CVE-2018-6051 in Chrome
Summary
by MITRE
XSS Auditor in Google Chrome prior to 64.0.3282.119, did not ensure the reporting URL was in the same origin as the page it was on, which allowed a remote attacker to obtain referrer details via a crafted HTML page.
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Analysis
by VulDB Data Team • 02/03/2023
The vulnerability identified as CVE-2018-6051 represents a significant security flaw in Google Chrome's XSS Auditor implementation that existed prior to version 64.0.3282.119. This issue specifically targeted the cross-site scripting protection mechanism that Chrome employed to detect and prevent malicious script execution. The XSS Auditor was designed to monitor for potential cross-site scripting attacks and report them to designated URLs, but this particular flaw compromised the origin validation checks that should have prevented unauthorized reporting. The vulnerability exploited the lack of proper origin verification when determining whether a reporting URL could be used to transmit security-related information from a web page. Attackers could craft malicious HTML pages that would trigger the XSS Auditor to report information to a URL controlled by the attacker, bypassing the intended security boundaries that should have restricted such reporting to same-origin destinations.
The technical flaw in this vulnerability stems from insufficient input validation within the XSS Auditor component's origin checking logic. When Chrome's XSS Auditor encountered a potential cross-site scripting scenario, it would attempt to report the incident to a configured reporting URL. However, the implementation failed to properly verify that the reporting URL shared the same origin as the page triggering the alert. This oversight created an attack vector where malicious actors could manipulate the reporting mechanism to exfiltrate referrer information from users visiting compromised pages. The vulnerability specifically allowed remote attackers to obtain referrer details, which could contain sensitive information about user navigation patterns, search queries, or links to internal resources that might not be otherwise exposed. This weakness was classified under CWE-20, which encompasses improper input validation, and represented a failure in implementing proper origin validation controls that are fundamental to web security architectures.
The operational impact of CVE-2018-6051 was substantial as it enabled attackers to harvest sensitive referrer data from users who visited malicious websites. Referrer information can contain highly sensitive details including search terms, internal network paths, authentication tokens, or personal information that users might not expect to be transmitted to external domains. When users navigated from a secure or sensitive page to a maliciously crafted page, the XSS Auditor could be tricked into sending this information to attacker-controlled servers, effectively creating a data exfiltration channel. The vulnerability was particularly concerning because it exploited a security feature designed to protect users, turning it into an attack vector that could be used to gather intelligence about user behavior and system access patterns. This type of information leakage could be used for social engineering attacks, targeted phishing campaigns, or to map internal network structures and identify potential attack targets.
Mitigation strategies for CVE-2018-6051 centered on updating to Chrome version 64.0.3282.119 or later, where the origin validation logic was corrected to properly enforce same-origin restrictions for reporting URLs. Organizations should have implemented comprehensive browser update policies to ensure all users were protected against this vulnerability. Additionally, administrators could have configured Content Security Policy headers to limit the sources to which reporting information could be sent, providing an additional layer of protection. The fix implemented by Google addressed the core issue by strengthening the origin validation checks within the XSS Auditor, ensuring that reporting URLs must match the origin of the page triggering the alert. This vulnerability highlighted the importance of proper security feature implementation and the potential for legitimate security mechanisms to become attack vectors when not properly validated. The incident reinforced industry best practices around implementing security controls with proper input validation and origin checking, aligning with ATT&CK technique T1071.004 for application layer protocol: web protocols, where proper validation of web communication endpoints is critical to prevent information leakage through security features that are intended to protect rather than harm users.