CVE-2016-5294 in Firefox
Summary
by MITRE
The Mozilla Updater can be made to choose an arbitrary target working directory for output files resulting from the update process. This vulnerability requires local system access. Note: this issue only affects Windows operating systems. This vulnerability affects Thunderbird < 45.5, Firefox ESR < 45.5, and Firefox < 50.
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Analysis
by VulDB Data Team • 11/25/2025
The vulnerability identified as CVE-2016-5294 represents a critical directory traversal flaw within Mozilla's updater component that specifically impacts Windows operating systems. This issue stems from improper handling of working directory selection during the software update process, allowing an attacker with local system access to manipulate where update files are written. The flaw exists in the Mozilla updater mechanism that manages the installation of security patches and feature updates for various Mozilla products including Firefox, Thunderbird, and Firefox ESR. The vulnerability's impact is particularly concerning because it occurs during the update process when the system is already in a state of trust, making it an attractive target for privilege escalation attacks. This weakness is classified under CWE-22 as Improper Limitation of a Pathname to a Restricted Directory, which directly relates to path traversal vulnerabilities. The issue manifests specifically on Windows platforms where the updater component lacks proper validation of directory paths, potentially allowing malicious actors to write files to arbitrary locations on the system.
The technical exploitation of this vulnerability requires an attacker to already possess local system access, which aligns with the ATT&CK technique T1059.1001 for Command and Scripting Interpreter. However, once local access is achieved, the attacker can manipulate the updater to write malicious files to critical system directories, potentially leading to privilege escalation or persistent backdoor installation. The flaw occurs in the update process where the system's working directory is not properly validated or restricted, allowing the updater to accept and process paths that could lead to sensitive locations such as system directories, registry locations, or other critical file systems. This vulnerability affects a broad range of Mozilla products including Thunderbird versions prior to 45.5, Firefox ESR versions prior to 45.5, and standard Firefox versions prior to 50. The updater component's failure to implement proper path validation creates an attack surface that could be leveraged for code execution, data manipulation, or system compromise. The vulnerability's Windows-only nature indicates that the specific implementation of file path handling differs between operating systems, with the Windows version containing the flawed logic that permits arbitrary directory selection.
The operational impact of CVE-2016-5294 extends beyond simple file placement as it creates opportunities for more sophisticated attacks within the update ecosystem. When the updater processes files to locations specified by an attacker, it opens possibilities for DLL injection, file replacement attacks, or privilege escalation through manipulation of system-critical files. The vulnerability essentially allows an attacker to subvert the normal update process by redirecting output to locations where they can gain persistence or execute malicious code. This represents a significant concern for enterprise environments where users may have local access to systems but not necessarily administrative privileges, as the vulnerability could enable a local user to escalate privileges and gain unauthorized access to system resources. The attack vector is particularly dangerous because it exploits the trust relationship between the operating system and the update mechanism, allowing malicious code to be installed or modified in locations that are typically protected from user modification. Organizations using affected Mozilla products face potential exposure to attackers who might use this vulnerability to establish persistent access to systems, modify critical browser functionality, or redirect user traffic through malicious proxy configurations. The vulnerability's impact is amplified by the fact that it affects long-term support releases and mainstream browser versions, meaning that a large number of systems could be potentially compromised. Security teams must consider this vulnerability as part of their broader threat landscape, particularly when evaluating local privilege escalation risks and supply chain attack vectors that could leverage compromised update processes.