CVE-2017-7767 in Firefox
Summary
by MITRE
The Mozilla Maintenance Service can be invoked by an unprivileged user to overwrite arbitrary files with junk data using the Mozilla Windows Updater, which runs with the Maintenance Service's privileged access. Note: This attack requires local system access and only affects Windows. Other operating systems are not affected. This vulnerability affects Firefox ESR < 52.2 and Firefox < 54.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability described in CVE-2017-7767 represents a critical privilege escalation flaw within the Mozilla Maintenance Service on Windows operating systems. This issue stems from improper access control mechanisms that allow unprivileged local users to manipulate the update process and potentially overwrite arbitrary files with malicious data. The flaw specifically exploits the interaction between the Mozilla Windows Updater and the Maintenance Service, which operates with elevated privileges. The vulnerability exists due to insufficient validation of file operations performed during the update process, creating a path for malicious file manipulation that bypasses normal security boundaries.
The technical implementation of this vulnerability involves the exploitation of the Windows Updater component that communicates with the Maintenance Service through a privileged execution context. When the update process is initiated, the system fails to properly validate or sanitize file paths that are being modified during the update procedure. This allows a local attacker with standard user privileges to craft specific inputs or manipulate the update process in such a way that the Maintenance Service, which runs with elevated permissions, performs destructive file operations on behalf of the unprivileged user. The attack vector specifically leverages the trust relationship between the updater and the maintenance service, where the maintenance service executes with higher privileges than the user initiating the update process.
The operational impact of this vulnerability extends beyond simple file corruption, as it provides an attacker with the capability to overwrite critical system files or user data with junk data, potentially leading to system instability or complete system compromise. The vulnerability affects specific versions of Firefox ESR and Firefox, making it particularly concerning for organizations running older versions of these browsers. The requirement for local system access means that while the attack cannot be performed remotely, it represents a significant risk in environments where local access is possible, such as shared workstations or systems with compromised user accounts. This vulnerability directly impacts the principle of least privilege, as it allows a user to escalate their privileges through legitimate system update mechanisms.
Mitigation strategies for this vulnerability require immediate patching of affected Firefox versions to ensure proper privilege separation and access control validation. Organizations should implement strict access controls and monitor for unauthorized file modifications, particularly in system directories where the maintenance service operates. The fix involves proper input validation and sanitization of file paths within the update process, ensuring that the Maintenance Service does not perform operations that could be influenced by unprivileged users. Additionally, system administrators should consider implementing application whitelisting policies and monitoring for suspicious update activities. This vulnerability aligns with CWE-276, which addresses improper privilege management, and represents a clear violation of the principle of least privilege. From an ATT&CK perspective, this vulnerability maps to privilege escalation techniques and could be leveraged as part of broader attack chains targeting system integrity and persistence mechanisms.