CVE-2026-109767 in Firefox
Summary
by MITRE • 10/13/2026
Information disclosure in the Networking component. This vulnerability was fixed in Firefox 158 and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/13/2026
The identified vulnerability resides within the networking subsystem of Mozilla Firefox, specifically affecting versions prior to 158 for standard releases and version 153.5 for Extended Support Release channels. This flaw is categorized as an information disclosure issue, which typically involves the unintended exposure of sensitive data that should remain confidential or restricted in scope. In the context of web browsers, networking components are responsible for handling HTTP requests, managing cookies, processing cache entries, and facilitating communication between client-side scripts and remote servers. A vulnerability in this layer can lead to scenarios where internal state information, network topology details, authentication tokens, or private user data is exposed to unauthorized parties through side channels, error messages, or improper memory management practices.
From a technical perspective, such vulnerabilities often stem from insufficient validation of input parameters passed to networking functions, race conditions during asynchronous request handling, or the leakage of internal buffer contents due to out-of-bounds reads. Attackers may exploit these weaknesses by crafting malicious web pages that trigger specific network operations designed to leak memory addresses, DNS query results, or cached credentials. The exploitation vector usually involves social engineering tactics where a victim is induced to visit a specially crafted website or interact with embedded content from untrusted sources. Once triggered, the vulnerability allows an attacker to gather intelligence about the target environment, which can serve as a precursor for more severe attacks such as session hijacking, cross-site request forgery, or targeted phishing campaigns based on revealed user behavior and data preferences.
The operational impact of this information disclosure is significant because it undermines the fundamental security model of web browsing, which relies heavily on isolation between different origins and sites. By leaking internal network state or private data, the vulnerability erodes trust in the browser's ability to protect user privacy. This can lead to direct financial loss if sensitive credentials are exposed, reputational damage for organizations using Firefox as their primary enterprise browser, and increased risk of identity theft for individual users. Furthermore, the availability of such detailed internal information facilitates further reconnaissance by attackers, allowing them to tailor subsequent exploits with greater precision against specific systems or user profiles identified through the leaked data.
To mitigate this vulnerability, it is imperative that all affected instances of Firefox are updated immediately to version 158 for standard releases and version 153.5 for ESR channels. These updates contain patches developed by Mozilla's security team to address the underlying flaws in the networking component. Organizations should enforce automated update policies to ensure rapid deployment across all endpoints. Additionally, users can enhance their defense posture by employing content blocking extensions that restrict third-party cookies and tracking scripts, thereby reducing the attack surface available for exploitation. Regular monitoring of browser version compliance within enterprise environments is also recommended to prevent exposure to known vulnerabilities until patches are applied.
This incident aligns with Common Weakness Enumeration (CWE) categories such as CWE-200: Exposure of Sensitive Information to an Unauthorized Actor and potentially CWE-125: Out-of-bounds Read, depending on the specific implementation details confirmed by Mozilla in their security advisory. In terms of tactical mapping within the MITRE ATT&CK framework, this vulnerability supports techniques related to Collection from Browser or Credential Access via Browser Dumping if sensitive data is exfiltrated, as well as Discovery activities where attackers gather information about the victim's environment. Continuous vigilance and adherence to recommended patch management cycles are essential for maintaining a robust security posture against such network-level exploits.