CVE-2016-5291 in Firefox
Summary
by MITRE
A same-origin policy bypass with local shortcut files to load arbitrary local content from disk. 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
This vulnerability represents a critical security flaw in web browsers that allows attackers to bypass the same-origin policy through the manipulation of local shortcut files. The issue stems from how browsers handle local file references and their interpretation of file paths when processing shortcut files, creating an avenue for unauthorized access to local system resources. The vulnerability specifically impacts Mozilla Firefox and Thunderbird applications, with versions prior to 45.5 ESR and 50 respectively being affected. The same-origin policy is a fundamental security mechanism that restricts how documents or scripts loaded from one origin can interact with resources from another origin, making this bypass particularly concerning for web application security.
The technical implementation of this vulnerability involves exploiting the way browsers process local file shortcuts and their handling of file path resolution. When a browser encounters a local shortcut file, it may inadvertently allow the execution of arbitrary local content that would normally be restricted by security policies. This occurs due to insufficient validation of file paths and improper handling of local resource access, enabling attackers to craft malicious shortcut files that can load and execute local content from the victim's filesystem. The flaw essentially allows for a form of local file inclusion attack where the browser's security boundaries are circumvented through the manipulation of local file references.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the ability to access sensitive local files and potentially execute arbitrary code on the victim's system. This could lead to complete system compromise if attackers can access critical system files, user credentials, or other sensitive data stored locally. The vulnerability is particularly dangerous in environments where users may encounter malicious shortcut files through phishing attacks or compromised websites, as it allows for persistent access to local resources without requiring elevated privileges or additional attack vectors. Security researchers have classified this as a medium to high severity vulnerability due to its potential for privilege escalation and data exfiltration.
Mitigation strategies for this vulnerability include immediate patching of affected browser versions to the latest security releases, which typically involve implementing stricter validation of local file paths and enhancing the same-origin policy enforcement mechanisms. Organizations should also implement security awareness training to educate users about the dangers of opening unknown shortcut files and visiting untrusted websites. Network-level protections such as content filtering and web application firewalls can help detect and block malicious shortcut file attempts. Additionally, browser security configurations should be reviewed to ensure that local file access is restricted to legitimate use cases only, and regular security audits should verify that no unauthorized local file access mechanisms remain active in the browser environment. This vulnerability aligns with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and maps to ATT&CK technique T1059.007 (Command and Scripting Interpreter: JavaScript) as it involves the execution of malicious code through web browser vulnerabilities.