Medium [CVE-2026-58218] DNS signing DoS via TKEY name cache exhaustion
This medium-severity Red Hat Linux advisory covers CVE-2026-58218.
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Summary
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. Red Hat severity: Moderate — CVSS 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L).
Weakness: CWE-410. Red Hat lists Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9; Red Hat OpenShift Container Platform 4 as not affected.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · medium-confidence parse· fetched 23 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists. Confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 23 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That does not mean no fix exists. Read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 23 days ago·verify at source
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