CVE-2025-65319 is a critical security vulnerability identified in Blue Mail versions 1.140.103 and earlier. The flaw arises from the application's failure to apply the Mark-of-the-Web (MOTW) tag to documents saved via its attachment interaction functionality. MOTW is a security feature used by Windows OS and many third-party security solutions to mark files downloaded from potentially unsafe sources, enabling enforcement of security policies such as Protected View in Microsoft Office or blocking execution of untrusted files. Without MOTW, files saved by Blue Mail are treated as fully trusted, allowing malicious documents to bypass these built-in protections. The vulnerability has a CVSS v3.1 base score of 9.1, reflecting its critical severity. It requires no privileges or user interaction to exploit, and the attacker can remotely deliver malicious attachments that, once saved, evade security controls. This can lead to unauthorized disclosure or modification of data, severely impacting confidentiality and integrity. While no public exploits have been reported yet, the absence of patches and the critical nature of the vulnerability make it a significant risk. The CWE-693 classification indicates improper control of file attributes or metadata, which in this case compromises the security boundary enforced by the operating system and security tools. Organizations relying on Blue Mail for email communications should be aware of this risk and prepare to implement mitigations.

For European organizations, this vulnerability poses a substantial risk to data confidentiality and integrity, particularly for sectors handling sensitive or regulated information such as finance, healthcare, and government. The bypass of MOTW protections means that malicious attachments can execute or be opened without triggering security warnings or sandboxing, increasing the likelihood of successful malware infections or data breaches. This could lead to unauthorized access to confidential communications, intellectual property theft, or disruption of business operations. The lack of required privileges or user interaction lowers the barrier for attackers, potentially enabling widespread exploitation. Organizations using Blue Mail as a primary email client or in environments with lax endpoint controls are especially vulnerable. The impact is amplified in countries with strict data protection regulations like GDPR, where breaches can result in heavy fines and reputational damage. Additionally, the vulnerability could be leveraged in targeted attacks against high-value European entities, including critical infrastructure and governmental bodies.

Until an official patch is released, European organizations should implement several specific mitigations: 1) Restrict or temporarily disable the use of Blue Mail for handling sensitive attachments, especially in high-risk environments. 2) Enforce strict endpoint security policies that include scanning all email attachments with advanced threat protection tools before saving or opening. 3) Educate users to avoid opening attachments from untrusted sources and to report suspicious emails promptly. 4) Deploy application whitelisting and sandboxing solutions that do not solely rely on MOTW for file trust decisions. 5) Monitor file system activity for unusual creation or modification of documents without MOTW tags. 6) Consider alternative email clients with robust security controls until Blue Mail releases a fix. 7) Collaborate with IT and security teams to implement network-level controls that can detect and block malicious payloads delivered via email. These targeted actions go beyond generic advice by focusing on compensating controls specific to the MOTW bypass nature of this vulnerability.