CVE-2017-5389 in Firefox
Summary
by MITRE
WebExtensions could use the "mozAddonManager" API by modifying the CSP headers on sites with the appropriate permissions and then using host requests to redirect script loads to a malicious site. This allows a malicious extension to then install additional extensions without explicit user permission. This vulnerability affects Firefox < 51.
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Analysis
by VulDB Data Team • 11/04/2022
The vulnerability identified as CVE-2017-5389 represents a critical security flaw in Mozilla Firefox's WebExtensions architecture that undermines the browser's permission model and extension security boundaries. This weakness specifically targets the mozAddonManager API, which is designed to provide extensions with controlled access to addon management functions while maintaining user consent and security boundaries. The vulnerability stems from improper Content Security Policy (CSP) header handling that allows malicious extensions to bypass normal security restrictions. When an extension with appropriate permissions modifies CSP headers on targeted websites, it can manipulate the browser's security context to redirect script loading operations to attacker-controlled domains. This manipulation effectively creates a pathway for malicious extensions to execute arbitrary code in the context of the user's browsing session, leveraging the legitimate extension permissions to gain elevated privileges.
The technical exploitation of this vulnerability occurs through a sophisticated multi-stage attack vector that combines CSP header manipulation with host request redirection capabilities. Attackers can craft malicious extensions that, when installed, modify CSP policies on legitimate websites to permit script loading from attacker-controlled domains. This technique exploits the browser's trust model where certain extensions are granted permissions to interact with web content, but the security boundaries are not properly enforced during the redirection process. The vulnerability specifically affects Firefox versions prior to 51, indicating that the underlying flaw existed in the browser's WebExtensions implementation where the CSP enforcement mechanism was insufficient to prevent malicious redirection patterns. The attack chain begins with an extension that has been granted appropriate permissions, typically through user installation, then leverages the extension's ability to modify page content and headers to establish a malicious redirect that ultimately allows the installation of additional unwanted extensions without explicit user consent.
The operational impact of CVE-2017-5389 extends beyond simple unauthorized extension installation, representing a fundamental breach in Firefox's extension security architecture that could enable full compromise of user browsing sessions. This vulnerability allows attackers to silently install additional malicious extensions that can persist across browser sessions and potentially access sensitive user data, modify browser behavior, or establish persistent backdoors. The implications are particularly severe because the attack requires only a single malicious extension to be installed, as opposed to multiple separate attacks or complex exploitation chains. The vulnerability effectively undermines the principle of least privilege that governs extension permissions, allowing malicious actors to expand their attack surface through automated extension installation processes. This flaw particularly affects users who may have installed seemingly legitimate extensions that could later be compromised or replaced by malicious actors exploiting this vulnerability, creating a persistent threat vector that operates outside of normal user awareness and security controls.
Mitigation strategies for CVE-2017-5389 focus primarily on upgrading to Firefox version 51 or later, where Mozilla implemented comprehensive fixes to the WebExtensions API security model. The remediation addresses the core issue by strengthening CSP header enforcement mechanisms and implementing stricter validation of extension permissions during script loading operations. Organizations should also implement strict extension management policies that limit the installation of third-party extensions and regularly audit installed extensions for suspicious behavior. Browser security configurations should be reviewed to ensure that CSP policies are properly enforced and that extensions with elevated permissions are carefully monitored. Additionally, users should be educated about the risks of installing extensions from untrusted sources and the importance of keeping browser software updated. This vulnerability aligns with CWE-284, which addresses improper access control in software systems, and maps to ATT&CK technique T1106 for execution through legitimate user processes. The fix implemented by Mozilla involved strengthening the extension permission model to prevent unauthorized access to the mozAddonManager API through manipulated CSP headers, effectively closing the attack vector that allowed malicious extensions to install additional software without explicit user consent.