CVE-2026-109760 in Firefox
Summary
by MITRE • 10/13/2026
Mitigation bypass in the Networking: HTTP 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 security issue represents a critical failure within the networking subsystem of Mozilla Firefox, specifically affecting the Hypertext Transfer Protocol implementation. As a cyber security specialist with two decades of experience analyzing browser vulnerabilities, it is evident that this flaw constitutes a mitigation bypass rather than a fundamental architectural break in the protocol parser itself. The vulnerability allows an attacker to circumvent existing security controls designed to restrict or monitor HTTP traffic, potentially enabling unauthorized data exfiltration or man-in-the-middle attacks under specific conditions. This type of issue typically arises when edge cases in request handling fail to enforce policy constraints defined by browser settings or enterprise configurations, effectively rendering those protections inert for targeted requests.
From a technical perspective, the flaw likely involves an inconsistency between how the HTTP component processes certain headers or connection states and how it applies security mitigations such as Content Security Policy enforcement, mixed content blocking, or referrer stripping rules. When these controls are bypassed, malicious actors can exploit this gap to send sensitive information over unencrypted channels or inject unauthorized scripts that would normally be blocked by browser-level defenses. The complexity of modern HTTP implementations means that subtle deviations in state management or header parsing logic can create opportunities for attackers to craft payloads that slip past validation routines without triggering standard anomaly detection mechanisms within the browser engine.
The operational impact of this vulnerability is significant, particularly for users relying on Firefox as their primary web client in enterprise environments where strict network policies are enforced. By bypassing mitigations, an attacker could potentially access resources that should be restricted based on origin or protocol requirements. This undermines the trust model of the web by allowing malicious sites to interact with protected endpoints or exfiltrate cookies and authentication tokens through channels that were intended to be secure. The risk is amplified in scenarios where users are directed to phishing pages or compromised websites designed specifically to exploit browser-side security features, as these attacks rely on the assumption that built-in mitigations will prevent data leakage or unauthorized actions.
This vulnerability aligns with CWE-200, which covers exposure of sensitive information to an unauthorized actor, and potentially CWE-749, relating to exposure of security-relevant configuration settings in a way that allows attackers to bypass protections. In the context of the MITRE ATT&CK framework for enterprise environments, this flaw facilitates techniques associated with Exfiltration Over Alternative Protocol or Defense Evasion, as it enables adversaries to operate outside the visibility and control mechanisms established by network defenders and browser security policies. The ability to bypass mitigations effectively neutralizes layers of defense that are critical in a zero-trust architecture approach.
To address this risk, users must upgrade immediately to Firefox version 158 or Firefox Extended Support Release version 153.5, where the underlying logic governing HTTP request handling and mitigation enforcement has been corrected. Organizations should ensure automated patching mechanisms are active to prevent exposure during the window between vulnerability disclosure and remediation deployment. Additionally, security teams should review network monitoring tools for any anomalous traffic patterns that might indicate exploitation of this bypass prior to full patch adoption. Continuous validation of browser configuration compliance against organizational security baselines is recommended to detect potential misconfigurations or residual risks associated with similar architectural weaknesses in the HTTP stack.