.NET WPF EUVD-2026-100204

Exploitation requires the victim to open or render attacker-controlled XAML/XPS markup in a WPF application built on an affected Microsoft.WindowsDesktop.App.Runtime version (Windows only; all architectures). The specific weakness is permissive input allow-listing (CWE-183) in WPF's URI fetching, hyperlink navigation, and DNS zone-policy handling - the fix adds restrictive URI/navigation blocking, untrusted-input state propagation through hyperlinks, TrueType font protection, XAML nesting-depth limits, and stops caching positive DNS zone-policy decisions. Limiting factors: mandatory user interaction (UI:R - the app must load untrusted content), confinement to Windows desktop WPF workloads (server/console/web .NET apps without WindowsDesktop runtime are not affected), and impact limited to confidentiality (no integrity or availability loss). Exploitation is not automatable per SSVC.

This is a moderate-severity information disclosure flaw (CVSS 6.5, CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N) in the WPF component of .NET (Microsoft.WindowsDesktop.App.Runtime). The signals are internally consistent and point to a lower real-world priority than the 'network, unauthenticated' vector alone might suggest. The CVSS confidentiality impact is High (C:H) but requires user interaction (UI:R) - a victim must open attacker-supplied XAML/XPS content - which materially limits mass exploitation. The SSVC decision framework reinforces this: Exploitation=none, Automatable=no, Technical Impact=partial, which aligns with CISA's 'Track' rather than 'Act' outcome. There is no CISA KEV listing and no public exploit identified, and no EPSS score was provided in the input (EPSS data missing - cannot quantify exploitation probability). Microsoft rates it Moderate. The dominant limiting factor is the required user interaction plus the Windows-desktop-only WPF attack surface; integrity and availability are unaffected (I:N/A:N). Bottom line: a legitimate patch-management item, not an emergency - prioritize behind internet-facing, automatable, or actively-exploited issues.

An attacker crafts a malicious XAML or XPS document (or a WPF application loading untrusted markup) that abuses permissive URI/DNS handling to fetch or leak data when rendered. A victim running a vulnerable WPF application opens the attacker-supplied content, causing the application to resolve attacker-controlled URIs or hyperlink navigation and disclose sensitive information over the network. No public exploit identified at time of analysis, and user interaction is required for the attack to succeed.