CVE-2003-0513 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer allows remote attackers to bypass intended cookie access restrictions on a web application via "%2e%2e" (encoded dot dot) directory traversal sequences in a URL, which causes Internet Explorer to send the cookie outside the specified URL subsets, e.g. to a vulnerable application that runs on the same server as the target application.
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Analysis
by VulDB Data Team • 03/09/2021
This vulnerability represents a critical directory traversal flaw in Microsoft Internet Explorer that enables remote attackers to circumvent cookie access controls through specially crafted URL sequences. The vulnerability specifically exploits the browser's handling of encoded directory traversal sequences, where "%2e%2e" (representing the encoded form of "..") can be used to manipulate how cookies are transmitted between web applications. When Internet Explorer processes these sequences, it fails to properly enforce the intended scope restrictions that should prevent cookies from being sent outside their designated URL subsets, creating a security boundary violation that can lead to unauthorized access to sensitive information.
The technical implementation of this vulnerability stems from Internet Explorer's insufficient validation of URL path components during cookie transmission processes. When a user navigates to a URL containing encoded dot dot sequences, the browser's URL parsing mechanism incorrectly interprets these sequences, allowing the cookie data to be sent to unintended destinations on the same server. This behavior violates fundamental web security principles where cookies should only be transmitted to URLs within their specified domain and path scope. The vulnerability operates at the application layer and can be exploited through crafted web pages or malicious links that direct users to specifically constructed URLs.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable attackers to access applications that should be logically separated by cookie access controls. When multiple web applications run on the same server but require different cookie scopes, an attacker can leverage this flaw to access resources that should be protected from cross-application cookie leakage. This can result in unauthorized access to user sessions, sensitive data exposure, and potential privilege escalation within web applications that rely on proper cookie scoping for security boundaries. The vulnerability particularly affects scenarios where applications share the same server but require distinct security contexts.
This vulnerability aligns with CWE-22 Directory Traversal and CWE-345 Insufficient Verification of Data Authenticity, representing a classic case where insufficient input validation leads to security boundary violations. From an ATT&CK perspective, this maps to T1190 Exploit Public-Facing Application and T1566 Phishing, as attackers can craft malicious web content to exploit this weakness. The vulnerability demonstrates how browser implementation flaws can undermine application-level security controls, particularly cookie-based access restrictions. Organizations should implement proper URL validation mechanisms and ensure that web applications enforce strict cookie scope controls regardless of browser implementation details. The recommended mitigations include upgrading to patched versions of Internet Explorer, implementing proper server-side cookie validation, and configuring web applications to use more restrictive cookie attributes such as SameSite and Secure flags to prevent unauthorized cross-application cookie leakage.
The broader implications of this vulnerability highlight the importance of robust URL parsing and validation in web browsers and applications. It demonstrates how seemingly minor implementation details in URL handling can create significant security risks when combined with cookie management systems. This vulnerability underscores the need for comprehensive security testing of web applications and browser interactions, particularly in environments where multiple applications share the same server infrastructure. The flaw also emphasizes the critical importance of following security best practices such as implementing proper cookie scope restrictions and validating all user-supplied input to prevent directory traversal attacks and similar path manipulation exploits that can compromise application security boundaries.