CVE-2015-0816 in Firefox
Summary
by MITRE
Mozilla Firefox before 37.0, Firefox ESR 31.x before 31.6, and Thunderbird before 31.6 do not properly restrict resource: URLs, which makes it easier for remote attackers to execute arbitrary JavaScript code with chrome privileges by leveraging the ability to bypass the Same Origin Policy, as demonstrated by the resource: URL associated with PDF.js.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 11/25/2025
The vulnerability identified as CVE-2015-0816 represents a critical security flaw in Mozilla Firefox and Thunderbird browsers that stems from improper handling of resource: URLs within the browser's security model. This weakness allows remote attackers to bypass the fundamental Same Origin Policy that normally protects web applications from cross-site scripting attacks. The issue specifically affects versions prior to Firefox 37.0 and Firefox ESR 31.x before 31.6, as well as Thunderbird versions before 31.6, creating a window of exposure for users running these outdated browser versions. The vulnerability is particularly dangerous because it enables attackers to execute arbitrary JavaScript code with chrome privileges, which are the highest level of privileges available within the browser environment.
The technical flaw manifests in how the browser handles resource: URLs, which are designed to reference internal browser resources rather than external web content. When Firefox fails to properly restrict these URLs, it creates a pathway for malicious actors to access privileged browser components through crafted resource: URLs. The exploitation technique leverages the PDF.js library, which is integrated into Firefox to handle PDF document rendering, demonstrating how legitimate browser features can be abused to undermine security boundaries. This particular implementation flaw allows attackers to bypass security restrictions that normally prevent web pages from accessing internal browser functionality, effectively granting them elevated privileges that should be restricted to the browser's own internal processes.
The operational impact of CVE-2015-0816 is severe and multifaceted, as it enables attackers to perform actions that would normally be impossible from a regular web page context. With chrome privileges, successful exploitation could allow attackers to read and modify browser internals, access user data, manipulate browser settings, and potentially exfiltrate sensitive information. The vulnerability essentially creates a backdoor into the browser's most privileged execution environment, making it a prime target for advanced persistent threats and sophisticated attack campaigns. Users who are running vulnerable versions of Firefox or Thunderbird are at significant risk, as the attack can be executed remotely without requiring any user interaction beyond visiting a malicious website or opening a specially crafted email attachment.
This vulnerability aligns with CWE-264, which describes permissions, privileges, and access controls issues, and maps to several ATT&CK techniques including T1059 for command and script injection and T1071 for application layer protocol usage. The flaw demonstrates how improper resource handling can lead to privilege escalation within browser environments, and represents a classic example of how security boundaries can be circumvented through flawed URL handling mechanisms. Organizations should prioritize immediate patching of affected versions and consider implementing network-level protections such as web application firewalls and content filtering solutions to mitigate the risk while waiting for full deployment of security updates. The incident underscores the critical importance of maintaining up-to-date browser software and demonstrates how seemingly minor implementation flaws in security mechanisms can have far-reaching consequences for user security and privacy.