CVE-2026-58218
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.
Statement
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.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.3 | N/A | 5.3 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | Low | N/A | Low |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Understanding the Weakness (CWE)
Availability,Integrity,Other
Technical Impact: DoS: Crash, Exit, or Restart; Other
Floods often cause a crash or other problem besides denial of the resource itself; these are likely examples of *other* vulnerabilities, not an insufficient resource pool.
Acknowledgements
Red Hat would like to thank Andrew Tridgell (Samba Team) and Tristan Madani (Talence Security) for reporting this issue.
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