CVE-2006-6971 in Firefox
Summary
by MITRE
Mozilla Firefox 2.0, possibly only when running on Windows, allows remote attackers to bypass the Phishing Protection mechanism by representing an IP address in (1) dotted-hex, (2) dotted-octal, (3) single decimal integer, (4) single hex integer, or (5) single octal integer format, which is not captured by the blacklist filter.
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Analysis
by VulDB Data Team • 08/19/2018
The vulnerability described in CVE-2006-6971 represents a significant security flaw in Mozilla Firefox 2.0's phishing protection mechanism, specifically affecting systems running on Windows operating systems. This issue exploits the browser's handling of IP address representations in web requests, creating a bypass opportunity for malicious actors seeking to evade detection by Firefox's built-in anti-phishing measures. The vulnerability stems from the browser's inability to properly recognize and filter IP addresses when they are encoded in various non-standard numeric formats, which can be used to disguise malicious domains and bypass the phishing protection blacklist.
The technical flaw manifests when Firefox encounters IP addresses represented in alternative numeric formats such as dotted-hexadecimal, dotted-octal, single decimal integers, single hexadecimal integers, or single octal integers. These representations, while mathematically equivalent to standard dotted-decimal notation, are not properly accounted for in the browser's phishing protection filtering logic. The vulnerability specifically affects the way Firefox processes and validates IP address formats during web navigation, allowing attackers to craft URLs that appear legitimate to the browser's security mechanisms while actually pointing to malicious destinations. This represents a classic case of input validation bypass where the application fails to normalize or properly interpret alternative representations of the same data.
From an operational perspective, this vulnerability creates a substantial risk for Firefox users who rely on the browser's phishing protection features for security. Attackers can exploit this weakness by crafting phishing URLs that use alternative IP address formats to bypass the blacklist filters, potentially leading to successful phishing attacks against unsuspecting users. The impact is particularly concerning because it undermines the fundamental security assumption that IP address-based blacklists can effectively protect users from known malicious sites. The vulnerability essentially allows attackers to perform a form of address obfuscation that defeats the browser's built-in security protections, potentially leading to credential theft, malware distribution, or other malicious activities. This represents a critical failure in the browser's security architecture and demonstrates the importance of comprehensive input validation in security-sensitive applications.
The vulnerability can be classified under CWE-20 as "Improper Input Validation," which is a fundamental weakness in software security that occurs when applications fail to properly validate or sanitize input data. This flaw also relates to ATT&CK technique T1071.004, which involves application layer protocol manipulation, specifically targeting web browser security mechanisms. Organizations and users should consider this vulnerability as part of a broader security posture assessment, particularly when evaluating browser security features and the effectiveness of web-based protection mechanisms. The issue highlights the importance of implementing robust normalization and validation procedures for all input data, especially in security-critical contexts where alternative representations of the same data could be used to bypass protections. Mitigation strategies should include immediate patching of affected Firefox versions, implementation of additional network-level security controls, and enhanced user education regarding phishing detection techniques. The vulnerability underscores the need for security mechanisms to account for all possible valid representations of data rather than relying on single, specific formats for detection and filtering purposes.