CVE-2020-6556 – CVE-2020-6556 is a heap buffer overflow vulnera... (How to Fix)

Q: What is the severity of CVE-2020-6556?

CVE-2020-6556 has a CVSS score of 8.8 (HIGH). CVE-2020-6556 is a heap buffer overflow vulnerability in SwiftShader, Chrome's software renderer, that allows remote attackers to potentially execute arbitrary code or cause heap corruption via a malicious HTML page. This affects all users of Google Chrome before version 84.0.4147.135. Attackers can exploit this by tricking users into visiting a specially crafted webpage.

📋 TL;DR

CVE-2020-6556 is a heap buffer overflow vulnerability in SwiftShader, Chrome's software renderer, that allows remote attackers to potentially execute arbitrary code or cause heap corruption via a malicious HTML page. This affects all users of Google Chrome before version 84.0.4147.135. Attackers can exploit this by tricking users into visiting a specially crafted webpage.

💻 Affected Systems

Products:

Google Chrome
Chromium-based browsers
Operating systems using Chrome components

Versions: All versions prior to 84.0.4147.135

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

Default Config Vulnerable: ⚠️ Yes

Notes: SwiftShader is used when hardware acceleration is unavailable or disabled, making this vulnerability relevant even on systems without GPU support.

📦 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...

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⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with the same privileges as the Chrome process, potentially leading to full system compromise, data theft, or malware installation.

🟠

Likely Case

Browser crash (denial of service) or limited memory corruption that could be leveraged for information disclosure or further exploitation.

🟢

If Mitigated

Minimal impact if Chrome sandboxing works correctly, potentially limiting exploitation to the browser process only.

🌐 Internet-Facing: HIGH - Attackers can host malicious websites accessible from the internet, requiring only a user to visit the page.

🏢 Internal Only: MEDIUM - Risk exists if internal users browse to compromised internal sites or external sites, but attack surface is more limited than internet-facing.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires bypassing Chrome's sandbox and other security mitigations, but heap buffer overflows in renderers are commonly exploited. The bug report (crbug.com/1115345) contains technical details that could aid exploitation.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 84.0.4147.135 and later

Vendor Advisory: https://chromereleases.googleblog.com/2020/08/stable-channel-update-for-desktop_18.html

Restart Required: Yes

Instructions:

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

🔧 Temporary Workarounds

Disable SwiftShader

all

Force Chrome to use hardware rendering only, which may prevent exploitation but could degrade performance on systems without GPU support.

chrome://flags/#disable-accelerated-2d-canvas
Set to 'Disabled'
Restart Chrome

Enable Site Isolation

all

Enhances Chrome's sandboxing to limit the impact of renderer compromises.

chrome://flags/#enable-site-per-process
Set to 'Enabled'
Restart Chrome

🧯 If You Can't Patch

Restrict web browsing to trusted sites only using browser policies or network filtering.
Deploy application control to block execution of unauthorized Chrome processes or child processes.

🔍 How to Verify

Check if Vulnerable:

Check Chrome version: If version is less than 84.0.4147.135, the system is vulnerable.

Check Version:

On Windows/Linux/macOS: google-chrome --version or navigate to chrome://version/

Verify Fix Applied:

Confirm Chrome version is 84.0.4147.135 or higher after update.

📡 Detection & Monitoring

Log Indicators:

Chrome crash reports with SwiftShader-related modules
Unexpected Chrome child process terminations
Security event logs showing Chrome accessing unusual memory regions

Network Indicators:

HTTP requests to known malicious domains hosting exploit code
Unusual outbound connections from Chrome processes post-crash

SIEM Query:

source="chrome_crash_reports" AND (process="chrome.exe" OR process="chrome") AND module="swiftshader"

📊 Metadata

CVE ID: CVE-2020-6556

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-787

Published: September 21, 2020

Last Updated: November 21, 2024

🔗 References

http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00049.html Mailing List,Third Party Advisory
https://chromereleases.googleblog.com/2020/08/stable-channel-update-for-desktop_18.html Vendor Advisory
https://crbug.com/1115345 Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EE7XWIZBME7JAY7N6CGPET4CLNHHEIVT/
https://www.debian.org/security/2021/dsa-4824 Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00049.html Mailing List,Third Party Advisory
https://chromereleases.googleblog.com/2020/08/stable-channel-update-for-desktop_18.html Vendor Advisory
https://crbug.com/1115345 Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EE7XWIZBME7JAY7N6CGPET4CLNHHEIVT/
https://www.debian.org/security/2021/dsa-4824 Third Party Advisory

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