CVE-2017-8504 in Edge
Summary
by MITRE
Microsoft Edge in Windows 10 1607 and 1703, and Windows Server 2016 allows an attacker to read the URL of a cross-origin request when the Microsoft Edge Fetch API incorrectly handles a filtered response type, aka "Microsoft Edge Information Disclosure Vulnerability". This CVE ID is unique from CVE-2017-8498.
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Analysis
by VulDB Data Team • 10/18/2019
The vulnerability identified as CVE-2017-8504 represents a critical information disclosure flaw in Microsoft Edge browser that affects Windows 10 versions 1607 and 1703, as well as Windows Server 2016. This security issue stems from improper handling of cross-origin requests through the Fetch API implementation, creating a scenario where sensitive URL information can be accessed by unauthorized parties. The vulnerability specifically manifests when Microsoft Edge incorrectly processes filtered response types, allowing attackers to potentially discover the target URLs of cross-origin requests that should remain hidden due to browser security policies. This flaw directly impacts the fundamental security principle of cross-origin resource sharing and demonstrates a failure in the browser's security model for handling cross-domain requests.
The technical implementation of this vulnerability resides in how Microsoft Edge processes the Fetch API when dealing with cross-origin requests that involve filtered response types. The browser's security mechanisms fail to properly sanitize or restrict access to URL information when processing these specific request scenarios, creating a pathway for information leakage. This behavior violates the same-origin policy that browsers enforce to prevent unauthorized access to resources across different domains, effectively undermining the security boundaries that protect users from potential reconnaissance attacks. The flaw operates at the application layer and specifically affects the browser's handling of HTTP response filtering mechanisms within the Fetch API implementation, making it particularly dangerous as it can be exploited through standard web browsing activities without requiring special privileges or elevated access.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable sophisticated reconnaissance attacks that allow adversaries to map network resources and identify potentially sensitive targets. Attackers can leverage this vulnerability to discover the URLs of cross-origin requests, which may reveal internal network structures, application endpoints, or sensitive resource locations that should remain hidden. This information can serve as a foundation for more advanced attacks, including targeted exploitation of specific services or endpoints that were previously unknown to the attacker. The vulnerability's presence in widely deployed Windows 10 versions and Server 2016 systems amplifies its potential impact, as it affects a large user base that may be unknowingly exposed to this information disclosure threat. Security professionals should consider this vulnerability as a potential indicator of broader security weaknesses in browser-based applications and cross-origin request handling mechanisms.
Mitigation strategies for CVE-2017-8504 should focus on immediate patch deployment through Microsoft's security updates, as the vendor has provided specific fixes for this vulnerability. Organizations should prioritize updating their systems to the latest security patches, particularly given the vulnerability's impact on core browser security mechanisms. Network administrators should implement additional monitoring for suspicious cross-origin request patterns and consider deploying web application firewalls that can detect and block potentially malicious use of this vulnerability. The mitigation approach should align with security frameworks such as those outlined in the CWE-200 standard for information exposure, emphasizing the need for proper input validation and access control mechanisms. Additionally, organizations should review their browser security policies and consider implementing additional security measures such as content security policies and strict header configurations to limit the potential impact of similar vulnerabilities. This vulnerability highlights the importance of continuous security testing and validation of browser security features, particularly in relation to cross-origin resource handling and information flow control mechanisms.