CVE-2026-17977 in Chrome
Summary
by MITRE • 07/30/2026
Policy bypass in CSS in Google Chrome prior to 151.0.7922.72 allowed a remote attacker to leak cross-origin data via a crafted HTML page. (Chromium security severity: Low)
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Analysis
by VulDB Data Team • 07/30/2026
This vulnerability represents a policy bypass in Google Chrome's CSS implementation that existed prior to version 151.0.7922.72, classified as a low severity issue within Chromium's security framework. The flaw specifically pertained to how Chrome handled cross-origin resource access through Cascading Style Sheets, creating an avenue for remote attackers to potentially extract sensitive data from different origins. The vulnerability exploited weaknesses in the browser's same-origin policy enforcement mechanisms, which are fundamental security controls designed to prevent unauthorized access between web pages from different domains or origins.
The technical nature of this flaw involved CSS properties and selectors that were not properly validating cross-origin access restrictions when processing crafted HTML content. Attackers could construct malicious web pages that leveraged specific CSS behaviors to indirectly access or observe resources from other origins, effectively circumventing the browser's security boundaries. This type of vulnerability falls under the category of Cross-Origin Resource Sharing (CORS) policy bypasses and can be associated with CWE-284, which addresses improper access control mechanisms in web applications. The implementation likely involved CSS pseudo-elements, attribute selectors, or other styling features that could be manipulated to create information leakage paths.
The operational impact of this vulnerability was significant despite its low severity classification, as it enabled remote attackers to perform cross-origin data exfiltration without requiring user interaction or privileged access. An attacker could potentially craft a malicious website that would load content from another domain and extract sensitive information through carefully constructed CSS rules. This capability would allow for the collection of cookies, session tokens, or other confidential data that should normally be restricted by the browser's security model. The attack vector typically required the victim to navigate to the malicious page while having an active session with the target origin, making it particularly dangerous in scenarios involving authenticated browsing sessions.
Mitigation strategies for this vulnerability centered around updating to Chrome version 151.0.7922.72 or later, which contained the necessary patches to properly enforce cross-origin restrictions in CSS processing. Organizations should implement comprehensive patch management procedures to ensure all browsers are kept up-to-date with the latest security fixes. Additionally, web application developers should follow secure coding practices and regularly audit their applications for potential CSS-based information leakage vulnerabilities. The fix likely involved strengthening the validation mechanisms within Chrome's CSS parser and ensuring that all cross-origin resource access attempts through styling elements were properly validated against the browser's security policies. This vulnerability aligns with ATT&CK technique T1566, which covers social engineering tactics including the use of malicious web content to exploit browser vulnerabilities for data exfiltration purposes.
The broader implications of such vulnerabilities highlight the complexity of modern web browser security models and the challenges in maintaining robust cross-origin policy enforcement across diverse CSS features. Browser vendors must continuously monitor and update their implementations to address emerging attack vectors that can bypass fundamental security controls, particularly those involving styling and presentation layer components that are often overlooked in traditional security assessments. This incident demonstrates the importance of comprehensive security testing that includes not just core functionality but also edge cases within complex web technologies like CSS that form integral parts of modern web applications.