CVE-2018-5117 in Firefox
Summary
by MITRE
If right-to-left text is used in the addressbar with left-to-right alignment, it is possible in some circumstances to scroll this text to spoof the displayed URL. This issue could result in the wrong URL being displayed as a location, which can mislead users to believe they are on a different site than the one loaded. This vulnerability affects Thunderbird < 52.6, Firefox ESR < 52.6, and Firefox < 58.
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Analysis
by VulDB Data Team • 11/26/2025
This vulnerability represents a sophisticated text rendering issue that exploits the bidirectional text handling capabilities of web browsers to create misleading user interface elements. The flaw specifically occurs when right-to-left text is processed within the address bar while maintaining left-to-right alignment, creating a scenario where text can be manipulated to obscure or distort the actual URL being displayed. This type of vulnerability falls under the category of user interface spoofing attacks that leverage the complex interactions between text directionality and visual presentation. The issue stems from how browsers handle Unicode bidirectional algorithm processing, particularly when combining right-to-left scripts with left-to-right display contexts. According to CWE-1274, this vulnerability is classified as a text processing flaw that can lead to user deception through manipulated visual presentation. The vulnerability affects major browser implementations including Thunderbird email client and various Firefox versions, indicating a widespread impact across different software platforms that rely on similar text rendering engines.
The technical implementation of this vulnerability exploits the Unicode bidirectional text algorithm to create visual deception in the address bar display. When right-to-left text is embedded within left-to-right aligned contexts, the browser's rendering engine can potentially misalign or manipulate the visual presentation of the URL string. This manipulation allows attackers to position text elements in ways that obscure the true origin of a web page or make it appear as though the browser is pointing to a different domain than the actual loaded content. The flaw specifically manifests when browsers process mixed-direction text within the address bar context, creating a scenario where the visual representation of the URL does not match the underlying resource being accessed. The vulnerability's effectiveness depends on the specific text patterns used and the browser's implementation of the Unicode bidirectional algorithm, which is standardized under the Unicode Consortium specifications and can be mapped to ATT&CK technique T1059.001 for user interface manipulation through text processing.
The operational impact of this vulnerability extends beyond simple phishing attempts to encompass broader security implications for user trust and browser security assurances. Users who encounter this vulnerability may be misled into believing they are visiting legitimate websites when they are actually accessing malicious content, potentially leading to credential theft, data compromise, or other security breaches. The vulnerability creates a false sense of security by displaying misleading URLs that appear to be from trusted domains, making it particularly dangerous for users who rely on visual URL verification for security decisions. This type of deception can be particularly effective in social engineering attacks where attackers exploit user familiarity with browser interfaces and their expectations about URL display consistency. The vulnerability affects not just individual users but also enterprise security models that depend on accurate URL representation for access control and security monitoring purposes. Organizations implementing security policies that rely on URL-based access controls or user verification mechanisms may experience significant security gaps when this vulnerability is present in their browser environments.
Mitigation strategies for this vulnerability require both immediate software updates and enhanced user awareness practices. The most effective immediate solution involves updating affected browsers to versions that properly handle bidirectional text rendering without creating display manipulation opportunities. Security patches for Firefox ESR 52.6, Firefox 58, and Thunderbird 52.6 addressed the underlying text processing algorithms to prevent the specific scenarios that enabled this vulnerability. Organizations should implement comprehensive patch management processes to ensure all affected systems receive updates promptly. Additionally, browser security teams should consider implementing additional safeguards such as enhanced URL validation routines that can detect and flag potentially manipulated address bar content. User education remains critical as security awareness programs should emphasize that URL verification should not rely solely on visual appearance but should also include checking for proper SSL certificates and domain verification. The vulnerability's resolution demonstrates the importance of thorough testing of text rendering and internationalization features in security-critical applications, aligning with industry best practices for secure software development. Security monitoring systems should be enhanced to detect unusual patterns in address bar rendering that might indicate attempts to exploit this vulnerability, particularly in environments where users frequently access international content with mixed text directions.