The BLOCKED access control list items that are evaluated to deny access on the the proxy protocol port can be bypassed completely when connecting over TCP or TLS and sending the query twice on connection that is kept open.

The remote Fedora 45 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-c56ac69334 advisory.

    BUG FIXES:

        Fix for CVE-2026-18664: IP range access control restrictions are bypassed for some unintended IP.
        Thanks to Qifan Zhang, Palo Alto Networks for the report         Thanks to Claude and Ada Logics for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-18664.txt         Fix for CVE-2026-18916: Any remote client can denial TCP service by throttling the TCP receive window     (down to 1).
        Thanks to Akhil Koul (https://github.com/akoul) for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-18916.txt         Fix for CVE-2026-19401: Any remote client can denial UDP service by sending a specifically crafted     query with multiple DNS Cookie options.
        Thanks to Qifan Zhang, Palo Alto Networks for the report         Thanks to afldl zhangph@yandex.com for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19401.txt         Fix for CVE-2026-19538: Anyone with access to the proxy protocol port over TCP or TLS can bypass     BLOCKED access control items.
        Thanks to Qifan Zhang, Palo Alto Networks for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19538.txt


Tenable has extracted the preceding description block directly from the Fedora security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Fedora 43 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-3ff003d397 advisory.

    BUG FIXES:

        Fix for CVE-2026-18664: IP range access control restrictions are bypassed for some unintended IP.
        Thanks to Qifan Zhang, Palo Alto Networks for the report         Thanks to Claude and Ada Logics for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-18664.txt         Fix for CVE-2026-18916: Any remote client can denial TCP service by throttling the TCP receive window     (down to 1).
        Thanks to Akhil Koul (https://github.com/akoul) for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-18916.txt         Fix for CVE-2026-19401: Any remote client can denial UDP service by sending a specifically crafted     query with multiple DNS Cookie options.
        Thanks to Qifan Zhang, Palo Alto Networks for the report         Thanks to afldl zhangph@yandex.com for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19401.txt         Fix for CVE-2026-19538: Anyone with access to the proxy protocol port over TCP or TLS can bypass     BLOCKED access control items.
        Thanks to Qifan Zhang, Palo Alto Networks for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19538.txt


Tenable has extracted the preceding description block directly from the Fedora security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Fedora 44 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-bf1539678e advisory.

    BUG FIXES:

        Fix for CVE-2026-18664: IP range access control restrictions are bypassed for some unintended IP.
        Thanks to Qifan Zhang, Palo Alto Networks for the report         Thanks to Claude and Ada Logics for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-18664.txt         Fix for CVE-2026-18916: Any remote client can denial TCP service by throttling the TCP receive window     (down to 1).
        Thanks to Akhil Koul (https://github.com/akoul) for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-18916.txt         Fix for CVE-2026-19401: Any remote client can denial UDP service by sending a specifically crafted     query with multiple DNS Cookie options.
        Thanks to Qifan Zhang, Palo Alto Networks for the report         Thanks to afldl zhangph@yandex.com for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19401.txt         Fix for CVE-2026-19538: Anyone with access to the proxy protocol port over TCP or TLS can bypass     BLOCKED access control items.
        Thanks to Qifan Zhang, Palo Alto Networks for the report         https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19538.txt


Tenable has extracted the preceding description block directly from the Fedora security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of FreeBSD installed on the remote host is prior to tested version. It is, therefore, affected by multiple vulnerabilities as referenced in the a711b018-a24b-11f1-81e6-3c7c3fba4204 advisory.

    NLnet Labs reports:

Tenable has extracted the preceding description block directly from the FreeBSD security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - The BLOCKED access control list items that are evaluated to deny access on the the proxy protocol port can     be bypassed completely when connecting over TCP or TLS and sending the query twice on connection that is     kept open. (CVE-2026-19538)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
344863	Fedora 45 : nsd (2026-c56ac69334)	Nessus	Fedora Local Security Checks	Local	high
343792	Fedora 43 : nsd (2026-3ff003d397)	Nessus	Fedora Local Security Checks	Local	high
343782	Fedora 44 : nsd (2026-bf1539678e)	Nessus	Fedora Local Security Checks	Local	high
341545	FreeBSD : NSD -- multiple vulnerabilities (a711b018-a24b-11f1-81e6-3c7c3fba4204)	Nessus	FreeBSD Local Security Checks	Local	high
341350	Linux Distros Unpatched Vulnerability : CVE-2026-19538	Nessus	Misc.	Local	high

Detections

Analytics

CVE-2026-19538

high

Tenable Plugins

high

high

high

high

high