CVE-2025-6811 is a critical remote code execution vulnerability found in Mescius ActiveReports.NET version 18.1.1, specifically within the TypeResolutionService class. This vulnerability arises from improper validation of user-supplied data during deserialization, classified under CWE-502 (Deserialization of Untrusted Data). When an application using this library processes serialized data without adequate checks, an attacker can craft malicious serialized objects that, upon deserialization, execute arbitrary code within the context of the affected process. The vulnerability requires interaction with the ActiveReports.NET library, meaning exploitation depends on how the library is integrated and used in the target environment. The CVSS v3.0 score of 9.8 reflects the vulnerability's high severity, with network attack vector, no privileges or user interaction required, and full impact on confidentiality, integrity, and availability. Although no public exploits have been reported yet, the critical nature and ease of exploitation make it a significant threat. ActiveReports.NET is a reporting tool commonly used in .NET applications to generate reports, so any application leveraging this component and processing untrusted serialized data is at risk. The lack of a patch link suggests that a fix may not yet be publicly available, increasing urgency for mitigation.

For European organizations, this vulnerability poses a severe risk, especially those relying on Mescius ActiveReports.NET in their software stack. Successful exploitation can lead to full system compromise, allowing attackers to execute arbitrary code remotely without authentication or user interaction. This can result in data breaches, disruption of business operations, and potential lateral movement within corporate networks. Organizations in sectors such as finance, healthcare, government, and critical infrastructure, which often use .NET-based reporting tools, could face significant operational and reputational damage. The vulnerability's ability to compromise confidentiality, integrity, and availability simultaneously amplifies its impact. Additionally, given the remote exploitability and lack of required privileges, automated attacks or worm-like propagation could be possible if attackers develop exploits, increasing the threat landscape for European enterprises.

Immediate mitigation steps should include: 1) Conducting an inventory to identify all applications and services using Mescius ActiveReports.NET version 18.1.1. 2) Applying any available patches or updates from Mescius as soon as they are released. 3) If patches are not yet available, consider temporarily disabling or isolating services that utilize the vulnerable component, especially those exposed to untrusted networks or users. 4) Implement strict input validation and sanitization on all serialized data inputs to prevent untrusted data deserialization. 5) Employ application-layer firewalls or intrusion prevention systems to monitor and block suspicious serialized payloads targeting the TypeResolutionService. 6) Review and harden application permissions to limit the impact of potential code execution. 7) Monitor logs and network traffic for unusual activity indicative of exploitation attempts. 8) Engage with software vendors and security communities for updates and exploit intelligence. These measures go beyond generic advice by focusing on the specific vulnerable component and its integration context.