CVE-2026-78940 Overview
CVE-2026-78940 is an improper initialization vulnerability [CWE-665] in the Network component of Google Chrome. Versions prior to 152.0.7977.65 allow a remote attacker to bypass web origin policy through a crafted HTML page. Google's Chromium security team rated the severity as Medium.
The flaw undermines the same-origin policy, a foundational browser security boundary that isolates content between web origins. Exploitation requires only that a victim navigate to an attacker-controlled page.
Critical Impact
A remote attacker can bypass the web origin policy in Chrome via a crafted HTML page, potentially exposing cross-origin data or enabling unauthorized cross-origin actions.
Affected Products
- Google Chrome desktop versions prior to 152.0.7977.65
- Chromium-based builds incorporating the vulnerable Network component
- Downstream browsers derived from affected Chromium releases
Discovery Timeline
- 2026-08-25 - CVE-2026-78940 published to NVD
- 2026-08-26 - Last updated in NVD database
Technical Details for CVE-2026-78940
Vulnerability Analysis
The vulnerability resides in Chrome's Network stack. An improper initialization condition [CWE-665] leaves security-relevant state in an inconsistent form before it is consumed by origin-checking logic. When a crafted HTML page triggers the affected code path, the browser fails to enforce the web origin policy correctly.
The same-origin policy governs how documents and scripts from one origin can interact with resources from another. When origin enforcement is skipped or evaluated against uninitialized state, an attacker-controlled page can read or influence data associated with a different origin. Google classifies the Chromium severity as Medium, indicating exploitation typically yields limited cross-origin disclosure or manipulation rather than direct code execution.
Google addressed the issue in the Chrome Stable channel update announced on the Chrome Releases blog. The corresponding tracker entry is available on the Chromium Issue Tracker.
Root Cause
The root cause is improper initialization within the Network component. Data structures or flags used during request handling are not fully initialized before origin enforcement decisions are made, allowing origin policy checks to be bypassed under specific conditions.
Attack Vector
Exploitation is remote and requires user interaction. A victim visits a page hosting attacker-controlled HTML and JavaScript that constructs network requests or DOM interactions targeting the vulnerable initialization path. No authentication is required. Verified proof-of-concept code is not publicly available at this time.
Refer to the vendor references for technical specifics: the Chrome Stable Channel Update and the Chromium Issue Tracker Note.
Detection Methods for CVE-2026-78940
Indicators of Compromise
- Chrome or Chromium-based browser instances reporting version numbers below 152.0.7977.65 in endpoint inventory data.
- Web proxy or DNS logs showing user navigation to newly registered or low-reputation domains serving unusual HTML with cross-origin fetch or iframe patterns.
- Browser telemetry indicating unexpected cross-origin resource reads following visits to untrusted pages.
Detection Strategies
- Query endpoint management data to enumerate installed Chrome versions and flag hosts running builds prior to 152.0.7977.65.
- Alert on outbound HTTP requests to suspicious domains immediately followed by anomalous cross-origin traffic patterns from the browser process.
- Correlate browser process activity with sensitive-application session cookies being accessed shortly after visits to unclassified sites.
Monitoring Recommendations
- Ingest browser and proxy logs into a centralized data lake to enable version and behavior correlation across the fleet.
- Track Chrome Stable channel release notes and map new CVEs to detection rules and patch compliance dashboards.
- Monitor for exploitation research or public proof-of-concept publication referencing Chromium bug 511819962.
How to Mitigate CVE-2026-78940
Immediate Actions Required
- Update Google Chrome to version 152.0.7977.65 or later on all managed endpoints across Windows, macOS, and Linux.
- Restart Chrome after applying the update to ensure the patched binaries load; users often leave browsers running for extended periods.
- Identify Chromium-based browsers in the environment and confirm each vendor has released a corresponding patched build.
Patch Information
Google released the fix in Chrome Stable 152.0.7977.65. Deployment details are published in the Chrome Stable Channel Update. Enterprises using Chrome Browser Enterprise policies should validate that automatic updates are enabled or push the update via existing software distribution tooling.
Workarounds
- No vendor-supplied workaround exists; upgrading to the patched build is the only supported remediation.
- Restrict browsing to trusted sites through URL filtering or DNS policy on unpatched hosts until updates complete.
- Enforce Chrome auto-update policies via group policy or MDM to prevent version drift going forward.
# Verify installed Chrome version on Windows via registry
reg query "HKLM\SOFTWARE\Google\Update\Clients\{8A69D345-D564-463C-AFF1-A69D9E530F96}" /v pv
# Verify installed Chrome version on macOS
defaults read /Applications/Google\ Chrome.app/Contents/Info CFBundleShortVersionString
# Verify installed Chrome version on Linux
google-chrome --version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
