CVE-2026-118000 in Firefox
Summary
by MITRE • 10/27/2026
Information disclosure in the Networking: HTTP component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/27/2026
The identified security issue resides within the networking subsystem of Mozilla Firefox, specifically affecting its Hypertext Transfer Protocol implementation. As a critical component responsible for managing all web traffic, this module handles the construction, transmission, and parsing of HTTP requests and responses between the browser client and remote servers. The vulnerability constitutes an information disclosure flaw, which implies that under specific conditions or through particular sequences of operations, sensitive data intended to remain internal to the application's processing logic may be inadvertently exposed to external entities or other parts of the system with lower privilege levels. This type of defect is particularly concerning in web browsers because they operate at the intersection of user privacy and network security, making any leakage potentially exploitable for further attacks such as session hijacking, credential theft, or targeted reconnaissance against the victim's browsing habits and internal network topology.
From a technical perspective, information disclosure vulnerabilities often stem from improper handling of error states, excessive logging, or incorrect memory management within protocol parsers. In the context of HTTP processing, this could involve leaking headers that contain authentication tokens, exposing stack traces during parsing errors, or revealing details about cached content that should be ephemeral. The flaw likely arises when the browser fails to sanitize output data before it is sent over the network or stored in accessible memory regions. Such oversights allow an attacker who can influence the HTTP request flow, perhaps through a malicious website or a compromised extension, to trigger conditions where internal state information becomes visible. This visibility provides adversaries with valuable intelligence that can be leveraged to refine subsequent attacks, bypass security controls, or exploit related weaknesses in dependent services.
The operational impact of this vulnerability is significant due to the widespread adoption of Firefox and its enterprise variants like Extended Support Release versions used by many organizations for their stability and long-term support cycles. For individual users, exposure could lead to privacy violations where browsing history, cookies, or session identifiers are leaked, potentially leading to account compromise if combined with other attack vectors. For corporate environments relying on Firefox ESR 153.6, the risk extends to potential leakage of internal network information or sensitive business data transmitted over HTTP connections that were assumed to be secure from browser-side leaks. The existence of such a flaw undermines trust in the browser's ability to isolate web content and protect user identity, which are foundational principles of modern web security architectures.
This vulnerability aligns with Common Weakness Enumeration category CWE-200, which covers Exposure of Sensitive Information to an Unauthorized Actor. It also relates to ATT&CK technique T1537, Transfer Data to Cloud Account, if the disclosure facilitates data exfiltration, or more broadly fits within initial access and discovery phases where attackers gather information about a target's environment. The remediation strategy employed by Mozilla involves patching the underlying HTTP component code in Firefox 159 and Firefox ESR 153.6. Users are strongly advised to update their browsers immediately to mitigate this risk. Organizations should enforce automated update policies for all endpoints running affected versions, particularly those using ESR releases which may lag behind standard release cycles due to testing requirements. Additionally, implementing strict Content Security Policies and monitoring network traffic for anomalous data patterns can provide an additional layer of defense against exploitation attempts while updates are being deployed across the infrastructure.