CVE-2003-1561 in Web Browser
Summary
by MITRE
Opera, probably before 7.50, sends Referer headers containing https:// URLs in requests for http:// URLs, which allows remote attackers to obtain potentially sensitive information by reading Referer log data.
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Analysis
by VulDB Data Team • 04/22/2019
The vulnerability described in CVE-2003-1561 represents a significant information disclosure issue within the Opera web browser implementation of referer header handling. This flaw existed in Opera versions prior to 7.50 and demonstrates a critical gap in how the browser manages cross-protocol referer information. The vulnerability specifically affects the manner in which Opera constructs referer headers when navigating from secure https:// URLs to non-secure http:// URLs, creating an unexpected information leakage mechanism that could be exploited by remote attackers.
The technical implementation of this vulnerability stems from Opera's incorrect handling of referer headers during protocol transitions. When a user navigates from a secure https:// page to an insecure http:// page, the browser should ideally either omit the referer header entirely or strip sensitive information from it. However, Opera's implementation failed to properly sanitize the referer header, causing it to retain the full https:// URL including any sensitive parameters or session identifiers. This behavior violates the expected security boundaries between secure and non-secure contexts, creating a scenario where potentially sensitive information flows from secure to non-secure environments.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates opportunities for attackers to harvest sensitive data through various means. Attackers can exploit this flaw by setting up malicious http:// servers that log referer information, allowing them to capture session tokens, user credentials, or other confidential data that was previously transmitted within the https:// context. This vulnerability directly relates to CWE-200, which describes the improper exposure of sensitive information, and represents a classic case of information leakage through protocol boundary violations. The attack vector operates through the standard referer header mechanism that web servers and applications use to track user navigation paths, making it particularly insidious as it leverages legitimate browser functionality for malicious purposes.
From an attacker perspective, this vulnerability aligns with techniques described in the attack pattern taxonomy under the MITRE ATT&CK framework, specifically relating to credential access and information discovery phases. The flaw enables adversaries to perform passive reconnaissance and data harvesting without requiring active exploitation or direct injection attacks. Organizations and users who relied on Opera for browsing activities were exposed to potential session hijacking, credential theft, and sensitive data exposure when navigating between secure and non-secure web environments. The vulnerability demonstrates the importance of proper protocol handling and the need for comprehensive security testing across all browser functionalities, particularly those involving cross-protocol communications and header management. The fix for this issue required Opera to implement proper referer header sanitization that would strip or modify the referer information when transitioning from secure to non-secure contexts, ensuring that sensitive information would not be inadvertently exposed through the referer header mechanism.