CVE-2025-66631 is a deserialization vulnerability classified under CWE-502 affecting the CSLA .NET framework, a widely used framework for building reusable, object-oriented business layers in applications. The vulnerability exists in versions 5.5.4 and earlier, specifically within the WcfProxy component that utilizes the deprecated NetDataContractSerializer (NDCS). NDCS is known to be unsafe because it deserializes data without sufficient validation, allowing attackers to craft malicious serialized payloads that, when deserialized, can execute arbitrary code remotely. This vulnerability does not require authentication or user interaction, making it remotely exploitable over the network. The CVSS 4.0 base score is 7.2, indicating high severity, with network attack vector, low attack complexity, and no privileges required. The vulnerability impacts confidentiality, integrity, and availability by enabling remote code execution, potentially leading to full system compromise. The issue is resolved in CSLA .NET version 6.0.0, which removes or replaces the vulnerable serialization mechanism. As an immediate workaround, organizations can disable or remove the WcfProxy component from their data portal configurations to prevent exposure. No public exploits have been reported yet, but the vulnerability's nature and ease of exploitation make it a critical concern for developers and system administrators using affected versions.

For European organizations, the impact of CVE-2025-66631 can be severe, especially those relying on CSLA .NET for critical business applications. Successful exploitation allows attackers to execute arbitrary code remotely, potentially leading to data breaches, system downtime, and unauthorized access to sensitive business logic and data. This can disrupt operations, cause financial losses, and damage reputations. Given the framework’s use in enterprise environments, attackers could pivot within networks to escalate privileges or move laterally. The vulnerability affects confidentiality, integrity, and availability, making it a comprehensive threat. Organizations in sectors such as finance, manufacturing, and government, which often use .NET frameworks for internal applications, are particularly vulnerable. The lack of required authentication and user interaction increases the risk of automated or widespread attacks. Although no known exploits are currently in the wild, the vulnerability’s characteristics suggest that exploitation could become common once public proof-of-concept code appears.

1. Upgrade CSLA .NET to version 6.0.0 or later immediately, as this version contains the official fix for the vulnerability. 2. If immediate upgrade is not feasible, remove or disable the WcfProxy component in the data portal configurations to prevent the vulnerable serialization mechanism from being used. 3. Review and restrict network access to services using CSLA .NET, especially those exposing WcfProxy endpoints, limiting exposure to trusted internal networks only. 4. Implement application-layer firewalls or intrusion detection systems to monitor and block suspicious serialized payloads targeting the vulnerable component. 5. Conduct thorough code audits to identify any custom deserialization logic that might be vulnerable and refactor to use safe serialization alternatives. 6. Educate developers and system administrators about the risks of unsafe deserialization and encourage adoption of secure coding practices. 7. Monitor vendor advisories and threat intelligence feeds for any emerging exploits or patches related to this vulnerability.