CVE-2018-6137 in Chrome
Summary
by MITRE
CSS Paint API in Blink in Google Chrome prior to 67.0.3396.62 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 CSS Paint API vulnerability identified as CVE-2018-6137 represents a critical security flaw in Google Chrome's Blink rendering engine that existed prior to version 67.0.3396.62. This vulnerability specifically targets the CSS Paint API implementation which allows web developers to programmatically generate CSS backgrounds and borders using JavaScript. The flaw enables malicious actors to construct specially crafted HTML pages that can exploit the API to access cross-origin data, effectively bypassing the same-origin policy that normally protects web applications from unauthorized data access across different domains.
The technical exploitation of this vulnerability occurs through the CSS Paint API's handling of cross-origin resources when generating visual elements. When Chrome processes CSS paint worklets that reference external resources, the implementation fails to properly validate or sanitize cross-origin data access, creating a pathway for attackers to infer information about resources loaded from different origins. This type of information leakage can include sensitive data such as image content, resource metadata, or even timing information that can be used to reconstruct cross-origin content. The vulnerability operates at the intersection of web rendering and security boundaries, where the paint API's design does not adequately account for cross-origin isolation requirements.
The operational impact of this vulnerability extends beyond simple data leakage, as it fundamentally undermines the browser's security model and can enable more sophisticated attacks. Attackers can leverage this flaw to perform cross-origin resource fingerprinting, potentially identifying specific content or user data from other domains without explicit permission. The implications are particularly severe in environments where users may be browsing multiple sensitive domains simultaneously, as the vulnerability could allow for the reconstruction of user profiles, content analysis, or even targeted attacks against specific web applications. This represents a violation of the fundamental web security principle that prevents unauthorized cross-origin data access.
Security mitigations for CVE-2018-6137 primarily involve updating to Chrome version 67.0.3396.62 or later, which includes proper validation of cross-origin data handling within the CSS Paint API implementation. Additionally, web developers should implement proper CSP (Content Security Policy) headers to restrict paint worklet execution and limit the potential attack surface. Organizations should also consider implementing browser hardening measures and monitoring for suspicious CSS paint API usage patterns. From an ATT&CK framework perspective, this vulnerability maps to techniques involving information gathering and privilege escalation through browser-based attacks, while CWE classification places it under CWE-200 for exposure of sensitive information and CWE-352 for cross-site request forgery. The vulnerability demonstrates the importance of thorough security review processes for new web APIs and highlights the need for comprehensive cross-origin security testing in browser implementations.