CVE-2018-5135 in Firefox
Summary
by MITRE
WebExtensions can bypass normal restrictions in some circumstances and use "browser.tabs.executeScript" to inject scripts into contexts where this should not be allowed, such as pages from other WebExtensions or unprivileged "about:" pages. This vulnerability affects Firefox < 59.
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Analysis
by VulDB Data Team • 02/05/2021
The vulnerability identified as CVE-2018-5135 represents a critical security flaw in the Firefox browser's WebExtensions architecture that undermines the fundamental security boundaries designed to protect users from malicious extensions. This issue specifically targets the privilege escalation mechanisms within Firefox's extension framework, where WebExtensions can potentially circumvent normal access controls and execute unauthorized script injections. The vulnerability exists in Firefox versions prior to 59, making it a significant concern for users running older browser versions that remain exposed to potential exploitation.
The technical flaw resides in the improper enforcement of security restrictions within Firefox's WebExtensions API implementation, particularly concerning the browser.tabs.executeScript function. This function is designed to execute JavaScript code within specific browser contexts, but the vulnerability allows extensions to bypass normal restrictions and inject scripts into contexts where such execution should be prohibited. The affected contexts include pages belonging to other WebExtensions and unprivileged "about:" pages, which are typically protected from arbitrary script injection to maintain browser security and user privacy. This bypass mechanism essentially creates a pathway for malicious extensions to access and manipulate data in contexts where they should not have access, fundamentally compromising the extension sandboxing model.
The operational impact of this vulnerability is severe and multifaceted, as it enables attackers to perform privilege escalation attacks that could lead to complete browser compromise. When a malicious WebExtension exploits this vulnerability, it can inject scripts into other extensions' contexts, potentially allowing for data theft, credential harvesting, or manipulation of browser functionality. The ability to execute code in unprivileged "about:" pages particularly concerning since these pages often contain sensitive system information or administrative controls. Attackers could leverage this vulnerability to gain unauthorized access to browser internals, monitor user activities across different extensions, or even modify the behavior of legitimate extensions. This vulnerability directly violates the principle of least privilege that is fundamental to browser security architectures.
This vulnerability aligns with CWE-284, which addresses improper access control mechanisms, and represents a clear violation of the security model that separates different extension contexts. The flaw also maps to ATT&CK technique T1176, which involves the use of web browsers as a vector for privilege escalation and persistence. The vulnerability demonstrates how insufficient input validation and access control enforcement in browser extension APIs can create persistent security risks. Organizations and users should prioritize immediate remediation by upgrading to Firefox version 59 or later, which includes patches addressing this specific bypass mechanism. Additionally, administrators should implement strict extension management policies, regularly audit installed extensions, and consider implementing browser hardening measures to reduce the attack surface. The vulnerability underscores the critical importance of maintaining up-to-date browser software and the necessity of robust security controls in extension ecosystems, as these components form the primary defense against user-facing browser-based attacks.