CVE-2017-7765 in Firefox
Summary
by MITRE
The "Mark of the Web" was not correctly saved on Windows when files with very long names were downloaded from the Internet. Without the Mark of the Web data, the security warning that Windows displays before running executables downloaded from the Internet is not shown. Note: This attack only affects Windows operating systems. Other operating systems are unaffected. This vulnerability affects Firefox < 54, Firefox ESR < 52.2, and Thunderbird < 52.2.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2017-7765 represents a critical security flaw in how Windows handles file metadata for executables downloaded from the internet, specifically affecting the "Mark of the Web" feature that serves as a primary defense mechanism against malicious software. This issue stems from Windows' inability to properly store the Mark of the Web data when files with extremely long names are downloaded, effectively bypassing the security warning that should appear before executing such programs. The vulnerability exists at the intersection of file system handling and security policy enforcement, where the operating system fails to maintain the integrity of security metadata that is crucial for user awareness and system protection. The flaw is particularly concerning because it directly undermines the security model that Windows employs to warn users about potentially dangerous downloads from untrusted sources.
The technical implementation of this vulnerability involves the Windows file system's handling of extended path names and the associated security attributes that should be preserved during the download process. When files are downloaded from the internet, Windows automatically sets specific security flags and metadata that trigger the display of security warnings before execution. However, when dealing with files that exceed certain naming length thresholds, the system fails to correctly preserve this metadata, allowing malicious actors to bypass the security measures that would normally prevent automatic execution of downloaded files. This behavior creates a vector for privilege escalation attacks where malware can be executed without user awareness, as the security warning mechanism is effectively disabled. The vulnerability is classified under CWE-119 as a buffer overflow or memory handling issue, specifically related to improper handling of long pathnames and extended file attributes. This technical flaw directly maps to the ATT&CK technique T1059.001 which involves the use of command and scripting interpreters, as attackers can leverage this bypass to execute malicious code without triggering the expected security warnings that would normally alert users to potential threats.
The operational impact of CVE-2017-7765 extends beyond simple bypass of security warnings to create a significant risk for system compromise and data theft. Attackers can exploit this vulnerability by crafting malicious executables with long names and distributing them through phishing campaigns, malicious websites, or compromised software distribution channels. The vulnerability affects not only Windows systems but also impacts browser applications that rely on Windows' security features, specifically affecting Firefox versions before 54, Firefox ESR versions before 52.2, and Thunderbird versions before 52.2. This cross-platform impact occurs because these applications depend on the underlying Windows security model for proper handling of internet downloads, creating a cascading effect where web-based attacks can leverage the Windows vulnerability to compromise systems running these applications. The attack surface is particularly dangerous because it requires minimal user interaction beyond the initial download, and the security warning that should alert users to potential threats is completely suppressed, allowing for silent execution of malicious payloads that can perform various malicious activities including credential theft, system reconnaissance, and installation of additional malware components.
The mitigation strategies for CVE-2017-7765 involve multiple layers of defense that address both the Windows operating system vulnerability and the affected browser applications. System administrators should ensure that all Windows systems are updated to versions that properly handle long file names with security metadata, while also applying patches to Firefox, Firefox ESR, and Thunderbird to prevent exploitation through these applications. The recommended approach includes implementing proper patch management procedures that prioritize security updates, particularly those addressing file system and security attribute handling. Organizations should also consider implementing additional security controls such as application whitelisting, network-based filtering, and behavioral monitoring to detect suspicious activity that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and security attribute preservation in file system operations, and highlights the need for comprehensive testing of security features across different file naming scenarios. Network administrators should monitor for unusual download patterns and ensure that security policies are enforced consistently across all systems, particularly those that interact with internet-based content. This vulnerability serves as a reminder of the critical importance of maintaining up-to-date security patches and the potential for seemingly minor implementation flaws to create significant security risks that can be exploited by attackers.