CVE-2016-5284 in Firefox
Summary
by MITRE
Mozilla Firefox before 49.0 and Firefox ESR 45.x before 45.4 rely on unintended expiration dates for Preloaded Public Key Pinning, which allows man-in-the-middle attackers to spoof add-on updates by leveraging possession of an X.509 server certificate for addons.mozilla.org signed by an arbitrary built-in Certification Authority.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability described in CVE-2016-5284 represents a critical flaw in Mozilla Firefox's implementation of HTTP Public Key Pinning (HPKP) mechanism, specifically affecting versions prior to 49.0 and Firefox ESR 45.x versions before 45.4. This issue stems from the improper handling of preloaded HPKP policies for the addons.mozilla.org domain, which serves as the primary distribution channel for Firefox add-ons. The vulnerability exploits a fundamental weakness in how Firefox manages certificate validation for add-on updates, creating a pathway for sophisticated man-in-the-middle attacks that can compromise the integrity of the browser extension ecosystem.
The technical flaw manifests through an unintended expiration date mechanism within Firefox's preloaded HPKP configuration for the addons.mozilla.org domain. This misconfiguration allows attackers who possess a valid X.509 server certificate issued by any built-in Certification Authority to successfully impersonate the legitimate add-on update server. The vulnerability specifically targets the HPKP enforcement process, where Firefox relies on preloaded pinning information to verify certificate authenticity. When the expiration date handling becomes flawed, it creates a window where attackers can leverage their certificate possession to bypass normal security checks that should prevent unauthorized certificate usage for the critical add-on update infrastructure.
The operational impact of this vulnerability extends beyond simple certificate validation failures, creating a significant risk to Firefox users' security and privacy. Attackers can exploit this weakness to deliver malicious add-ons that appear legitimate, potentially leading to full system compromise through malicious browser extensions. The attack vector specifically targets the update mechanism for Firefox add-ons, which are trusted components that can execute with elevated privileges within the browser environment. This vulnerability effectively undermines the security model that Firefox employs to protect users from malicious add-on distribution, potentially allowing attackers to establish persistent backdoors or execute arbitrary code through compromised add-on installations.
Mitigation strategies for CVE-2016-5284 require immediate version updates to Firefox 49.0 or Firefox ESR 45.4 and later, which address the flawed expiration date handling in the preloaded HPKP configuration. Organizations should also implement additional network monitoring to detect potential HPKP bypass attempts and ensure that certificate pinning policies are properly enforced. The vulnerability aligns with CWE-295, which covers improper certificate validation, and relates to ATT&CK technique T1195 which addresses phishing attacks through malicious add-ons. Security teams should also consider implementing network-level protections such as DNS filtering and certificate transparency monitoring to detect potential exploitation attempts. Regular security audits of certificate pinning implementations and proactive patch management remain essential defensive measures against similar vulnerabilities in the browser security ecosystem.