CVE-2005-2830 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 5.01, 5.5, and 6, when using an HTTPS proxy server that requires Basic Authentication, sends URLs in cleartext, which allows remote attackers to obtain sensitive information, aka "HTTPS Proxy Vulnerability."
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 06/29/2025
The vulnerability described in CVE-2005-2830 represents a critical security flaw in Microsoft Internet Explorer versions 5.01, 5.5, and 6 that specifically manifests when users navigate through HTTPS proxy servers requiring Basic Authentication. This issue stems from the browser's improper handling of secure communications when intermediate proxy servers are involved in the connection process. The flaw creates a significant information disclosure risk that directly contradicts the fundamental security expectations of HTTPS protocol implementation.
The technical root cause of this vulnerability lies in how Internet Explorer processes URLs when establishing connections through proxy servers that demand Basic Authentication credentials. When a user attempts to access a secure website through such a proxy, the browser fails to properly encrypt the URL portion of the request, instead transmitting it in cleartext format. This occurs because the browser incorrectly assumes that the proxy server is handling the encryption process rather than properly securing the entire communication channel. The vulnerability operates at the application layer of the OSI model and specifically affects the HTTP protocol implementation within the browser's networking stack.
The operational impact of this vulnerability is severe and multifaceted, creating multiple attack vectors for remote adversaries. Attackers positioned within the network path between the user and the target server can intercept and decode the cleartext URLs, gaining access to sensitive information including login credentials, session identifiers, and potentially confidential data transmitted through the browser. This vulnerability directly violates the principle of confidentiality in the CIA triad and exposes users to man-in-the-middle attacks. The flaw particularly affects organizations using corporate proxy servers that require Basic Authentication, making it a significant concern for enterprise environments where such configurations are common.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-312 (Cleartext Storage of Sensitive Information) and CWE-310 (Cryptographic Issues) categories, demonstrating how improper handling of authentication mechanisms can lead to information disclosure. The attack pattern corresponds to techniques documented in the MITRE ATT&CK framework under T1071.004 (Application Layer Protocol: DNS) and T1566 (Phishing) as attackers can leverage this weakness to gather intelligence for more sophisticated attacks. Organizations affected by this vulnerability face increased risk of credential theft, session hijacking, and data interception attacks that can compromise entire corporate networks.
The recommended mitigation strategies include immediate deployment of Microsoft security patches, which address the core issue by ensuring proper URL encryption when communicating through proxy servers. Network administrators should also consider implementing additional security controls such as SSL/TLS inspection capabilities, enhanced proxy server configurations that properly handle authentication, and network monitoring solutions to detect anomalous traffic patterns. Organizations should conduct thorough security assessments to identify all instances of affected Internet Explorer versions and implement mandatory browser upgrades to modern secure alternatives that properly handle HTTPS communications through proxy environments.