CVE-2018-5137 in Firefox
Summary
by MITRE
A legacy extension's non-contentaccessible, defined resources can be loaded by an arbitrary web page through script. This script does this by using a maliciously crafted path string to reference the resources. Note: this vulnerability does not affect WebExtensions. This vulnerability affects Firefox < 59.
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Analysis
by VulDB Data Team • 02/05/2021
This vulnerability represents a critical security flaw in Firefox's legacy extension system that allows arbitrary web pages to load resources from legacy extensions through crafted script paths. The issue stems from how Firefox handles resource loading in its older extension framework, where certain non-content-accessible resources could be inadvertently exposed to web pages. The vulnerability specifically affects Firefox versions prior to 59, making it a significant concern for users running outdated browsers. This represents a privilege escalation risk where malicious websites can access extension resources that should remain isolated from web content.
The technical exploitation mechanism relies on manipulating path strings to reference resources within legacy extensions that are normally restricted from web page access. This occurs because the extension system fails to properly validate resource paths when processing requests from web content, allowing attackers to construct malicious paths that bypass normal access controls. The vulnerability demonstrates a classic improper access control issue where the security boundaries between extension resources and web content have been weakened or eliminated. This flaw operates at the intersection of resource management and access control, where the system fails to properly enforce resource isolation between different security contexts.
The operational impact of this vulnerability is substantial as it enables malicious websites to potentially access sensitive extension data, configuration information, or functionality that should remain protected from web page access. Attackers could leverage this to extract extension-specific information, manipulate extension behavior, or even gain unauthorized access to extension APIs. The vulnerability affects the fundamental security model of Firefox's extension system and could potentially lead to more severe consequences depending on the capabilities of the affected extensions. This represents a significant threat to user privacy and system security, particularly when users have legacy extensions installed that have not been updated to the newer WebExtensions framework.
Mitigation strategies should focus on upgrading to Firefox 59 or later versions where this vulnerability has been addressed through improved resource access controls and stricter validation of extension resource paths. Users should also disable or remove legacy extensions that are no longer actively maintained and migrate to WebExtensions where possible. Organizations should implement browser security policies that enforce timely updates and monitor for vulnerable browser versions in their environments. This vulnerability aligns with CWE-284 which addresses improper access control, and represents a technique that could be categorized under ATT&CK tactic TA0001 (Initial Access) and technique T1059 (Command and Scripting Interpreter) when exploited by attackers. The fix implemented by Mozilla involved strengthening the validation mechanisms for resource paths and ensuring that legacy extension resources maintain their intended isolation from web content.