CVE-2026-96222

Improper certificate validation in Active Directory Federation Services (AD FS) allows an unauthorized attacker to perform spoofing over a network.

An improper certificate validation flaw of IMPORTANT severity was found in the .NET System.Security.Cryptography.Xml library as shipped in the dotnet8.0 packages of Red Hat Enterprise Linux 8, 9, and 10, Red Hat In-Vehicle OS, and Red Hat Hardened Images. The KeyInfoX509Data API can accept serialized certificate formats containing attacker-controlled chain metadata instead of requiring a plain X.509 certificate, enabling certificate-forgery and token-spoofing paths. A remote, unauthenticated attacker could exploit this weakness, which Microsoft describes as a spoofing vulnerability in Active Directory Federation Services (AD FS), to forge certificates and spoof signed content or tokens, compromising the confidentiality and integrity of certificate and token validation. Exploitation requires high attack complexity, and the Red Hat CVSS 3.1 score of 7.4 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N) matches the upstream assessment. Fixes for the affected Red Hat products are delegated to the upstream .NET correction, which is being pursued for all affected streams.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.