CVE-2021-21203 – This is a use-after-free vulnerability in Googl... (How to Fix)

Q: What is the severity of CVE-2021-21203?

CVE-2021-21203 has a CVSS score of 8.8 (HIGH). This is a use-after-free vulnerability in Google Chrome's Blink rendering engine that allows remote attackers to potentially exploit heap corruption. Attackers can craft malicious HTML pages to trigger memory corruption, potentially leading to arbitrary code execution. All users running Chrome versions prior to 90.0.4430.72 are affected.

📋 TL;DR

This is a use-after-free vulnerability in Google Chrome's Blink rendering engine that allows remote attackers to potentially exploit heap corruption. Attackers can craft malicious HTML pages to trigger memory corruption, potentially leading to arbitrary code execution. All users running Chrome versions prior to 90.0.4430.72 are affected.

💻 Affected Systems

Products:

Google Chrome
Chromium-based browsers

Versions: All versions prior to 90.0.4430.72

Operating Systems: Windows, Linux, macOS, Android, Chrome OS

Default Config Vulnerable: ⚠️ Yes

Notes: All default Chrome configurations are vulnerable. Chromium-based browsers may also be affected depending on their Blink engine version.

📦 What is this software?

Chrome by Google

Google Chrome is the world's most popular web browser, used by over 3 billion users globally across Windows, macOS, Linux, Android, and iOS platforms. As a Chromium-based browser developed by Google, Chrome dominates the browser market with approximately 65% market share, making it a critical compon...

Learn more about Chrome →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with the same privileges as the Chrome process, potentially leading to full system compromise if Chrome is running with elevated privileges.

🟠

Likely Case

Browser crash (denial of service) or limited code execution within Chrome's sandbox, potentially allowing data theft or further exploitation.

🟢

If Mitigated

Browser crash with no data compromise if sandboxing works correctly and no additional vulnerabilities are chained.

🌐 Internet-Facing: HIGH - Attackers can exploit via malicious websites or ads without user interaction beyond visiting a page.

🏢 Internal Only: MEDIUM - Requires user to visit malicious internal web pages or click malicious links in emails.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Use-after-free vulnerabilities in browser engines are commonly exploited in the wild, but no specific weaponization evidence is publicly available for this CVE.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 90.0.4430.72 and later

Vendor Advisory: https://chromereleases.googleblog.com/2021/04/stable-channel-update-for-desktop_14.html

Restart Required: Yes

Instructions:

1. Open Chrome and click the three-dot menu. 2. Go to Help > About Google Chrome. 3. Chrome will automatically check for updates and install version 90.0.4430.72 or later. 4. Click 'Relaunch' to restart Chrome with the update.

🔧 Temporary Workarounds

Disable JavaScript

all

Temporarily disable JavaScript to prevent exploitation via malicious HTML pages

chrome://settings/content/javascript

Use Site Isolation

all

Ensure site isolation is enabled to limit impact of potential exploitation

chrome://flags/#enable-site-per-process (ensure enabled)

🧯 If You Can't Patch

Restrict browser usage to trusted websites only
Implement network filtering to block malicious HTML content

🔍 How to Verify

Check if Vulnerable:

Check Chrome version: If version is less than 90.0.4430.72, system is vulnerable.

Check Version:

google-chrome --version (Linux) or chrome://version (all platforms)

Verify Fix Applied:

Verify Chrome version is 90.0.4430.72 or higher after update.

📡 Detection & Monitoring

Log Indicators:

Chrome crash reports with memory corruption errors
Unexpected Chrome process termination

Network Indicators:

Requests to known malicious domains serving crafted HTML
Unusual outbound connections from Chrome processes

SIEM Query:

process_name:"chrome.exe" AND (event_id:1000 OR event_id:1001) AND description:"EXCEPTION_ACCESS_VIOLATION"

📊 Metadata

CVE ID: CVE-2021-21203

CVSS v3 Score: 8.8 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CWE: CWE-416

Published: April 26, 2021

Last Updated: November 21, 2024

🔗 References

https://chromereleases.googleblog.com/2021/04/stable-channel-update-for-desktop_14.html Release Notes,Vendor Advisory
https://crbug.com/1192054 Permissions Required,Vendor Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EAJ42L4JFPBJATCZ7MOZQTUDGV4OEHHG/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U3GZ42MYPGD35V652ZPVPYYS7A7LVXVY/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VUZBGKGVZADNA3I24NVG7HAYYUTOSN5A/
https://security.gentoo.org/glsa/202104-08 Third Party Advisory
https://www.debian.org/security/2021/dsa-4906 Third Party Advisory
https://chromereleases.googleblog.com/2021/04/stable-channel-update-for-desktop_14.html Release Notes,Vendor Advisory
https://crbug.com/1192054 Permissions Required,Vendor Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EAJ42L4JFPBJATCZ7MOZQTUDGV4OEHHG/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U3GZ42MYPGD35V652ZPVPYYS7A7LVXVY/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VUZBGKGVZADNA3I24NVG7HAYYUTOSN5A/
https://security.gentoo.org/glsa/202104-08 Third Party Advisory
https://www.debian.org/security/2021/dsa-4906 Third Party Advisory

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🔗 Related Vulnerabilities

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📋 TL;DR

💻 Affected Systems

📦 What is this software?

Chrome by Google

Debian Linux by Debian

Fedora by Fedoraproject

Fedora by Fedoraproject

Fedora by Fedoraproject

⚠️ Risk & Real-World Impact

Worst Case

Likely Case

If Mitigated

🎯 Exploit Status

🛠️ Fix & Mitigation

✅ Official Fix

Instructions:

🔧 Temporary Workarounds

Disable JavaScript

Use Site Isolation

🧯 If You Can't Patch

🔍 How to Verify

Check if Vulnerable:

Check Version:

Verify Fix Applied:

📡 Detection & Monitoring

Log Indicators:

Network Indicators:

SIEM Query:

📊 Metadata

🔗 References

📤 Share & Export

🔗 Related Vulnerabilities