CVE-2018-6091 in Chrome
Summary
by MITRE
Service Workers can intercept any request made by an <embed> or <object> tag in Fetch API in Google Chrome prior to 66.0.3359.117 allowed a remote attacker to leak cross-origin data via a crafted HTML page.
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Analysis
by VulDB Data Team • 06/23/2023
The vulnerability identified as CVE-2018-6091 represents a critical security flaw in Google Chrome's implementation of service workers and the Fetch API that enabled unauthorized data leakage across origin boundaries. This issue specifically affected Chrome versions prior to 66.0.3359.117, where service workers could intercept requests initiated by embed and object HTML tags through the Fetch API mechanism. The flaw exploited the lack of proper cross-origin request validation within the service worker interception framework, creating a pathway for malicious actors to bypass security restrictions that normally prevent cross-origin data access.
The technical implementation of this vulnerability stems from how Chrome's service worker architecture handled requests originating from embedded content elements. When an HTML page contained embed or object tags that initiated network requests, these requests would pass through the Fetch API and could be intercepted by active service workers. The service worker implementation failed to properly enforce cross-origin security policies, allowing an attacker's service worker to capture and potentially exfiltrate sensitive data from different origins that were normally protected by the same-origin policy. This represents a violation of fundamental web security principles and constitutes a bypass of the browser's security model designed to isolate different origins from each other.
The operational impact of this vulnerability extends beyond simple data leakage, as it enabled sophisticated cross-origin attacks that could potentially access confidential information, user credentials, or sensitive application data. Attackers could craft malicious HTML pages that would load embedded content from target origins, then use service workers to intercept and capture the responses. This capability aligns with ATT&CK technique T1071.004 for application layer protocol and T1566 for credential harvesting, as it provides a method for extracting information that would normally be protected. The vulnerability could be particularly dangerous in environments where users might encounter malicious content through social engineering or compromised websites, as it operates at the browser level without requiring additional privileges or user interaction beyond visiting the malicious page.
Mitigation strategies for this vulnerability centered on updating Chrome to version 66.0.3359.117 or later, which implemented proper cross-origin request validation within the service worker interception mechanism. Security researchers recommended that organizations monitor for and deploy these updates promptly, as the vulnerability could be exploited in the wild without user interaction. Additional defensive measures included implementing proper content security policies and ensuring that service workers were properly configured to avoid unnecessary interception of cross-origin requests. The fix addressed the underlying CWE-200 vulnerability category related to information exposure and helped prevent the exploitation patterns associated with cross-origin resource sharing violations. Organizations should also consider implementing web application firewalls and monitoring for unusual cross-origin requests that might indicate exploitation attempts, while maintaining awareness of the broader attack surface that service workers create in modern web applications.