CVE-2016-9064 in Firefox
Summary
by MITRE
Add-on updates failed to verify that the add-on ID inside the signed package matched the ID of the add-on being updated. An attacker who could perform a man-in-the-middle attack on the user's connection to the update server and defeat the certificate pinning protection could provide a malicious signed add-on instead of a valid update. This vulnerability affects Firefox ESR < 45.5 and Firefox < 50.
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Analysis
by VulDB Data Team • 11/25/2025
The vulnerability described in CVE-2016-9064 represents a critical flaw in Firefox's add-on update verification mechanism that undermines the security of the browser's extension ecosystem. This weakness specifically affects Firefox Extended Support Release versions prior to 45.5 and standard Firefox versions prior to 50, creating a significant attack surface for malicious actors who can intercept network traffic. The vulnerability stems from insufficient validation of add-on identifiers during the update process, allowing attackers to substitute malicious code for legitimate updates without detection.
The technical flaw manifests in the update verification process where Firefox fails to ensure cryptographic integrity between the add-on ID embedded within a signed package and the actual add-on being updated. This represents a failure in the software supply chain security model, where the system should validate that the digital signature corresponds to the intended target. The vulnerability is classified under CWE-297 which addresses improper validation of certificate subject, and specifically relates to certificate pinning bypass techniques that allow attackers to impersonate legitimate update servers. When an attacker successfully executes a man-in-the-middle attack against the user's connection to the Firefox update server, they can replace a legitimate add-on update with a malicious one that carries a valid signature but targets a different add-on ID.
The operational impact of this vulnerability extends beyond simple code injection, as it enables persistent malicious activity within the user's browser environment. Attackers can leverage this weakness to deliver malware that operates within the browser context, potentially compromising user data, monitoring web traffic, or establishing persistence through browser-based attack vectors. The attack requires the adversary to not only intercept network traffic but also overcome certificate pinning protections, which represents a sophisticated attack scenario that still poses significant risk due to the prevalence of network interception techniques. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under the T1190 category for exploitation of remote services, and specifically targets the T1176 technique for browser extensions and add-ons.
Mitigation strategies for this vulnerability require immediate patching of affected Firefox versions to ensure proper add-on ID verification during update processes. Organizations should implement network monitoring solutions to detect unusual update traffic patterns and consider deploying additional security layers such as proxy servers with SSL inspection capabilities. The fix involves strengthening the verification logic to ensure cryptographic signatures match the intended target add-on identifiers, implementing proper certificate pinning validation, and establishing robust add-on update integrity checks. Security teams should also conduct regular vulnerability assessments of browser extensions and ensure that users maintain updated browser versions to prevent exploitation of this and similar supply chain vulnerabilities.