CVE-2018-5133 in Firefox
Summary
by MITRE
If the "app.support.baseURL" preference is changed by a malicious local program to contain HTML and script content, this content is not sanitized. It will be executed if a user loads "chrome://browser/content/preferences/in-content/preferences.xul" directly in a tab and executes a search. This stored preference is also executed whenever an EME video player plugin displays a CDM-disabled message as a notification message. This vulnerability affects Firefox < 59.
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Analysis
by VulDB Data Team • 02/05/2021
The vulnerability identified as CVE-2018-5133 represents a critical cross-site scripting flaw in Mozilla Firefox browsers version 59 and earlier, categorized under CWE-79 Improper Neutralization of Input During Web Page Generation. This vulnerability stems from insufficient sanitization of user-controllable preferences within the browser's configuration system, specifically affecting the "app.support.baseURL" preference that controls support URL redirection. The flaw allows malicious local programs to inject HTML and script content into this preference field, creating a persistent security risk that can be exploited through multiple attack vectors. The vulnerability operates at the intersection of browser preference management and web content execution, demonstrating how seemingly benign configuration settings can become attack vectors when proper input validation is absent.
The technical exploitation of this vulnerability occurs through a sophisticated attack chain that begins with local privilege escalation or persistence mechanisms. A malicious program must first gain the ability to modify Firefox preferences, which typically requires local system access or exploitation of other vulnerabilities. Once the "app.support.baseURL" preference is modified to contain malicious HTML and script content, the vulnerability manifests when users navigate to chrome://browser/content/preferences/in-content/preferences.xul or when EME video player plugins display CDM-disabled notifications. The execution context of this vulnerability is particularly dangerous because it operates within Firefox's privileged chrome:// protocol namespace, which has elevated permissions and can access sensitive browser functionality. This attack vector is further amplified by the fact that the malicious content is stored persistently in the browser's configuration, ensuring that the payload executes every time the affected conditions are met.
The operational impact of CVE-2018-5133 extends beyond simple code execution to encompass potential data theft, browser compromise, and lateral movement within compromised systems. When users encounter CDM-disabled notifications from EME video players, the malicious content executes automatically without user interaction, creating a stealthy attack mechanism that can persist across browser sessions. This vulnerability is particularly concerning in enterprise environments where users may have elevated privileges or access to sensitive information, as it can enable attackers to harvest browser data, manipulate browser behavior, or establish persistent backdoors. The attack surface is broadened by the fact that the vulnerability affects not just user-initiated browsing but also automated browser notifications, making it difficult for users to avoid exposure. The vulnerability's persistence mechanism ensures that even after browser restarts, the malicious payload continues to execute, creating a long-term threat that can be exploited repeatedly without additional user interaction.
Mitigation strategies for CVE-2018-5133 must address both immediate remediation and long-term security posture improvements. The primary solution involves upgrading to Firefox version 59 or later, where the vulnerability has been patched through enhanced input sanitization and validation of preference values. Organizations should implement strict access controls and privilege separation to prevent local programs from modifying browser preferences, leveraging operating system security features such as file permissions, access control lists, and application whitelisting. Security monitoring should include detection of unusual changes to browser configuration files and preference modifications, particularly those involving the app.support.baseURL parameter. Network-based detection measures can monitor for suspicious URL patterns in browser traffic that might indicate exploitation attempts. Additionally, user education regarding the dangers of visiting suspicious URLs and the importance of keeping browsers updated remains crucial. The vulnerability aligns with ATT&CK technique T1059.007 Command and Scripting Interpreter: JavaScript, as it enables JavaScript execution through manipulated browser preferences, and T1068 Remote Services, as it can be exploited through browser-based attack vectors that leverage local system access for privilege escalation. Organizations should also consider implementing browser hardening measures such as disabling unnecessary chrome:// protocol access and restricting plugin execution to further reduce the attack surface.