EUVD-2026-51128
GHSA-qcxx-8h4x-9v7w
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Network-reachable DNS port, no authentication or complexity required; impact is limited availability loss (TSIG cache only), with no confidentiality or integrity effect.
Primary rating from Vendor (redhat).
CVSS VectorVendor: redhat
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Lifecycle Timeline
2DescriptionCVE.org
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.
AnalysisAI
Samba's internal DNS server inserts unauthenticated TKEY registration requests into the TKEY name cache before rejecting them, allowing a remote unauthenticated attacker to exhaust the cache by flooding it with arbitrary TKEY names. Eviction of legitimate cache entries blocks TSIG-authenticated DNS query processing, producing a targeted denial of service against Active Directory environments relying on Samba's built-in DNS backend. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the targeted Samba instance is configured to use Samba's internal DNS server backend (the default for Samba AD DC deployments; not applicable when BIND or an external DNS is used as the AD DNS backend). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 base score of 5.3 (Medium) reflects a purely network-delivered, unauthenticated, zero-complexity attack with only limited availability impact - consistent with a resource exhaustion DoS rather than code execution. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An unauthenticated attacker on the network sends a high-rate stream of DNS TKEY requests carrying arbitrary, unique names to Samba's DNS listener on port 53. Each request is inserted into the finite TKEY name cache before Samba's validation logic rejects it, causing the cache to fill with attacker-controlled junk entries that displace legitimate TKEY state. … |
| Remediation | Apply the vendor-released patch from Samba upstream (https://www.samba.org/samba/security/CVE-2026-58218.html) or via your Linux distribution's package manager - Red Hat advisory at https://access.redhat.com/security/cve/CVE-2026-58218, Ubuntu at https://ubuntu.com/security/notices/USN-8621-1. … Detailed patch versions, workarounds, and compensating controls in full report. |
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