CVE-2026-120627 in Extension
Summary
by MITRE • 11/02/2026
The Private Internet Access Extension for Firefox contains an unguarded onAuthRequired authentication handler, leading to leakage of PIA proxy credentials when a user visits any malicious website that issues a Basic auth challenge. This issue was fixed in version 3.2.5, but reintroduced in later versions.
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Analysis
by VulDB Data Team • 11/02/2026
The vulnerability identified within the Private Internet Access browser extension for Firefox represents a critical authentication handler flaw rooted in improper access control and credential management practices. Specifically, the onAuthRequired event listener is implemented without sufficient safeguards to distinguish between legitimate proxy servers requiring authentication and malicious third-party websites attempting to intercept credentials through standard HTTP Basic Authentication challenges. This architectural oversight allows any website visited by the user that issues an unauthenticated or improperly scoped challenge to trigger the handler, thereby exposing sensitive proxy credentials directly to potentially hostile entities. The core technical flaw lies in the lack of strict origin validation or scope restriction within the authentication callback function, which fails to verify whether the requesting resource is part of the trusted Private Internet Access infrastructure before transmitting stored secrets.
From a security taxonomy perspective, this vulnerability aligns closely with CWE-798: Use of Hard-coded Credentials and CWE-200: Exposure of Sensitive Information to an Unauthorized Actor. The extension essentially treats all authentication challenges equally, regardless of their source domain or intent. When a user navigates to a malicious site designed to mimic a proxy server or simply issues a Basic Auth challenge via JavaScript or HTTP headers, the browser invokes the onAuthRequired handler provided by the extension. Because the handler does not validate that the request originates from a trusted PIA endpoint, it automatically supplies the stored username and password for the private proxy service. This behavior effectively bypasses the intended isolation boundaries of the browser's same-origin policy regarding credential leakage through active authentication prompts.
The operational impact of this vulnerability is severe, as it compromises the confidentiality of user credentials that are typically used to access a secure virtual private network infrastructure. If an attacker successfully captures these credentials via a malicious website, they can impersonate the victim within the Private Internet Access ecosystem. This could lead to unauthorized usage of proxy services, potential billing fraud if associated with paid accounts, or more critically, it may facilitate further attacks such as man-in-the-middle scenarios where the attacker uses the stolen credentials to route traffic through their own controlled infrastructure while appearing legitimate to downstream servers. Furthermore, since browser extensions often have elevated privileges compared to standard web pages, this leakage undermines the trust model of the extension system itself, potentially eroding user confidence in similar privacy-focused tools.
Although a fix was initially deployed in version 3.2.5, the reintroduction of this flaw in subsequent versions indicates a regression in security testing or code review processes. This recurrence highlights the importance of continuous integration and automated security scanning for browser extensions that handle sensitive data. To mitigate such risks, developers must implement strict origin whitelisting within authentication handlers to ensure credentials are only transmitted when the request URL matches known trusted domains associated with the service provider. Additionally, adopting principles from the MITRE ATT&CK framework, specifically techniques related to Credential Access and Browser Extension Abuse, underscores the need for defense-in-depth strategies such as limiting extension permissions to specific origins rather than broad access patterns. Users should remain vigilant by keeping their extensions updated to versions where this regression has been permanently resolved and considering multi-factor authentication if supported by the service provider to reduce reliance on static credentials alone.