CVE-2026-74955 in Firefox
Summary
by MITRE • 08/18/2026
Privilege escalation in the Request Handling component. This vulnerability was fixed in Firefox 154 and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/18/2026
The identified security issue represents a critical privilege escalation flaw located within the request handling subsystem of Mozilla Firefox, specifically affecting versions prior to release 154 and Extended Support Release version 153.1. This vulnerability stems from an improper validation or enforcement mechanism during the processing of network requests, allowing a lower-privileged context, such as content running in a web page sandbox, to execute actions that should be restricted to higher-privilege contexts like chrome code or system-level processes. In modern browser architectures, strict isolation between untrusted web content and trusted browser internals is paramount for maintaining user security. When this boundary is compromised through flawed request handling logic, an attacker can bypass intended access controls, effectively gaining elevated permissions within the application environment.
From a technical perspective, such privilege escalation vulnerabilities often arise when internal APIs or interfaces are exposed to external scripts without adequate checks on the origin of the caller or the nature of the data being processed. The flaw likely involves a scenario where maliciously crafted network requests trigger code paths that assume higher trust levels than warranted by their source. This could involve manipulating headers, URLs, or request parameters in ways that confuse the internal state machine of the browser's networking stack. By exploiting this logic error, an adversary can potentially access sensitive user data, modify application settings, or execute arbitrary commands with the privileges of the running Firefox process. The impact is severe because it undermines the fundamental security model of the web platform, which relies on sandboxing to prevent malicious websites from affecting the host system or other tabs.
The operational impact of this vulnerability extends beyond simple data theft. An attacker who successfully exploits this flaw could establish a persistent foothold within the user's browsing session, potentially leading to further lateral movement if the browser is integrated with enterprise environments or sensitive applications. It also poses significant risks for users accessing banking portals, email services, or corporate intranets, as the compromised context might have access to cookies, local storage, and other authentication tokens that are typically protected from cross-site scripting attacks. The ability to escalate privileges effectively neutralizes many of the protective measures browsers employ against web-based attacks, making this a high-severity issue requiring immediate attention.
To mitigate the risks associated with this vulnerability, users must upgrade their Firefox installation immediately to version 154 or later, including the Extended Support Release branch updated to version 153.1. These releases contain the necessary patches that correct the request handling logic and enforce stricter boundaries between different privilege levels within the browser engine. For organizations deploying Firefox across multiple endpoints, it is advisable to verify deployment configurations ensure automatic updates are enabled so that all users receive these critical security fixes without delay. Additionally, while waiting for patch application, administrators should consider implementing network-level controls or content security policies where feasible to restrict potentially malicious request patterns, although software update remains the primary and most effective remediation strategy.
This vulnerability aligns with common weakness enumerations related to improper privilege management and access control failures. Specifically, it reflects issues categorized under CWE-269 Improper Privilege Management or CWE-732 Incorrect Permission Assignment for Critical Resource, depending on whether the flaw lies in assigning roles incorrectly or failing to restrict resource access based on those roles. In terms of adversary tactics, this type of exploitation is consistent with techniques found in the MITRE ATT&CK framework under privilege escalation vectors, where attackers seek to increase their level of access within a compromised system to achieve broader objectives such as data exfiltration or persistence. Understanding these classifications helps security teams prioritize remediation efforts and align defensive strategies with industry-standard threat models.