CVE-2017-5454 in Firefox
Summary
by MITRE
A mechanism to bypass file system access protections in the sandbox to use the file picker to access different files than those selected in the file picker through the use of relative paths. This allows for read only access to the local file system. This vulnerability affects Thunderbird < 52.1, Firefox ESR < 52.1, and Firefox < 53.
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Analysis
by VulDB Data Team • 11/26/2025
This vulnerability represents a critical sandbox escape mechanism that undermines fundamental security boundaries within Mozilla's browser and email client implementations. The flaw resides in how the file picker component handles relative path resolution, creating an unexpected pathway for unauthorized file system access. Attackers can manipulate the file selection process to traverse beyond intended directories and access arbitrary files on the local system, effectively bypassing the intended sandbox restrictions that isolate web content from the underlying operating system.
The technical implementation of this vulnerability exploits the interaction between the file picker UI component and the underlying file system access controls. When users interact with file selection dialogs, the system should enforce strict boundaries around which files can be accessed. However, the vulnerability allows for manipulation of relative path references that can traverse parent directories and access files outside the originally selected scope. This occurs because the application fails to properly validate or sanitize path components before resolving them against the file system. The flaw specifically affects the sandboxing mechanisms that are designed to prevent web content from accessing local files without explicit user consent, creating a dangerous bypass that can be exploited by malicious actors.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables unauthorized read access to sensitive local files including configuration data, personal documents, and potentially system files. Attackers could leverage this to harvest credentials stored in configuration files, access personal data, or gather intelligence about the victim's system environment. The vulnerability affects a wide range of Mozilla products including Thunderbird email client and Firefox browsers, with versions prior to 52.1 for ESR releases and 53 for standard releases. This widespread impact makes it particularly dangerous as it affects both enterprise and individual users who rely on these applications for daily operations, potentially exposing sensitive corporate data or personal information.
Security researchers have classified this vulnerability as a sandbox escape that aligns with common attack patterns documented in the attack framework, where adversaries seek to break out of restricted execution environments to gain broader system access. The vulnerability demonstrates the complexity of implementing secure file access controls in modern web applications, where seemingly innocuous UI components can become attack vectors when proper input validation and access control mechanisms are not properly implemented. Organizations should prioritize immediate patching of affected systems and implement additional monitoring to detect potential exploitation attempts. The fix typically involves strengthening path validation routines and ensuring that relative path resolution respects the intended file picker boundaries, preventing traversal beyond the specified directory scope.
This vulnerability serves as a reminder of the importance of comprehensive security testing for UI components that interact with the file system, particularly those that are designed to provide controlled access to local resources. The attack vector demonstrates how sandboxing mechanisms can be circumvented through subtle implementation flaws in path handling, highlighting the need for defense-in-depth approaches that include multiple layers of access control validation. Security teams should consider implementing additional monitoring for unusual file access patterns and ensure that all file system interactions are properly audited and validated against expected access patterns. The vulnerability also underscores the critical importance of timely patch management for widely used applications like Mozilla Firefox and Thunderbird, where security flaws can have widespread impact across numerous user bases and organizations.