CVE-2026-58218

Samba: dns signing dos via tkey name cache exhaustion

Published Jul 30, 2026 CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed

Description

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.

Analysis

Technical impact

A flaw in Samba’s internal DNS server allows unauthenticated TKEY registration requests to be cached before rejection; a remote attacker can flood the server with many such requests using arbitrary names, causing cache exhaustion that evicts legitimate TKEY entries. The result is that legitimate TSIG authentication for signed DNS queries fails, leading to a denial of service for DNS signing and related services.

Affected Systems

The vulnerability affects Samba running on Red Enterprise Linux 6 through 10 and on Red OpenShift Container Platform 4. No specific Samba version is listed; any installation of Samba on these platforms that supports DNS signing is potentially vulnerable.

Risk and Exploitability

The CVSS score of 5.3 indicates a moderate severity, and the EPSS score of 1% suggests a low but non‑zero exploitation potential. The lack of a KEV listing combined with the remote unauthenticated nature of the attack indicates that the vulnerability is realistic but unlikely to be widely exploited. An attacker would need only network access to the machine’s DNS service to trigger the denial of service by sending a high volume of TKEY requests.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor	Product	Default status	Versions
Red Hat	Red Hat Enterprise Linux 10	unknown	—
Red Hat	Red Hat Enterprise Linux 6	unknown	—
Red Hat	Red Hat Enterprise Linux 6	unknown	—
Red Hat	Red Hat Enterprise Linux 7	unknown	—
Red Hat	Red Hat Enterprise Linux 8	unknown	—
Red Hat	Red Hat Enterprise Linux 9	unknown	—
Red Hat	Red Hat OpenShift Container Platform 4	unknown	—

No data.

Vendor Product Versions

Redhat

Enterprise Linux

Version	Status	Scheme	Platform
`—`	affected	—	—

Redhat

Openshift Container Platform

Version	Status	Scheme	Platform
`—`	affected	—	—

Samba

Version	Status	Scheme	Platform
`—`	affected	—	—

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade Samba to a version that has corrected the cache handling flaw, following the Red Hat security advisory for CVE‑2026‑58218
Configure the TKEY name cache to impose a stricter size limit or disable TKEY usage if it is not required, to prevent excessive memory consumption
Implement network‑layer controls such as DNS firewall rules or rate‑limiting to reduce the impact of large volumes of TKEY requests from untrusted hosts

Generated by OpenCVE AI on August 2, 2026 at 05:21 UTC.

Tracking

Advisories

Source	ID	Title
Debian DSA	DSA-6401-1	samba security update
Ubuntu USN	USN-8621-1	Samba vulnerabilities

Metrics

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact Low

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.784% probability within 30 days)

Exploitation none

Automatable yes

Technical Impact partial

References

Link	Providers
https://access.redhat.com/security/cve/CVE-2026-58218
https://bugzilla.redhat.com/show_bug.cgi?id=2502728
https://bugzilla.samba.org/show_bug.cgi?id=16115
https://nvd.nist.gov/vuln/detail/CVE-2026-58218
https://www.cve.org/CVERecord?id=CVE-2026-58218
https://www.samba.org/samba/security/CVE-2026-58218.html

History

Jul 31, 2026 12:15 AM Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
References		https://nvd.nist.gov/vuln/detail/CVE-2026-58218 https://www.cve.org/CVERecord?id=CVE-2026-58218
Metrics	threat_severity `None`	threat_severity `Moderate`

Jul 30, 2026 8:45 PM First appearance in the feed. Affected vendors updated View changes

Type	Values Removed	Values Added
First Time appeared		Redhat openshift Container Platform Samba Samba samba
Vendors & Products		Redhat openshift Container Platform Samba Samba samba

Jul 30, 2026 6:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Jul 30, 2026 2:15 PM Description updated. Title updated. First appearance in the feed. Weaknesses updated. Affected versions updated. Affected vendors updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
Description		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.
Title		Samba: dns signing dos via tkey name cache exhaustion
First Time appeared		Redhat Redhat enterprise Linux Redhat openshift
Weaknesses		CWE-410
CPEs		cpe:/a:redhat:openshift:4 cpe:/o:redhat:enterprise_linux:10 cpe:/o:redhat:enterprise_linux:6 cpe:/o:redhat:enterprise_linux:7 cpe:/o:redhat:enterprise_linux:8 cpe:/o:redhat:enterprise_linux:9
Vendors & Products		Redhat Redhat enterprise Linux Redhat openshift
References		https://access.redhat.com/security/cve/CVE-2026-58218 https://bugzilla.redhat.com/show_bug.cgi?id=2502728 https://bugzilla.samba.org/show_bug.cgi?id=16115 https://www.samba.org/samba/security/CVE-2026-58218.html
Metrics		cvssV3_1 `{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}`