CVE-2009-3049 in Web Browser
Summary
by MITRE
Opera before 10.00 does not properly display all characters in Internationalized Domain Names (IDN) in the address bar, which allows remote attackers to spoof URLs and conduct phishing attacks, related to Unicode and Punycode.
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Analysis
by VulDB Data Team • 03/08/2025
The vulnerability described in CVE-2009-3049 represents a critical security flaw in Opera web browsers prior to version 10.00 that stems from inadequate handling of Internationalized Domain Names in the address bar display. This issue fundamentally compromises the browser's ability to accurately represent domain names that contain non-ASCII characters, creating a significant attack surface for malicious actors seeking to exploit user trust in web navigation. The flaw specifically manifests when the browser processes Internationalized Domain Names using Unicode and Punycode encoding standards, where the visual representation of domain names becomes misleading or deceptive to end users.
The technical root cause of this vulnerability lies in Opera's insufficient implementation of IDN display logic within its address bar component. When a user navigates to a domain containing Unicode characters, the browser should properly convert and display the domain name in a manner that accurately reflects the intended destination. However, the vulnerable version fails to consistently render all characters from IDN domains, particularly when they are encoded using Punycode standards. This incomplete rendering creates opportunities for attackers to register domain names that visually appear identical or nearly identical to legitimate domains but contain different Unicode characters that are not properly displayed in the address bar.
The operational impact of this vulnerability is severe and directly enables sophisticated phishing attacks. Attackers can register domain names that contain visually similar Unicode characters that are indistinguishable from legitimate domains when displayed in the browser's address bar. For example, a malicious actor might register a domain that appears identical to a well-known bank's website but uses Unicode characters that look the same as ASCII characters but have different code points. This creates an environment where users cannot reliably distinguish between legitimate and malicious websites based on address bar display alone, making it extremely difficult to detect fraudulent sites. The vulnerability specifically relates to CWE-20, which addresses improper input validation, and falls under the broader category of CWE-1004, concerning security-relevant CWE entries.
The security implications extend beyond simple phishing attempts to encompass broader trust model violations within web browsing environments. When users cannot trust the address bar display to accurately represent the destination they are visiting, the entire security architecture of web browsers becomes compromised. This vulnerability enables attackers to bypass user security awareness and trust mechanisms, as users are unable to visually verify the authenticity of websites they are visiting. The attack vector is particularly effective because it exploits the human tendency to trust visual cues from familiar interfaces, making it difficult for even security-conscious users to detect malicious sites. This flaw directly corresponds to techniques described in the ATT&CK framework under T1566, which covers phishing techniques, and T1071, which encompasses application layer protocols.
Mitigation strategies for this vulnerability require immediate browser updates to versions that properly implement IDN display standards according to RFC 3490 and RFC 3492 specifications. Users should ensure their Opera browsers are updated to version 10.00 or later, which includes proper handling of Unicode and Punycode characters in address bar display. Organizations should implement additional security measures such as URL filtering and content security policies to detect and block suspicious domain registrations. Security awareness training should emphasize the importance of verifying website authenticity through multiple means beyond address bar display, including checking SSL certificates and using security tools that can identify potential IDN spoofing attempts. The vulnerability also underscores the importance of implementing proper input validation and character encoding handling in web applications and browsers to prevent similar issues in other components of the security ecosystem.