CVE-2016-9902 in Firefox
Summary
by MITRE
The Pocket toolbar button, once activated, listens for events fired from it's own pages but does not verify the origin of incoming events. This allows content from other origins to fire events and inject content and commands into the Pocket context. Note: this issue does not affect users with e10s enabled. This vulnerability affects Firefox ESR < 45.6 and Firefox < 50.1.
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Analysis
by VulDB Data Team • 11/25/2025
The vulnerability identified as CVE-2016-9902 represents a critical security flaw in the Pocket toolbar button implementation within Mozilla Firefox browsers. This issue stems from a fundamental lack of origin verification mechanisms within the event handling system of the Pocket extension, creating a significant attack vector that could be exploited by malicious actors to gain unauthorized access to the Pocket context. The vulnerability specifically affects users running Firefox ESR versions prior to 45.6 and standard Firefox versions prior to 50.1, making it a widespread concern for organizations and individuals using these older browser versions.
The technical flaw manifests in the Pocket toolbar button's event processing logic, where the system fails to validate the source of incoming events before executing them. This design oversight creates a cross-origin execution vulnerability that allows content from external domains to impersonate legitimate Pocket events and inject malicious commands or content into the Pocket context. The vulnerability operates at the browser extension level, exploiting the trust relationship between the Pocket toolbar and its own pages without proper origin validation checks. This behavior directly violates security principles of least privilege and input validation, as the system accepts potentially harmful events without confirming their legitimate source.
The operational impact of this vulnerability extends beyond simple content injection, potentially enabling attackers to execute arbitrary commands within the Pocket extension context. An attacker could leverage this flaw to modify user bookmarks, inject malicious scripts, or even redirect users to phishing sites through the Pocket toolbar. The attack surface is particularly concerning because the Pocket toolbar is typically installed and enabled by users who trust the Pocket service, making social engineering attacks more effective. This vulnerability also demonstrates the importance of proper sandboxing and origin validation in browser extensions, as the lack of such mechanisms can compromise the entire browser security model. The issue affects the browser's security architecture by creating an unauthorized execution path that bypasses normal security boundaries.
Mitigation strategies for CVE-2016-9902 primarily focus on updating to patched browser versions where Mozilla has implemented proper origin verification for Pocket toolbar events. Organizations should prioritize immediate deployment of Firefox ESR 45.6 or Firefox 50.1, which include the necessary security fixes. Additionally, administrators should consider implementing browser hardening measures such as disabling unnecessary extensions and ensuring users are educated about the risks of using outdated browser versions. The vulnerability highlights the importance of security standards such as CWE-20, which addresses improper input validation, and aligns with ATT&CK techniques related to privilege escalation and code injection. Organizations should also implement monitoring for unusual Pocket extension activity and consider using security tools that can detect unauthorized extension modifications. The fix implemented by Mozilla addresses the root cause by adding proper origin verification checks to the Pocket toolbar event handling system, ensuring that only events from legitimate Pocket pages can execute commands within the extension context. This vulnerability serves as a reminder of the critical importance of maintaining up-to-date browser software and the potential risks associated with legacy browser versions in enterprise security environments.