CVE-2026-87589 in Chrome
Summary
by MITRE • 09/09/2026
Incorrect authorization in SiteIsolation in Google Chrome prior to 153.0.8010.36 allowed a remote attacker who had compromised the renderer process to bypass system access restrictions 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 an incorrect authorization flaw within Google Chrome's Site Isolation mechanism represents a significant breach in the browser's multi-process architecture designed to isolate sensitive data between different origins. Prior to version 153.0.8010.36, this security feature failed to enforce strict access controls when handling cross-origin requests under specific conditions involving renderer process compromise. The core technical flaw lies in the failure of the Site Isolation policy to properly validate authorization contexts during inter-process communication or resource loading operations that span isolated browsing instances. This deficiency allows a malicious actor who has already achieved code execution within a compromised renderer process, typically through a separate vulnerability such as a sandbox escape or arbitrary JavaScript execution via a crafted HTML page, to bypass these isolation boundaries and access resources belonging to other sites or sensitive system components that should remain inaccessible due to the same-origin policy.
From an operational perspective, this flaw undermines one of Chrome's primary defense-in-depth strategies against cross-site scripting attacks and data exfiltration. Site Isolation is critical for preventing attackers from reading private information like cookies, local storage contents, or DOM elements from other sites even if they can execute scripts in a victim's browser. By allowing a compromised renderer to bypass these restrictions, the vulnerability effectively neutralizes this protection layer, enabling potential session hijacking, credential theft, or unauthorized access to sensitive web application data that was previously considered safe due to process isolation. The severity is classified as medium because while it requires an initial foothold in the renderer process, which itself is a significant barrier for many attackers, once achieved, the lateral movement capabilities are substantially enhanced compared to standard same-origin policy violations.
This vulnerability aligns with CWE-269, Improper Privilege Assignment, specifically regarding the failure of the browser engine to correctly assign and enforce access rights based on the origin context during internal operations. It also maps closely to MITRE ATT&CK techniques related to Defense Evasion, particularly those involving process injection or manipulation of security features to bypass monitoring and isolation controls. The exploitation vector is remote via a crafted HTML page, which implies that an attacker could host malicious content designed to trigger this authorization failure when visited by a user running the affected Chrome version.
Mitigation strategies primarily involve updating Google Chrome to version 153.0.8010.36 or later where these access control checks have been hardened and validated against cross-origin renderer interactions. For organizations unable to patch immediately, deploying browser security policies that restrict script execution from untrusted origins can provide a partial compensating control by reducing the likelihood of initial renderer compromise. Additionally, enabling strict Content Security Policy headers on web applications reduces the attack surface for any subsequent exploitation attempts that might rely on injecting malicious scripts into otherwise secure contexts. Continuous monitoring for anomalous cross-origin resource requests and ensuring that browser extensions do not inadvertently weaken Site Isolation settings are also recommended practices to maintain robust isolation boundaries against sophisticated multi-stage attacks.