Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.

An update of the dotnet package has been released.

The remote Ubuntu 22.04 LTS / 25.10 host has packages installed that are affected by a vulnerability as referenced in the USN-8025-1 advisory.

    Kevin Jones discovered that the System.Security.Cryptography.Cose component in .NET did not properly     handle certain missing special elements in input data. An attacker could possibly use this issue to bypass     security checks and gain unauthorized access or perform data manipulation.

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

Note that Nessus has not tested for this issue 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.

  - Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing     over a network. (CVE-2026-21218)

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

The version of tested product installed on the remote host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the vendor advisory.

  - .NET Spoofing Vulnerability (CVE-2026-21218)

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

ID	Name	Product	Family	Severity
300527	Photon OS 5.0: Dotnet PHSA-2026-5.0-0778	Nessus	PhotonOS Local Security Checks	high
298898	Ubuntu 22.04 LTS / 25.10 : .NET vulnerability (USN-8025-1)	Nessus	Ubuntu Local Security Checks	high
298781	Linux Distros Unpatched Vulnerability : CVE-2026-21218	Nessus	Misc.	high
298547	Security Update for Microsoft .NET Core (February 2026)	Nessus	Windows	high

Detections

Analytics

CVE-2026-21218

high

Tenable Plugins

high

high

high

high