CVE-2018-5134 in Firefox
Summary
by MITRE
WebExtensions may use "view-source:" URLs to view local "file:" URL content, as well as content stored in "about:cache", bypassing restrictions that only allow WebExtensions to view specific content. This vulnerability affects Firefox < 59.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 02/17/2020
This vulnerability in Firefox represents a significant bypass of web extension security restrictions that could enable malicious actors to access sensitive local content. The flaw specifically affects Firefox versions prior to 59 where WebExtensions could exploit the "view-source:" protocol handler to circumvent intended access controls. The vulnerability allows extensions to retrieve content from local file system locations and cached data stored in about:cache, which should normally be restricted to prevent unauthorized access to user data. This represents a direct violation of the principle of least privilege that governs how browser extensions should operate within the security boundaries of the browser environment.
The technical implementation of this vulnerability exploits the improper handling of URL schemes within Firefox's WebExtensions framework. When a WebExtension attempts to access content using the "view-source:" prefix, the browser should enforce strict access controls to prevent unauthorized viewing of local files or cached content. However, this flaw allows the extension to bypass these controls by leveraging the special handling of "file:" and "about:" URLs within the view-source context. The vulnerability specifically targets the security model that separates extension permissions from direct system access, creating a path for extensions to indirectly access content that should remain protected from extension-level access. This type of flaw falls under the category of privilege escalation through protocol handler manipulation.
The operational impact of this vulnerability extends beyond simple information disclosure, as it could enable attackers to harvest sensitive user data from local storage, cached web pages, and system files that extensions should never be able to access directly. An attacker could craft a malicious WebExtension that, when installed, would be able to view cached web content including login credentials, personal information, or other sensitive data stored in Firefox's cache. The vulnerability affects the fundamental security model of Firefox's extension architecture, potentially allowing for data exfiltration, credential theft, or other malicious activities that exploit the trust relationship between the browser and extensions. This flaw directly impacts user privacy and system security by undermining the sandboxing mechanisms designed to protect users from potentially malicious extensions.
Mitigation strategies for this vulnerability require immediate patching of affected Firefox versions to 59 or later where the issue has been resolved through proper enforcement of access controls. Organizations should implement strict extension management policies that limit the installation of third-party extensions and regularly audit installed extensions for suspicious behavior. Users should be educated about the risks of installing extensions from untrusted sources and the importance of keeping browsers updated. The fix implemented by Mozilla addresses the root cause by properly validating URL access within the view-source protocol handler and enforcing stricter access controls on file and cache content. This vulnerability demonstrates the importance of thorough security testing of protocol handlers and access control mechanisms, aligning with security best practices outlined in the OWASP Top Ten and NIST cybersecurity frameworks that emphasize proper input validation and access control enforcement. The issue also highlights the need for continuous monitoring of browser security updates and the implementation of automated patch management systems to prevent exploitation of known vulnerabilities.