updated Red Hat Directory Server 13.2 container image provided by Red Hat. Users should update to this fixed container image by pulling it from the Red Hat container registry. Additionally, network access to LDAP ports (389/tcp and 636/tcp) should be restricted to trusted networks using firewall rules or ACLs to prevent untrusted attackers from reaching the vulnerable code path. Optionally, lowering the nsslapd-maxbersize configuration parameter can reduce the maximum BER message size accepted by the server, partially mitigating the issue, but this does not fully eliminate the amplification and may impact legitimate large LDAP operations.