CVE-2013-5593 in Firefox
Summary
by MITRE
The SELECT element implementation in Mozilla Firefox before 25.0, Firefox ESR 24.x before 24.1, Thunderbird before 24.1, and SeaMonkey before 2.22 does not properly restrict the nature or placement of HTML within a dropdown menu, which allows remote attackers to spoof the address bar or conduct clickjacking attacks via vectors that trigger navigation off of a page containing this element.
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Analysis
by VulDB Data Team • 11/25/2025
The vulnerability identified as CVE-2013-5593 represents a critical security flaw in Mozilla Firefox and related applications that affects the handling of HTML content within SELECT dropdown elements. This issue stems from insufficient validation mechanisms that govern how HTML markup is processed and rendered when dropdown menus appear in web interfaces. The flaw exists in the core rendering engine's approach to managing user interface elements, specifically where the SELECT element's dropdown functionality fails to properly sanitize or restrict the types of HTML content that can be embedded within it. Attackers can exploit this weakness by crafting malicious HTML content that gets injected into the dropdown menu structure, creating a dangerous scenario where legitimate interface elements become vectors for malicious activity.
The technical nature of this vulnerability aligns with CWE-79, which addresses Cross-Site Scripting (XSS) conditions, and specifically relates to improper neutralization of input during web page generation. The flaw allows remote attackers to inject HTML content that can manipulate the visual presentation and functional behavior of web pages, particularly when dropdown menus are involved. When a web page contains a SELECT element with maliciously crafted options, the browser's rendering engine processes this content without adequate sanitization, enabling attackers to embed HTML elements that can deceive users about the true nature of the web page they are interacting with. This includes the ability to overlay malicious content over legitimate interface elements, effectively creating deceptive user experiences that can be exploited for phishing attacks or social engineering campaigns.
The operational impact of this vulnerability extends beyond simple visual deception to encompass serious security risks including address bar spoofing and clickjacking attacks. When attackers successfully exploit this vulnerability, they can manipulate how the browser displays navigation elements, making it appear as though users are visiting a trusted domain when they are actually interacting with malicious content. The clickjacking aspect becomes particularly dangerous because users may be tricked into performing unintended actions based on the deceptive interface presented by the compromised SELECT element. This vulnerability can be particularly effective in phishing scenarios where attackers create convincing facsimiles of legitimate banking or e-commerce interfaces, potentially leading to financial fraud or data theft. The attack vectors typically involve embedding JavaScript code or malicious HTML elements within the dropdown options that can execute when users interact with the menu, bypassing traditional security mechanisms.
Organizations and users affected by this vulnerability should implement immediate mitigation strategies including updating to the patched versions of affected software, which were released as Firefox 25.0, Thunderbird 24.1, and SeaMonkey 2.22. The recommended approach involves maintaining current software versions and implementing additional security layers such as content security policies that restrict the types of HTML content that can be embedded in web interfaces. Browser security configurations should be reviewed to ensure that HTML content within dropdown menus is properly sanitized and that users are not exposed to potentially malicious content. Security teams should also consider implementing monitoring for suspicious HTML content patterns and user behavior that might indicate exploitation attempts. This vulnerability demonstrates the importance of comprehensive input validation and the need for robust sanitization mechanisms in web browser implementations, particularly for elements that can be dynamically modified by web content. The incident underscores the critical nature of regular security updates and the potential for seemingly minor UI elements to become significant attack vectors when proper security controls are not implemented.