CVE-2002-2013 in Netscape
Summary
by MITRE
Mozilla 0.9.6 and earlier and Netscape 6.2 and earlier allows remote attackers to steal cookies from another domain via a link with a hex-encoded null character (%00) followed by the target domain.
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Analysis
by VulDB Data Team • 04/19/2019
This vulnerability exists in early versions of Mozilla browsers including version 0.9.6 and earlier, as well as Netscape 6.2 and earlier web browsers. The flaw stems from improper handling of null characters within URL parsing mechanisms, specifically when processing hex-encoded null characters represented as %00. When a malicious attacker constructs a link containing a hex-encoded null character followed by a target domain, the browser fails to properly terminate the URL string at the null character, instead continuing to process the subsequent domain information. This creates a path traversal condition that allows unauthorized cookie access across domain boundaries.
The technical implementation of this vulnerability exploits a fundamental flaw in how these browsers handle URL normalization and string parsing. When a URL containing %00 is processed, the null character should act as a string terminator according to standard URL parsing rules, but these browsers fail to implement this correctly. The null character effectively truncates the URL path in the browser's internal processing, but the domain component remains accessible to the browser's cookie management system. This allows an attacker to craft malicious links that appear to target one domain but actually cause the browser to send cookies from another domain, effectively bypassing the same-origin policy that normally protects cookie isolation between different domains.
The operational impact of this vulnerability extends beyond simple cookie theft to potentially enable session hijacking and cross-site request forgery attacks. An attacker could construct a malicious webpage containing a link with a hex-encoded null character that points to a victim's banking or email domain, causing the victim's browser to send their authentication cookies from that domain to the attacker's server. This represents a significant breach of web security principles and violates the fundamental isolation guarantees that web browsers provide between different origins. The vulnerability particularly affects users of older browser versions that have not received security updates, making it a persistent threat in environments where legacy systems are still in use.
The vulnerability aligns with CWE-129 and CWE-170 which address improper handling of input validation and string handling with null characters. From an attacker's perspective, this flaw maps to techniques described in the ATT&CK framework under T1566 for credential access through phishing and T1071 for application layer protocol usage. The attack vector leverages the browser's URL parsing implementation rather than network-level vulnerabilities, making it particularly insidious as it exploits the trust relationship between the browser and web applications. Organizations should immediately upgrade affected browser versions and implement network-level protections such as content security policies and proper cookie security attributes including HttpOnly and Secure flags to mitigate the risk of exploitation.
The remediation approach requires immediate browser version updates to patched versions that properly handle null character termination in URL parsing. Security patches should address the underlying string processing logic in the browser's URL parser to ensure that null characters properly terminate URL components according to web standards. Additionally, web application developers should implement proper cookie security attributes and monitor for suspicious URL patterns that might indicate attempts to exploit this vulnerability. Network security controls including web application firewalls and URL filtering systems should be configured to detect and block requests containing hex-encoded null characters in URLs. This vulnerability demonstrates the critical importance of proper input validation and the potential for seemingly minor parsing flaws to create significant security vulnerabilities in web browsers.