CVE-2026-87433: Google Chrome Race Condition Vulnerability

CVE-2026-87433 Overview

CVE-2026-87433 is a race condition vulnerability in the FileAPI component of Google Chrome versions prior to 153.0.8010.36. A remote attacker who has already compromised the renderer process can bypass site isolation by delivering a crafted HTML page. Site isolation is a core Chrome security boundary that separates content from different origins into distinct processes. Bypassing it allows an attacker to access cross-origin data that should remain protected. The issue is tracked as CWE-367: Time-of-Check Time-of-Use (TOCTOU) Race Condition and Chromium rates the underlying security severity as Medium.

Critical Impact
Successful exploitation enables cross-origin data access and site isolation bypass, undermining Chrome's fundamental process-based sandbox boundary.

Affected Products

Google Chrome (Desktop) versions prior to 153.0.8010.36
Chromium-based browsers that embed vulnerable FileAPI code
All supported desktop platforms (Windows, macOS, Linux) running affected Chrome builds

Discovery Timeline

2026-09-09 - CVE-2026-87433 published to the National Vulnerability Database (NVD)
2026-09-10 - Last updated in NVD database
Vendor advisory - Published in the Chrome Desktop Stable Channel Update

Technical Details for CVE-2026-87433

Vulnerability Analysis

The flaw is a race condition in Chrome's FileAPI implementation, the browser subsystem that exposes File, Blob, and related interfaces to web pages. FileAPI operations cross the renderer-to-browser boundary and involve asynchronous handoffs between processes. When two operations execute in an interleaved order that developers did not anticipate, a check performed before the operation can become stale by the time the operation actually runs. Attackers can exploit this window to reference file or blob resources associated with a different origin than the one currently being validated. The result is a site isolation bypass, meaning content protected by Chrome's process-per-site model can be reached from an attacker-controlled context.

Root Cause

The root cause is a Time-of-Check Time-of-Use (TOCTOU) condition classified under CWE-367. Origin or process ownership is validated at one point in the FileAPI request path, but the resource is consumed later without re-validating that the caller still owns it. A compromised renderer can race that validation to acquire references to blobs belonging to another site.

Attack Vector

Exploitation requires an already-compromised renderer process, typically achieved by chaining this issue with a prior renderer bug delivered through a crafted HTML page. Once the renderer is compromised, the attacker triggers the FileAPI race to escape site isolation and access cross-origin content. No verified proof-of-concept code is published; refer to the Chromium Issue Tracker entry #497574154 for technical details as they become available.

Detection Methods for CVE-2026-87433

Indicators of Compromise

Chrome browser processes on endpoints running versions earlier than 153.0.8010.36
Renderer processes exhibiting unexpected cross-origin resource access patterns
Browser crashes or renderer restarts correlated with visits to untrusted HTML content

Detection Strategies

Inventory installed Chrome versions across managed endpoints and flag builds below 153.0.8010.36
Monitor process telemetry for anomalous child-process spawning from chrome.exe renderers
Correlate web proxy or DNS logs with visits to unfamiliar domains preceding renderer instability

Monitoring Recommendations

Ingest endpoint browser telemetry into a centralized data lake for version and behavior analytics
Alert on Chrome installations that fall behind the vendor stable channel by more than one release
Track outbound connections from renderer processes for unusual cross-origin request patterns

How to Mitigate CVE-2026-87433

Immediate Actions Required

Update Google Chrome to version 153.0.8010.36 or later on all Windows, macOS, and Linux endpoints
Restart Chrome after the update so the patched binaries are loaded into active sessions
Verify Chromium-based third-party browsers ship a build that incorporates the upstream fix

Patch Information

Google addressed CVE-2026-87433 in the Chrome Stable Channel update to 153.0.8010.36. Full release notes and affected component information are published in the Chrome Desktop Stable Channel Update. Enterprises managing Chrome through Group Policy or MDM should push the updated version and confirm rollout via chrome://version on representative endpoints.

Workarounds

Restrict browsing to trusted sites until the patch is deployed to reduce initial renderer compromise risk
Enforce Chrome auto-update policies so future stable channel releases apply without user action
Use enterprise browser management to block extensions or content sources with elevated risk of hosting exploit chains

bash

# Verify installed Chrome version on Linux/macOS endpoints
google-chrome --version

# Windows: query the installed version via registry
reg query "HKLM\SOFTWARE\Google\Chrome\BLBeacon" /v version