CVE-2026-87606 in Chrome
Summary
by MITRE • 09/09/2026
Missing authorization in SiteIsolation in Google Chrome prior to 153.0.8010.36 allowed a remote attacker who had compromised the renderer process to bypass site isolation via a crafted HTML page. (Chromium security severity: Medium)
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified as missing authorization within the SiteIsolation mechanism of Google Chrome prior to version 153.0.8010.36 represents a critical failure in browser-based process separation controls. Site Isolation is a fundamental security architecture designed to prevent cross-site attacks by ensuring that each site runs in its own unique renderer process, thereby isolating sensitive data and preventing malicious scripts from accessing information belonging to other origins. This specific flaw allows an attacker who has already achieved code execution within a compromised renderer process to bypass these isolation boundaries through the exploitation of crafted HTML content. The severity is classified as medium by Chromium security standards, reflecting its potential for significant privilege escalation relative to the initial compromise state but acknowledging that it requires prior foothold in the renderer environment rather than direct remote code execution from an untrusted origin without any preconditions.
From a technical perspective, this vulnerability stems from insufficient authorization checks during inter-process communication or context validation within the browser's rendering engine. When a malicious HTML page is rendered, it may attempt to access resources or perform actions that are restricted by the site isolation policy. Due to the missing authorization logic, the renderer process fails to properly validate whether the requesting entity has legitimate permission to interact with specific isolated contexts or data structures. This oversight enables the attacker to manipulate internal browser states or retrieve sensitive information from other sites that should remain strictly segregated. The exploitation vector relies on a crafted HTML page which leverages this gap in authorization verification, effectively tricking the browser into treating cross-origin requests as if they were within the same origin context, thus nullifying the protective barriers intended by Site Isolation.
The operational impact of this vulnerability is substantial for users relying on Chrome for secure web browsing and sensitive transactions. By bypassing site isolation, an attacker can potentially access cookies, local storage, or other persistent data associated with different websites that a user has visited. This capability facilitates sophisticated cross-site scripting attacks where malicious scripts from one domain can read or modify content in another, leading to account takeover, session hijacking, and unauthorized data exfiltration. Furthermore, the breach of isolation boundaries undermines trust in the browser's security model, as it allows lateral movement within the user's browsing context without requiring elevated privileges on the host operating system. This significantly expands the attack surface for web-based threats that previously relied on traditional cross-site scripting limitations to contain damage.
Mitigation strategies primarily involve immediate software updates to address the underlying code defects in the authorization checks. Users and administrators must upgrade Google Chrome to version 153.0.8010.36 or later, where these missing authorizations have been corrected and proper validation logic has been implemented within the Site Isolation framework. In environments where immediate patching is not feasible, network-level controls such as strict Content Security Policy headers can help mitigate some downstream effects by restricting script execution contexts, although they do not fix the root cause in the browser engine itself. Additionally, enabling enhanced security features like Safe Browsing and ensuring that third-party cookies are restricted can reduce the likelihood of initial renderer compromise through malicious ads or scripts.
This vulnerability aligns with CWE-269, which describes Improper Privilege Assignment, as it involves a failure to correctly enforce access controls within the application's internal processes. It also relates to CWE-863, concerning Incorrect Authorization, specifically in the context of checking permissions for actions that should be restricted by security policies like site isolation. From an offensive security perspective, this flaw supports ATT&CK technique T1059, Command and Scripting Interpreter, particularly when used in conjunction with browser-based exploitation techniques to maintain persistence or escalate privileges within the user's session after initial compromise via web delivery mechanisms. Understanding these mappings helps security teams prioritize remediation efforts based on standardized vulnerability classification frameworks.