CVE-2026-58218

A flaw was found in Samba's internal DNS server where unauthenticated TKEY registration requests were added to the TKEY name cache before being rejected. A remote, unauthenticated attacker can exploit this behavior by sending a large number of TKEY requests with arbitrary names, exhausting the cache and evicting legitimate TKEY entries. This can prevent legitimate TSIG authentication for signed DNS queries, resulting in a denial of service.

Red Hat Product Security has rated this vulnerability as having a Moderate security impact for Samba deployments operating as an Active Directory Domain Controller (AD DC) using the internal DNS server.

Red Hat Enterprise Linux (RHEL) context: Standard Red Hat Enterprise Linux deployments are not affected. RHEL does not support the Samba Active Directory Domain Controller (AD DC) role or its internal DNS server, where this vulnerability resides.

Additionally, Samba AD DC deployments configured to use the external BIND9 DLZ backend instead of the internal DNS server are not affected by this vulnerability.

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.