CVE-2018-5138 in Firefox
Summary
by MITRE
A spoofing vulnerability can occur when a malicious site with an extremely long domain name is opened in an Android Custom Tab (a browser panel inside another app) and the default browser is Firefox for Android. This could allow an attacker to spoof which page is actually loaded and in use. Note: this issue only affects Firefox for Android. Other versions and operating systems are unaffected. This vulnerability affects Firefox < 59.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 02/05/2021
This vulnerability represents a sophisticated spoofing attack vector that exploits the handling of extremely long domain names within Android Custom Tabs functionality. The flaw specifically manifests when a malicious website with an excessively long domain name is opened through an Android Custom Tab interface while Firefox for Android serves as the default browser. The vulnerability stems from the browser's inability to properly truncate or handle domain names that exceed normal length parameters, creating a window where attackers can manipulate the displayed URL to appear as a legitimate website while actually loading malicious content. This issue falls under the category of user interface deception and represents a significant threat to user trust and security in mobile browsing environments.
The technical implementation of this vulnerability exploits the way Firefox for Android processes and displays domain names within the Custom Tab interface. When a domain name exceeds normal length thresholds, the browser's URL display mechanism fails to properly truncate or handle the excessively long string, allowing the malicious site to present a deceptive URL that appears legitimate to users. This behavior creates a scenario where users cannot distinguish between the actual site being loaded and a spoofed version, potentially leading to phishing attacks or other malicious activities. The vulnerability demonstrates poor input validation and inadequate string handling mechanisms within the browser's UI rendering components, which is classified as a CWE-129 weakness related to insufficient input length validation.
The operational impact of this vulnerability extends beyond simple deception to potentially enable more serious security breaches including credential theft, malware delivery, and financial fraud. Users interacting with the affected browser may unknowingly navigate to malicious sites while believing they are on legitimate websites, creating a false sense of security that attackers can exploit. The attack surface is particularly concerning in mobile environments where users may be less vigilant about URL verification due to the smaller screen sizes and different browsing patterns compared to desktop environments. This vulnerability aligns with ATT&CK technique T1531 which involves the manipulation of browser interfaces to deceive users into performing unintended actions.
Mitigation strategies for this vulnerability focus on both immediate remediation and long-term architectural improvements. The primary solution involves updating Firefox for Android to version 59 or later, where the underlying string handling and URL display mechanisms have been patched to properly manage excessively long domain names. Organizations should implement comprehensive browser update policies to ensure all mobile devices running Firefox for Android receive the necessary security patches promptly. Additionally, security teams should consider implementing network-level monitoring to detect and alert on suspiciously long domain names being accessed through Custom Tab interfaces, providing an additional layer of defense against exploitation attempts. The vulnerability also underscores the importance of proper input validation and the need for security-conscious development practices in mobile browser applications.