CVE-2017-7842 in Firefox
Summary
by MITRE
If a document's Referrer Policy attribute is set to "no-referrer" sometimes two network requests are made for "<link>" elements instead of one. One of these requests includes the referrer instead of respecting the set policy to not include a referrer on requests. This vulnerability affects Firefox < 57.
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Analysis
by VulDB Data Team • 03/22/2023
This vulnerability in Firefox versions prior to 57 demonstrates a critical flaw in the browser's implementation of the Referrer Policy specification, specifically affecting how the browser handles link elements with the "no-referrer" policy setting. The issue manifests when processing document elements that utilize the <link> tag with the referrer policy attribute set to "no-referrer", resulting in inconsistent network request behavior that undermines the security controls intended to protect user privacy.
The technical flaw stems from Firefox's improper handling of HTTP referer headers when making network requests for linked resources. When a document specifies a referrer policy of "no-referrer" for its link elements, the browser should suppress the inclusion of referer information in all outgoing requests. However, the vulnerability causes the browser to make two separate network requests for the same link element, with one request containing the referrer header despite the policy explicitly prohibiting such inclusion. This behavior represents a violation of the Referrer Policy specification and creates a potential privacy leak that could expose user navigation patterns to third-party servers.
The operational impact of this vulnerability extends beyond simple privacy concerns to potentially compromise user security in scenarios where sensitive information might be inadvertently exposed through referer headers. Attackers could exploit this inconsistency to gather information about user browsing behavior, potentially linking user activities across different domains or extracting sensitive data that should remain private. The vulnerability affects all Firefox versions before 57, representing a significant security gap that could be exploited in various attack scenarios involving cross-site tracking or information disclosure.
This issue aligns with CWE-200, which addresses improper exposure of sensitive information, and demonstrates a failure in proper implementation of web security policies. The vulnerability also relates to ATT&CK technique T1566, which involves social engineering through web-based attacks, as the flawed referrer handling could enable more sophisticated tracking mechanisms. Organizations using affected Firefox versions should prioritize immediate patching to ensure proper enforcement of referrer policies and prevent potential privacy leaks. The fix implemented in Firefox 57 addresses the core issue by ensuring that when "no-referrer" policy is specified, all network requests for link elements properly respect this setting without making redundant requests that could inadvertently expose referer information.
The vulnerability highlights the importance of rigorous testing of security policy implementations in web browsers, particularly around privacy controls that are fundamental to user protection. Proper enforcement of referrer policies requires careful handling of HTTP headers and network request management, where the presence of multiple requests for the same resource creates opportunities for security violations. This case demonstrates how seemingly minor implementation details in browser security features can create significant privacy risks when not properly validated against established security standards and specifications.