CVE-2026-74953 in Firefox
Summary
by MITRE • 08/18/2026
Privilege escalation in the Networking: Cookies component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, 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 within Mozilla Firefox's networking subsystem, specifically affecting the cookie management component. This vulnerability allows an attacker to manipulate browser state in a manner that bypasses intended access controls, potentially granting unauthorized privileges or data exposure capabilities beyond what is permitted by standard web application policies. The core of this defect lies in how the browser handles session identifiers and persistent storage mechanisms during network operations, where improper validation or logic errors enable malicious actors to elevate their scope from untrusted script execution to accessing sensitive user credentials or modifying security-sensitive attributes that should remain immutable under normal browsing conditions.
From a technical perspective, cookie handling is fundamental to maintaining state across HTTP requests, yet it also presents a significant attack surface when not rigorously enforced against cross-origin and same-site restrictions. In this specific instance, the flaw likely stems from an inconsistency in how Firefox processes Set-Cookie headers or updates existing cookies based on origin attributes such as SameSite, Secure, and HttpOnly flags. An attacker could exploit this by crafting malicious web content that triggers unintended cookie modifications, effectively hijacking session tokens or injecting administrative-level identifiers into a user's context without proper authentication checks. This type of vulnerability is particularly dangerous because it undermines the isolation guarantees provided by the browser sandboxing mechanisms, allowing code running in one origin to interfere with security policies governing another.
The operational impact of this privilege escalation vector is severe for end-users and enterprise environments alike. Successful exploitation could lead to session hijacking, where an attacker takes over a user's active login state, gaining full access to their accounts on targeted websites. Furthermore, if the elevated privileges allow modification of cookies that control application behavior or administrative settings within web-based management interfaces, it could result in complete compromise of those services. For organizations relying on Firefox for secure browsing, this vulnerability poses a risk of data exfiltration and unauthorized actions performed under the guise of legitimate users, potentially leading to significant financial loss, reputational damage, and regulatory non-compliance depending on the sensitivity of the accessed data.
This type of flaw is commonly categorized under CWE-269 Improper Privilege Management or CWE-748 Incorrect Default Permissions within the Common Weakness Enumeration framework, as it involves a failure to properly restrict access rights for specific components or contexts. In terms of tactical classification according to MITRE ATT&CK, this vulnerability aligns with techniques related to Credential Access and Defense Evasion, specifically those involving browser-based attacks such as cookie theft or manipulation (T1539) and potentially bypassing security restrictions through client-side logic exploitation (T1068). These classifications highlight the need for robust input validation and strict enforcement of origin boundaries in all network-related operations.
To mitigate this risk, users must immediately update their Firefox installations to version 154 or later, including Firefox ESR versions 140.14 and 153.1, where these specific code paths have been patched. Security administrators should ensure that automatic updates are enabled for all endpoints within the organization to prevent exposure during any window of vulnerability exploitation. Additionally, implementing strict Content Security Policies (CSP) can help mitigate some downstream effects by restricting how scripts interact with cookies and other storage mechanisms. Regular security audits focusing on browser configuration and extension permissions further reduce the attack surface associated with such client-side vulnerabilities.