CVE-2026-109782 in Firefox
Summary
by MITRE • 10/13/2026
Mitigation bypass in the File Handling component. This vulnerability was fixed in Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/13/2026
The identified security issue represents a critical failure within the file handling subsystem of Mozilla Firefox Extended Support Release version 153.4 and earlier, specifically categorized as a mitigation bypass. In modern web browsers, mitigations such as Content Security Policy (CSP), Same-Origin Policy (SOP), and various sandboxing mechanisms are designed to restrict how content interacts with local resources or other origins. A vulnerability in this domain implies that an attacker was able to circumvent these protective controls through the file handling logic, potentially allowing unauthorized access to sensitive data or execution of malicious scripts under elevated privileges. This type of flaw is particularly dangerous because it undermines the foundational trust model of the browser environment, where users expect isolation between web content and local system resources.
From a technical perspective, vulnerabilities in file handling components often stem from improper validation of input paths, race conditions during file operations, or incorrect interpretation of security headers when processing downloaded files. The specific nature of this bypass suggests that the application failed to enforce restrictions intended by its own security policies when interacting with the operating system's file API. This could involve scenarios where a malicious webpage triggers a download or access request that exploits edge cases in how Firefox processes local file URIs, thereby escaping the expected sandbox boundaries. Such flaws are frequently associated with CWE-20 Improper Input Validation and CWE-798 Use of Hard-coded Credentials if authentication tokens were improperly handled during the bypass process.
The operational impact of this vulnerability is significant for users who rely on Firefox ESR for enterprise or institutional environments where strict security compliance is mandatory. An attacker could potentially use a crafted web page to read sensitive files from the user's local filesystem, exfiltrate data without detection, or execute arbitrary code by leveraging the elevated permissions gained through the bypassed mitigation. This compromises both confidentiality and integrity of user data. The risk is exacerbated in environments where browsers are used for accessing internal corporate resources, as a successful exploit could serve as an initial foothold for further lateral movement within a network if combined with other attack vectors like phishing or drive-by downloads.
To address this issue, users must upgrade to Firefox ESR version 153.5 immediately, as the vendor has released patches that correct the logic errors in the file handling component. Organizations should ensure their patch management systems are configured to prioritize security updates for browser components due to the high prevalence of exploitation techniques targeting these areas. Additionally, administrators can enforce stricter Content Security Policies via group policy settings to limit script execution and resource loading from untrusted sources, providing an additional layer of defense even if similar vulnerabilities arise in future versions. Regular auditing of installed extensions is also recommended, as malicious add-ons could potentially exploit such weaknesses more easily than standard web content due to their elevated permissions within the browser environment.