CVE-2026-118003 in Firefox
Summary
by MITRE • 10/27/2026
Information disclosure in the Networking: DNS component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified security issue resides within the Domain Name System (DNS) resolution subsystem of Mozilla Firefox, specifically affecting versions prior to 159 for standard releases and before version 153.6 for Extended Support Release channels. This vulnerability is classified as an information disclosure flaw, which typically involves the unintended exposure of sensitive data that could aid an attacker in further exploitation or reconnaissance activities against a user's system or network infrastructure. In the context of web browsers, DNS-related vulnerabilities often stem from how query responses are processed, cached, or logged internally before being passed to the application layer for rendering content.
From a technical perspective, such flaws may arise due to improper sanitization of DNS response data, excessive logging of resolution queries that might contain sensitive domain names associated with private networks or internal services, or memory handling errors during the parsing of complex DNS records like CNAME chains or TXT records containing encoded payloads. When an attacker controls or influences a malicious website they wish to target, they may craft specific DNS responses designed to trigger this disclosure mechanism. The browser's networking stack might inadvertently expose details about the local network topology, internal IP addresses, or other metadata that should remain opaque to external web content through cross-origin requests or side-channel observations derived from timing differences in resolution processes.
The operational impact of this vulnerability centers on privacy degradation and potential facilitation of more severe attacks such as Local Network Scanning or Service Discovery. By exploiting the information leak, an adversary could map out internal network structures that are not directly accessible via standard HTTP/HTTPS protocols but can be inferred through DNS behavior. This aligns with MITRE ATT&CK techniques related to Resource Development and Collection, particularly those involving passive reconnaissance where attackers gather intelligence without direct interaction with target systems beyond initial web page loading. For enterprise environments relying on Firefox ESR for stability, this represents a significant risk as internal services often rely on the assumption that browser-based DNS queries do not leak sensitive architectural details to external parties.
Mitigation strategies primarily involve immediate patching of all affected browsers to versions 159 and above for standard users or 153.6 and above for enterprise deployments, ensuring that the underlying fixes in the networking component are applied. These updates typically include stricter validation rules for DNS responses, reduced verbosity in internal logging mechanisms regarding resolution paths, and enhanced isolation between network stack operations and web content execution contexts to prevent data leakage across security boundaries. Organizations should also enforce automatic update policies where feasible to minimize exposure windows and consider deploying browser hardening configurations that restrict unnecessary DNS query behaviors if the environment allows for such policy enforcement through group management tools.