CVE-2009-1834 in Firefox
Summary
by MITRE
Visual truncation vulnerability in netwerk/dns/src/nsIDNService.cpp in Mozilla Firefox before 3.0.11 and SeaMonkey before 1.1.17 allows remote attackers to spoof the location bar via an IDN with invalid Unicode characters that are displayed as whitespace, as demonstrated by the \u115A through \u115E characters.
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Analysis
by VulDB Data Team • 12/23/2024
The vulnerability described in CVE-2009-1834 represents a sophisticated visual spoofing attack targeting the domain name system implementation within Mozilla Firefox and SeaMonkey browsers. This issue specifically affects the nsIDNService.cpp component responsible for handling internationalized domain names, creating a critical security gap that enables attackers to manipulate user perception of web addresses through carefully crafted Unicode characters. The flaw exploits the browser's rendering of internationalized domain names where certain Unicode characters are displayed as whitespace, allowing malicious actors to construct deceptive domain names that appear legitimate to users.
The technical implementation of this vulnerability stems from improper handling of Unicode characters within the IDN (Internationalized Domain Name) processing pipeline. When Firefox processes domain names containing invalid Unicode characters in the range of \u115A through \u115E, the browser's rendering engine treats these characters as whitespace rather than as actual domain name components. This creates a scenario where attackers can append invisible or whitespace characters to domain names, making them visually identical to legitimate addresses while maintaining different underlying DNS resolution paths. The vulnerability specifically targets the location bar display mechanism, which is crucial for user trust and security awareness in web browsing contexts.
The operational impact of this vulnerability extends beyond simple visual deception to create significant risks for user security and trust. Attackers can exploit this flaw to create domain names that appear identical to legitimate websites while routing users to malicious destinations, effectively enabling man-in-the-middle attacks and phishing operations. Users may be deceived into believing they are visiting trusted websites when they are actually interacting with attacker-controlled systems. This vulnerability particularly affects users who rely on visual inspection of URL bars for security verification, as the spoofed addresses appear identical to legitimate ones. The attack vector requires no special privileges or complex exploitation techniques, making it accessible to adversaries with basic knowledge of Unicode character manipulation.
Security mitigations for this vulnerability involve implementing robust input validation and sanitization of Unicode characters within the IDN processing pipeline. Browser vendors should enforce strict character validation rules that prevent the inclusion of invalid Unicode sequences in domain name parsing, ensuring that characters in the \u115A through \u115E range are properly rejected or converted to visible representations. The fix requires modifications to the nsIDNService.cpp implementation to validate Unicode character sequences before rendering domain names in the location bar. Organizations should prioritize immediate deployment of patched browser versions, as this vulnerability represents a critical risk to user security. Additionally, implementing user education about the importance of verifying SSL certificates and not relying solely on visual URL inspection can provide additional defense layers. This vulnerability aligns with CWE-176, which addresses the improper handling of whitespace characters in input validation, and maps to ATT&CK technique T1566, focusing on spearphishing with malicious attachments and links that exploit user trust through visual deception.