CVE-2017-5120 in Chrome
Summary
by MITRE
Inappropriate use of www mismatch redirects in browser navigation in Google Chrome prior to 61.0.3163.79 for Mac, Windows, and Linux, and 61.0.3163.81 for Android, allowed a remote attacker to potentially downgrade HTTPS requests to HTTP via a crafted HTML page. In other words, Chrome could transmit cleartext even though the user had entered an https URL, because of a misdesigned workaround for cases where the domain name in a URL almost matches the domain name in an X.509 server certificate (but differs in the initial "www." substring).
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Analysis
by VulDB Data Team • 01/11/2021
The vulnerability described in CVE-2017-5120 represents a critical security flaw in Google Chrome's handling of HTTPS to HTTP downgrade attacks, specifically targeting the browser's navigation logic and certificate validation mechanisms. This issue affects Chrome versions prior to 61.0.3163.79 on Mac, Windows, and Linux platforms, as well as version 61.0.3163.81 on Android devices, demonstrating the widespread nature of the flaw across multiple operating systems and device types. The vulnerability stems from an improper implementation of redirect handling when domain names in URLs differ only by the presence or absence of the "www." prefix, creating a potential attack vector that undermines the fundamental security guarantees of HTTPS encryption.
The technical flaw manifests in Chrome's approach to handling cases where an X.509 server certificate contains a domain name that is nearly identical to the requested URL but differs only in the initial "www." substring. This misimplementation creates a scenario where the browser's navigation logic incorrectly processes these domain mismatches, allowing attackers to exploit the redirect mechanism to downgrade secure HTTPS connections to insecure HTTP transmissions. The vulnerability specifically targets the browser's workaround for handling such near-matching domain names, where Chrome should have maintained the secure HTTPS protocol but instead permitted cleartext transmission when processing crafted HTML pages containing malicious redirects.
The operational impact of this vulnerability is severe and potentially devastating for users, as it enables man-in-the-middle attackers to intercept and modify sensitive data transmitted over what users believe to be secure connections. When users navigate to an HTTPS URL that should be protected by encryption, the browser may unknowingly transmit the same data over HTTP, exposing credentials, personal information, and other sensitive content to network-based attackers. This downgrade attack can occur without user awareness, as the browser's flawed redirect logic allows the transition from secure to insecure protocols without proper validation or warning mechanisms. The attack vector through crafted HTML pages means that users can be compromised simply by visiting malicious websites that contain carefully constructed redirect code.
This vulnerability aligns with CWE-310, which addresses cryptographic issues related to weak or improperly implemented cryptographic protocols, specifically highlighting the failure to maintain secure communication channels during navigation. The flaw also corresponds to ATT&CK technique T1071.004, which covers application layer protocol usage for command and control communications, as the downgrade mechanism enables attackers to establish insecure communication channels that can be leveraged for further exploitation. The security implications extend beyond simple data interception to potentially enable more sophisticated attacks such as credential theft, session hijacking, and data manipulation. Organizations and users must understand that this vulnerability represents a fundamental failure in Chrome's security model, where the browser's attempt to provide user-friendly navigation by automatically handling domain variations inadvertently creates a security weakness that can be exploited by threat actors. The fix implemented in Chrome versions 61.0.3163.79 and 61.0.3163.81 addressed the redirect handling logic to properly maintain HTTPS security boundaries and prevent the inappropriate downgrade of secure connections to insecure HTTP transmissions.