CVE-2026-78939: Google Chrome Use After Free Vulnerability

CVE-2026-78939 Overview

CVE-2026-78939 is a use-after-free vulnerability in the Chromecast component of Google Chrome versions prior to 152.0.7977.65. A remote attacker who has already compromised the renderer process can leverage the flaw to execute arbitrary code outside the browser sandbox. Exploitation requires user interaction, typically by luring a victim to a crafted HTML page. Google classifies the Chromium security severity as High. The issue is tracked under CWE-416: Use After Free.

Critical Impact
Successful exploitation results in sandbox escape and arbitrary code execution on the host, giving attackers a foothold outside the constrained renderer process.

Affected Products

Google Chrome (Desktop) versions prior to 152.0.7977.65
Chromium-based browsers embedding the vulnerable Chromecast component
Downstream distributions shipping affected Chrome builds

Discovery Timeline

2026-08-25 - CVE-2026-78939 published to NVD
2026-08-27 - Last updated in NVD database

Technical Details for CVE-2026-78939

Vulnerability Analysis

The flaw resides in Chrome's Chromecast integration, which handles device discovery and media casting from the browser. A use-after-free condition occurs when the component references heap memory that has already been released. An attacker who controls the renderer process can manipulate object lifetimes to reclaim the freed allocation with attacker-shaped data. Dereferencing the stale pointer transfers execution flow into memory the attacker controls. Because Chromecast logic runs in a more privileged context than the renderer sandbox, successful exploitation crosses the sandbox boundary.

This vulnerability chains with a prior renderer compromise, making it a second-stage primitive in a full exploit chain rather than a standalone entry point. It carries a CVSS scope change because the impact extends beyond the initially vulnerable component.

Root Cause

The root cause is improper object lifetime management in the Chromecast component [CWE-416]. Code paths retain raw pointers or references to Chromecast-related objects after their destructors run. When those pointers are later reused, the underlying memory may hold attacker-supplied content, enabling type confusion or virtual-function pointer hijacking.

Attack Vector

Attack delivery starts with a crafted HTML page that first exploits an independent renderer bug. Once the renderer is compromised, the attacker issues carefully sequenced inter-process messages or DOM operations that touch the Chromecast subsystem. The specific triggering sequence has not been publicly disclosed. Refer to the Chromium Issue Tracker #513261751 and the Google Chrome Desktop Update advisory for vendor-provided technical detail as it becomes available.

Detection Methods for CVE-2026-78939

Indicators of Compromise

Chrome renderer or utility process crashes referencing Chromecast, cast_channel, or media router modules on versions prior to 152.0.7977.65.
Unexpected child processes spawned by chrome.exe shortly after visiting an untrusted HTML page.
Outbound connections from Chrome-hosted processes to non-Google infrastructure following a browsing session.

Detection Strategies

Inventory Chrome installations and flag any endpoint running a version older than 152.0.7977.65.
Hunt for anomalous process trees where Chrome child processes launch shells, script hosts, or LOLBins.
Correlate browser crash telemetry with subsequent persistence or credential-access activity on the same host.

Monitoring Recommendations

Ingest Chrome update and version telemetry into your SIEM to track patch compliance across the fleet.
Monitor endpoint EDR events for memory-corruption signatures and sandbox-escape behaviors originating from the browser.
Alert on Chromecast-related DNS or mDNS traffic patterns paired with unusual local process activity.

How to Mitigate CVE-2026-78939

Immediate Actions Required

Update Google Chrome to version 152.0.7977.65 or later on all managed endpoints.
Force-restart Chrome after deployment to ensure the patched binary is loaded into memory.
Audit Chromium-based browsers and embedded frameworks for equivalent upstream fixes.

Patch Information

Google addressed the vulnerability in the Chrome Stable channel release documented in the Google Chrome Desktop Update advisory. Administrators should confirm rollout via enterprise management policies and verify installed versions through chrome://settings/help. Additional technical context is tracked in Chromium Issue Tracker #513261751.

Workarounds

Disable the Chromecast media router via enterprise policy EnableMediaRouter set to false where casting is not required.
Restrict outbound mDNS and Chromecast discovery traffic on untrusted network segments.
Enforce site isolation and block execution of untrusted HTML content through browser policy or web filtering.

bash

# Example enterprise policy to disable the media router (Chromecast)
# Windows registry path
HKLM\Software\Policies\Google\Chrome\EnableMediaRouter = 0 (DWORD)

# macOS configuration profile key
defaults write com.google.Chrome EnableMediaRouter -bool false

# Linux managed policy JSON
# /etc/opt/chrome/policies/managed/disable_cast.json
{
  "EnableMediaRouter": false
}