CVE-2026-96869 in Firefox
Summary
by MITRE • 09/29/2026
Information disclosure in the Networking component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, and Firefox ESR 140.17.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 09/29/2026
The identified security issue resides within the networking subsystem of Mozilla Firefox, representing a classic information disclosure vulnerability that allows unauthorized access to sensitive internal state or data structures. In web browser architectures, the networking component is responsible for managing all communication between the user agent and remote servers, handling tasks such as DNS resolution, TCP connection establishment, TLS negotiation, and HTTP request routing. When this subsystem contains flaws related to memory management or logic errors in how it exposes internal variables to JavaScript contexts or other processes, it can lead to unintended leakage of information that should remain isolated from untrusted code. This type of vulnerability is particularly dangerous because the networking layer operates at a privileged level relative to web content, meaning any breach here effectively bypasses many standard sandboxing protections designed to isolate malicious scripts from the underlying operating system and browser internals.
From a technical perspective, this flaw likely involves improper handling of memory buffers or state variables within the network stack, potentially allowing an attacker who controls a webpage to read sensitive data such as authentication tokens, session identifiers, internal IP addresses, or other contextual information that is not intended for public exposure. Such leaks can occur through side-channel attacks where timing differences reveal secret values, or more directly through APIs that fail to properly sanitize output before returning it to the calling context. The presence of this vulnerability indicates a gap in the boundary checks between privileged browser components and untrusted web content, which contradicts the principle of least privilege essential for secure software design. Attackers could exploit this by crafting malicious pages that trigger specific network operations designed to expose these hidden states, thereby gaining insights into the user's browsing habits or compromising active sessions without requiring additional privileges like keylogging or screen capture.
The operational impact of such an information disclosure vulnerability is significant, as it can serve as a stepping stone for more severe attacks including session hijacking and cross-site request forgery. If sensitive cookies or authentication headers are leaked through this flaw, attackers can impersonate the user on targeted services, leading to unauthorized access to personal accounts, financial data, or corporate resources. Furthermore, knowledge of internal network topology or IP addresses gained through such leaks can facilitate more sophisticated lateral movement in enterprise environments where Firefox is deployed as a standard browser. The vulnerability undermines trust in the browser's ability to maintain confidentiality and integrity, potentially eroding user confidence in secure browsing practices. It also complicates incident response efforts because traditional logging mechanisms may not capture these subtle data exfiltration events, making detection difficult without specialized monitoring tools focused on network behavior anomalies.
To mitigate this risk, users must immediately update their Firefox installations to version 157 or the Extended Support Release versions 140.17 and 153.4, which contain the necessary patches to address these memory handling deficiencies. Organizations should enforce automated patch management policies to ensure that all endpoints are updated promptly upon release of security fixes. Additionally, implementing strict Content Security Policy headers can help limit the impact by restricting how scripts interact with network resources, although this is a compensatory control rather than a fix for the underlying flaw. Developers and security teams should also review similar networking components in other software to identify potential analogous issues, applying rigorous code reviews focused on memory safety and access control boundaries. Regular penetration testing that includes scenarios designed to probe for information leakage through browser APIs can further validate the effectiveness of these mitigations and ensure continued resilience against evolving attack techniques.
This vulnerability aligns with Common Weakness Enumeration category CWE-200, which covers Information Exposure, specifically highlighting failures in restricting data access to authorized entities. It also relates to MITRE ATT&CK technique T1537, Transfer Data to Cloud Account via Custom Protocol, as attackers may leverage such leaks to exfiltrate sensitive information over encrypted channels undetected by standard security controls. Understanding the context of this flaw within the broader landscape of browser vulnerabilities emphasizes the importance of continuous monitoring and rapid response cycles in maintaining a robust defense posture against sophisticated adversaries who constantly seek new vectors for data theft.