CVE-2025-6556: Google Chrome Auth Bypass Vulnerability

CVE-2025-6556 Overview

CVE-2025-6556 is a Content Security Policy (CSP) bypass vulnerability in the Loader component of Google Chrome versions prior to 138.0.7204.49. The flaw stems from insufficient policy enforcement [CWE-288], allowing a remote attacker to circumvent CSP restrictions through a crafted HTML page. Google rates the Chromium security severity as Low, while NVD assigns a CVSS 3.1 score of 5.4 (Medium). Successful exploitation requires user interaction, such as visiting an attacker-controlled web page. The vulnerability impacts confidentiality and integrity but does not affect availability.

Critical Impact
Attackers can bypass Content Security Policy in Chrome, weakening a primary browser defense against cross-site scripting and data exfiltration on visited pages.

Affected Products

Google Chrome versions prior to 138.0.7204.49
Chromium-based browsers sharing the affected Loader component
Desktop platforms covered by the Chrome Stable channel update

Discovery Timeline

2025-06-24 - CVE-2025-6556 published to NVD following the Chrome Stable channel update
2025-07-02 - Last updated in NVD database

Technical Details for CVE-2025-6556

Vulnerability Analysis

The vulnerability resides in the Chrome Loader, the component responsible for fetching and committing navigation and subresource requests. Insufficient policy enforcement means the Loader fails to consistently apply Content Security Policy directives during specific load operations. A remote attacker can craft an HTML page that triggers a load path where CSP checks are not enforced as intended.

The issue is classified under [CWE-288], which describes authentication or policy bypass through an alternate path or channel. In this case, the alternate path exists within the resource loading pipeline rather than at the policy decision point. The attacker leverages this gap to load or execute content that the page author intended CSP to block.

Exploitation requires user interaction, typically visiting a malicious page or one containing attacker-controlled markup. The impact is scoped to the browser process and the loaded origin, with no privilege escalation or sandbox escape.

Root Cause

The root cause is a gap between the Loader's request handling logic and the CSP enforcement layer. Certain load operations bypass the policy check that should reject disallowed sources. See the Chromium Issue Tracker Entry for additional technical context.

Attack Vector

The attack vector is network-based through a crafted HTML page. An attacker hosts malicious content on a controlled domain or injects markup into a vulnerable page. When a user loads the page, the Loader processes the crafted content without enforcing the expected CSP directives. The attacker can then execute scripts or load resources that CSP was configured to prevent.

No verified public proof-of-concept code is available. The vulnerability mechanism is described in prose based on the Chromium advisory and issue tracker.

Detection Methods for CVE-2025-6556

Indicators of Compromise

Browser telemetry showing script execution or resource loads that violate documented CSP headers on trusted internal applications
Web server logs recording unexpected outbound requests to attacker-controlled domains from pages with restrictive CSP policies
User reports of unexpected content rendering on internal web applications protected by CSP

Detection Strategies

Inventory Chrome installations across managed endpoints and flag any version prior to 138.0.7204.49
Monitor CSP violation reports collected through report-to or report-uri endpoints for anomalous patterns suggesting bypass attempts
Correlate browser process activity with outbound network connections to identify resource loads that should have been blocked by CSP

Monitoring Recommendations

Centralize CSP violation reports in a SIEM or data lake to baseline normal violation rates and detect spikes
Track Chrome version distribution through endpoint management tooling to verify patch deployment progress
Alert on access to known phishing or exploit-staging domains from outdated Chrome clients

How to Mitigate CVE-2025-6556

Immediate Actions Required

Update Google Chrome to version 138.0.7204.49 or later on all managed endpoints
Restart browsers after the update to ensure the patched Loader code is loaded
Verify Chromium-based browsers in the environment, such as Edge and Brave, have applied the equivalent upstream fix

Patch Information

Google released the fix in the Chrome Stable channel update on June 24, 2025. Details are available in the Google Chrome Update Announcement. Administrators should deploy version 138.0.7204.49 or later through enterprise update channels.

Workarounds

Enforce automatic Chrome updates through enterprise policy to minimize the window of exposure
Restrict browsing to trusted sites through web filtering until patches are confirmed deployed
Apply defense-in-depth controls such as DNS filtering and network egress restrictions to reduce the impact of CSP bypass on outbound data flows

bash

# Verify installed Chrome version on Windows endpoints
reg query "HKLM\Software\Google\Update\Clients\{8A69D345-D564-463C-AFF1-A69D9E530F96}" /v pv

# Verify installed Chrome version on macOS endpoints
defaults read /Applications/Google\ Chrome.app/Contents/Info CFBundleShortVersionString

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