CVE-2015-0807 in Firefox
Summary
by MITRE
The navigator.sendBeacon implementation in Mozilla Firefox before 37.0, Firefox ESR 31.x before 31.6, and Thunderbird before 31.6 processes HTTP 30x status codes for redirects after a preflight request has occurred, which allows remote attackers to bypass intended CORS access-control checks and conduct cross-site request forgery (CSRF) attacks via a crafted web site, a similar issue to CVE-2014-8638.
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Analysis
by VulDB Data Team • 04/24/2025
The vulnerability described in CVE-2015-0807 represents a critical flaw in the cross-origin resource sharing (CORS) implementation within Mozilla Firefox and Thunderbird browsers. This security issue specifically affects the navigator.sendBeacon API functionality, which is designed to allow web applications to send analytics data and other information to web servers in a reliable manner. The flaw arises from improper handling of HTTP redirect responses during the beacon sending process, creating a pathway for malicious actors to circumvent security restrictions that are normally enforced by CORS policies.
The technical implementation of this vulnerability stems from the browser's processing of HTTP 30x status codes in the context of preflight requests that occur when sending beacons across origins. When a web application attempts to send a beacon to a different origin, the browser typically performs a preflight request to verify that the cross-origin request is permitted according to CORS policies. However, in the affected versions of Firefox and Thunderbird, the implementation incorrectly processes redirect responses that occur after the preflight has been completed, allowing the redirect to proceed without revalidating the CORS permissions that should have been established during the initial preflight phase.
This flaw enables attackers to construct malicious websites that can manipulate the browser's beacon functionality to send requests to protected resources on behalf of authenticated users. The vulnerability essentially allows for cross-site request forgery attacks where the attacker can leverage the legitimate user's browser session to perform unauthorized actions on target servers. The issue is particularly concerning because it operates at the browser level, bypassing traditional web application security controls and potentially allowing attackers to harvest sensitive data or perform actions without the user's knowledge or consent.
The impact of this vulnerability extends beyond simple data theft, as it can enable sophisticated attack patterns that exploit the trust relationship between browsers and web applications. Attackers can craft malicious web pages that send beacons to target servers using the victim's authenticated session, potentially leading to account takeovers, data exfiltration, or other malicious activities. The vulnerability's similarity to CVE-2014-8638 indicates a recurring pattern in browser implementations where CORS validation is not consistently applied across all phases of the request lifecycle, highlighting the complexity of securing cross-origin communications in modern web browsers.
From a security standards perspective, this vulnerability aligns with CWE-346, which addresses "Origin Validation Error" and represents a failure to properly validate the origin of requests. The attack vector follows patterns associated with the ATT&CK technique T1566.001, which involves credential access through the exploitation of web application vulnerabilities. Organizations should consider this vulnerability in their risk assessments as it represents a fundamental breakdown in the browser's security model that could enable attackers to bypass security controls that are typically enforced at the application layer.
Mitigation strategies for this vulnerability require immediate updates to affected browser versions, as the flaw exists in the core browser functionality rather than in web applications. System administrators should prioritize deployment of Firefox 37.0, Firefox ESR 31.6, and Thunderbird 31.6 releases that contain the necessary patches. Additionally, organizations should implement network-level monitoring to detect unusual beacon traffic patterns that might indicate exploitation attempts, while also reviewing their web application security controls to ensure they maintain defense-in-depth measures against potential CSRF attacks. The vulnerability underscores the importance of keeping browser software updated and demonstrates how low-level implementation flaws can create significant security risks that affect entire user populations rather than isolated applications.