CVE-2025-65319 is a security vulnerability identified in Blue Mail versions 1.140.103 and earlier, related to the handling of email attachments. Specifically, when users interact with attachments, Blue Mail saves these files to the local file system but fails to apply the Mark-of-the-Web (MOTW) tag. MOTW is a security feature used by Windows OS and many third-party security tools to flag files downloaded from potentially unsafe sources, triggering security warnings or sandboxing behaviors. Without this tag, files saved by Blue Mail are treated as trusted local files, allowing malicious attachments to bypass built-in OS protections such as SmartScreen, Windows Defender Application Guard, and other endpoint security solutions that rely on MOTW to enforce execution policies. This flaw can be exploited by attackers who send malicious attachments via email; once saved, these files can execute or be opened without the usual security prompts, increasing the risk of malware infection or unauthorized code execution. Although no known exploits are currently reported in the wild, the vulnerability poses a significant risk due to the widespread use of Blue Mail in corporate and personal environments. The lack of a CVSS score indicates that the vulnerability is newly published, and no official severity rating has been assigned yet. The vulnerability affects confidentiality and integrity by enabling potentially malicious files to run unchecked, and it does not require complex exploitation techniques or elevated privileges. The absence of patches at the time of publication necessitates immediate attention to alternative mitigations.

For European organizations, this vulnerability can lead to increased risk of malware infections, ransomware attacks, and data breaches. Since Blue Mail is used by various enterprises and individuals for email communication, the ability to bypass OS-level file protections means that malicious attachments could execute without triggering security alerts, compromising endpoint security. This is particularly critical for sectors handling sensitive or regulated data such as finance, healthcare, and government institutions. The vulnerability undermines trust in email as a secure communication channel and could facilitate lateral movement within networks if attackers gain initial footholds via malicious attachments. Additionally, the lack of MOTW tagging may allow attackers to evade detection by security monitoring tools that rely on this metadata. The impact extends to operational disruption, potential data loss, and reputational damage. Organizations with less mature endpoint protection or those relying heavily on Blue Mail are at greater risk. The threat also complicates compliance with European data protection regulations like GDPR, as breaches resulting from this vulnerability could lead to regulatory penalties.

Until an official patch is released, European organizations should implement the following specific mitigations: 1) Enforce strict email attachment policies, including blocking or sandboxing attachments from untrusted sources before delivery to end users. 2) Deploy endpoint protection solutions that do not solely rely on MOTW tagging but use behavior-based detection and real-time scanning to identify malicious files. 3) Educate users on the risks of opening unexpected or suspicious attachments, emphasizing caution even if no security warnings appear. 4) Configure email gateways to scan and quarantine potentially harmful attachments proactively. 5) Consider using alternative email clients with robust attachment handling and security features if Blue Mail usage is widespread. 6) Monitor network and endpoint logs for unusual file execution patterns or unauthorized access attempts. 7) Implement application whitelisting and least privilege principles to limit the impact of any executed malicious files. 8) Regularly update all security software and operating systems to ensure the latest protections are in place. These measures collectively reduce the risk posed by the absence of MOTW tagging and help maintain a strong security posture.