CVE-2026-17854 in Chrome
Summary
by MITRE • 07/30/2026
Insufficient policy enforcement in WebMCP in Google Chrome prior to 151.0.7922.72 allowed a remote attacker to bypass same origin policy via a crafted HTML page. (Chromium security severity: Medium)
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Analysis
by VulDB Data Team • 07/30/2026
The vulnerability in question represents a critical weakness in Google Chrome's WebMCP implementation that existed prior to version 151.0.7922.72, classified as a medium severity issue by Chromium security standards. This flaw stems from inadequate policy enforcement mechanisms that govern how web content interacts with different origins within the browser's security model. The same origin policy serves as a fundamental security boundary in web browsers, preventing scripts from one origin from accessing resources or data from another origin without proper authorization. When this policy is weakened or bypassed, it creates significant security risks for users and applications that rely on browser-based isolation.
The technical implementation of this vulnerability allows remote attackers to craft malicious HTML pages that can circumvent the same origin policy protections through specific WebMCP configurations or implementations. WebMCP, which stands for Web Multi-Process Container, is designed to provide secure multi-process execution environments for web content while maintaining proper security boundaries between different origins. The flaw occurs when the system fails to properly validate or enforce access controls that should prevent cross-origin data leakage or unauthorized interactions between different web applications running in separate processes. This bypass enables attackers to potentially extract sensitive information from other origins, manipulate data across security boundaries, or execute unauthorized operations that should be restricted by standard browser security policies.
The operational impact of this vulnerability extends beyond simple data theft, as it fundamentally undermines the isolation guarantees that modern web browsers provide to users. Attackers can leverage this weakness to perform cross-site scripting attacks, extract cookies or session information from other domains, access local storage or database contents from different origins, and potentially escalate privileges within the browser environment. The medium severity classification reflects the fact that while the vulnerability requires a crafted HTML page to exploit, it provides significant capabilities for remote attackers who can deliver malicious content through various vectors including phishing campaigns, compromised websites, or social engineering attacks. This weakness particularly affects users who browse untrusted or compromised websites, as the attack surface expands to include interactions with other origins within the browser's security model.
Mitigation strategies for this vulnerability should focus on immediate patching of affected Chrome versions to ensure users are running the fixed version 151.0.7922.72 or later, which includes proper policy enforcement mechanisms that prevent the bypass of same origin restrictions. Organizations should implement comprehensive browser update management policies to ensure all systems receive security patches promptly and maintain awareness of the specific Chromium security advisory related to this issue. Additional defensive measures include implementing content security policies that restrict cross-origin resource sharing, enabling strict browser security settings, and monitoring for unusual network traffic patterns that might indicate exploitation attempts. From a broader security perspective, this vulnerability highlights the importance of proper policy enforcement in multi-process web environments and demonstrates how seemingly minor implementation flaws can create significant security risks when they affect core browser security mechanisms.
The technical nature of this vulnerability aligns with CWE-284 (Improper Access Control) and relates to ATT&CK techniques such as T1059 (Command and Scripting Interpreter) and T1566 (Phishing) where attackers leverage browser security weaknesses to establish persistent access or extract sensitive information. Security practitioners should consider this vulnerability in their risk assessments for web applications and browser-based environments, particularly when evaluating the security posture of systems that rely heavily on Chrome's multi-process architecture for isolation. The fix implemented by Google addresses the underlying policy enforcement mechanisms to ensure proper same origin policy enforcement while maintaining legitimate cross-origin communication capabilities that are essential for modern web applications to function correctly.