CVE-2026-87505 in Chrome
Summary
by MITRE • 09/09/2026
Incorrect authorization in FileSystem 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 PDF file. (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 the FileSystem component of Google Chrome prior to version 153.0.8010.36 represents a significant breach in the browser's multi-process architecture, specifically targeting the integrity of site isolation mechanisms. Site isolation is a critical security feature designed to prevent cross-site scripting attacks and data theft by ensuring that each website runs in its own unique process with restricted access to memory belonging to other sites. This vulnerability exploits a logic error where the FileSystem API fails to properly validate authorization checks when handling file operations initiated from renderer processes, thereby allowing a compromised renderer to escalate privileges beyond its intended sandbox boundaries.
From a technical perspective, the flaw stems from an insufficient verification of permissions during file system interactions within the Chromium engine. When a malicious PDF file is processed by Chrome's built-in viewer or associated plugins, it can trigger specific code paths that interact with local storage mechanisms without adequate checks against the origin policy. An attacker who has successfully compromised a renderer process through another vector, such as a remote code execution exploit in JavaScript or a plugin vulnerability, can leverage this authorization bypass to read sensitive files from the user's file system or write malicious data into restricted directories. This effectively neutralizes the sandboxing protections that are meant to contain damage within the isolated renderer environment, allowing lateral movement and access to resources that should remain inaccessible to web content.
The operational impact of this vulnerability is severe due to its potential for privilege escalation from a low-privilege context to one with broader system access. By bypassing site isolation, an attacker can potentially exfiltrate sensitive user data stored locally by the browser, such as cookies, session tokens, or cached credentials, which are typically protected against cross-origin requests. Furthermore, if the FileSystem API allows for write operations in certain configurations, the attacker could plant persistent malware or modify configuration files to maintain access after the victim closes the browser tab. This undermines the fundamental trust model of web browsers and exposes users to sophisticated attacks that combine remote exploitation with local system compromise.
This issue aligns closely with CWE-269, which describes Improper Privilege Assignment, as it involves a process operating at an elevated level of access without proper authorization checks. Additionally, from the perspective of the MITRE ATT&CK framework, this vulnerability facilitates techniques related to Defense Evasion and Credential Access, specifically allowing attackers to bypass application sandboxing mechanisms like T1608 or steal credentials via local file system access akin to T1530. The use of a crafted PDF file as the delivery mechanism highlights the risk associated with complex document parsers that often contain deep code paths susceptible to such logic errors when handling untrusted input.
Mitigation for this vulnerability requires immediate updating to Google Chrome version 153.0.8010.36 or later, where these authorization checks have been corrected and reinforced within the FileSystem implementation. Organizations should enforce automated update policies to ensure all endpoints are running patched versions of the browser. For environments where automatic updates cannot be immediately deployed, network-level controls such as web proxies can be configured to block access to known malicious domains hosting crafted PDF files or to restrict the execution of untrusted content that interacts with local file systems. Security teams should also monitor for unusual process behavior originating from renderer processes attempting to access sensitive directories outside their sandboxed scope, which may indicate an active exploitation attempt leveraging this flaw.