CVE-2020-26971 – This vulnerability allows attackers to trigger ... (How to Fix)

Q: How do I fix CVE-2020-26971?

1. Open the application. 2. Go to Help > About Firefox/Thunderbird. 3. Allow automatic update or download from mozilla.org. 4. Restart the application.

Q: What is the severity of CVE-2020-26971?

CVE-2020-26971 has a CVSS score of 8.8 (HIGH). This vulnerability allows attackers to trigger a heap buffer overflow by providing specially crafted blit values to video drivers. Successful exploitation could lead to arbitrary code execution or application crashes. It affects Firefox, Thunderbird, and Firefox ESR users running vulnerable versions.

📋 TL;DR

This vulnerability allows attackers to trigger a heap buffer overflow by providing specially crafted blit values to video drivers. Successful exploitation could lead to arbitrary code execution or application crashes. It affects Firefox, Thunderbird, and Firefox ESR users running vulnerable versions.

💻 Affected Systems

Products:

Mozilla Firefox
Mozilla Thunderbird
Mozilla Firefox ESR

Versions: Firefox < 84, Thunderbird < 78.6, Firefox ESR < 78.6

Operating Systems: Windows, Linux, macOS

Default Config Vulnerable: ⚠️ Yes

Notes: Requires specific video drivers; not all systems may be exploitable.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with the privileges of the affected application, potentially leading to full system compromise if combined with privilege escalation.

🟠

Likely Case

Application crash (denial of service) or limited code execution within the browser sandbox.

🟢

If Mitigated

No impact if patched versions are deployed or if exploit attempts are blocked by security controls.

🌐 Internet-Facing: HIGH - Web browsers process untrusted content from the internet, making them prime targets.

🏢 Internal Only: MEDIUM - Internal users could be targeted via malicious internal websites or documents.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires bypassing browser security mechanisms like ASLR and sandboxing.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Firefox 84, Thunderbird 78.6, Firefox ESR 78.6

Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2020-54/

Restart Required: Yes

Instructions:

1. Open the application. 2. Go to Help > About Firefox/Thunderbird. 3. Allow automatic update or download from mozilla.org. 4. Restart the application.

🔧 Temporary Workarounds

Disable vulnerable video drivers

all

Update or disable video drivers that trigger the vulnerability.

🧯 If You Can't Patch

Disable JavaScript in the browser (reduces attack surface but impacts functionality).
Use application whitelisting to block execution of vulnerable versions.

🔍 How to Verify

Check if Vulnerable:

Check application version in Help > About Firefox/Thunderbird.

Check Version:

firefox --version (Linux) or check About dialog (Windows/macOS)

Verify Fix Applied:

Confirm version is Firefox ≥84, Thunderbird ≥78.6, or Firefox ESR ≥78.6.

📡 Detection & Monitoring

Log Indicators:

Application crash logs with memory corruption signatures.
Unexpected process termination in system logs.

Network Indicators:

Unusual web requests to malicious sites delivering exploit code.

SIEM Query:

source="application_logs" AND (event="crash" OR event="buffer_overflow") AND app_name IN ("firefox", "thunderbird")

📊 Metadata

CVE ID: CVE-2020-26971

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: January 7, 2021

Last Updated: November 21, 2024

🔗 References

https://bugzilla.mozilla.org/show_bug.cgi?id=1663466 Permissions Required,Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-54/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-55/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-56/ Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1663466 Permissions Required,Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-54/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-55/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-56/ Vendor Advisory

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🔗 Related Vulnerabilities

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