CVE-2021-29980 – This vulnerability involves uninitialized memor... (How to Fix)

Q: How do I fix CVE-2021-29980?

1. Open the application (Thunderbird or Firefox). 2. Go to Help > About. 3. Allow the application to check for and install updates. 4. Restart the application as prompted.

Q: What is the severity of CVE-2021-29980?

CVE-2021-29980 has a CVSS score of 8.8 (HIGH). This vulnerability involves uninitialized memory in a canvas object in Mozilla Thunderbird and Firefox, which could lead to incorrect memory deallocation, memory corruption, and potentially exploitable crashes. It affects Thunderbird versions before 78.13 and 91, Firefox ESR before 78.13, and Firefox before 91. Attackers could exploit this to execute arbitrary code or cause denial of service.

📋 TL;DR

This vulnerability involves uninitialized memory in a canvas object in Mozilla Thunderbird and Firefox, which could lead to incorrect memory deallocation, memory corruption, and potentially exploitable crashes. It affects Thunderbird versions before 78.13 and 91, Firefox ESR before 78.13, and Firefox before 91. Attackers could exploit this to execute arbitrary code or cause denial of service.

💻 Affected Systems

Products:

Mozilla Thunderbird
Mozilla Firefox
Mozilla Firefox ESR

Versions: Thunderbird < 78.13, Thunderbird < 91, Firefox ESR < 78.13, Firefox < 91

Operating Systems: All supported platforms (Windows, macOS, Linux)

Default Config Vulnerable: ⚠️ Yes

Notes: All default installations of affected versions are vulnerable; no special configuration required.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution leading to full system compromise, data theft, or malware installation.

🟠

Likely Case

Application crash (denial of service) or memory corruption leading to unstable behavior.

🟢

If Mitigated

Limited impact if patched or isolated; crashes may occur but exploitation is prevented.

🌐 Internet-Facing: HIGH - Web browsers and email clients are directly exposed to malicious content from the internet.

🏢 Internal Only: MEDIUM - Internal use still poses risk from malicious emails or web content, but attack surface is reduced.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires triggering the memory corruption via crafted web content or email; no public proof-of-concept is known.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Thunderbird 78.13 or 91, Firefox ESR 78.13, Firefox 91

Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2021-33/

Restart Required: Yes

Instructions:

1. Open the application (Thunderbird or Firefox). 2. Go to Help > About. 3. Allow the application to check for and install updates. 4. Restart the application as prompted.

🔧 Temporary Workarounds

Disable JavaScript

all

Disabling JavaScript can reduce the attack surface by preventing execution of malicious scripts that might trigger the vulnerability.

In Firefox/Thunderbird: about:config > Set javascript.enabled to false

🧯 If You Can't Patch

Restrict access to untrusted web content and email sources to minimize exposure.
Use application sandboxing or isolation techniques to limit potential impact if exploitation occurs.

🔍 How to Verify

Check if Vulnerable:

Check the application version in Help > About; if version is below the patched versions listed, it is vulnerable.

Check Version:

On Linux: thunderbird --version or firefox --version; On Windows/macOS: Use Help > About in the application.

Verify Fix Applied:

After updating, confirm the version is at least Thunderbird 78.13 or 91, Firefox ESR 78.13, or Firefox 91.

📡 Detection & Monitoring

Log Indicators:

Application crash logs with memory corruption errors
Unexpected termination of Thunderbird or Firefox processes

Network Indicators:

Unusual outbound connections from the application post-crash
Requests to known malicious domains

SIEM Query:

Example: event_source="application" AND (app_name="thunderbird" OR app_name="firefox") AND event_type="crash"

📊 Metadata

CVE ID: CVE-2021-29980

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-909

Published: August 17, 2021

Last Updated: November 21, 2024

🔗 References

https://bugzilla.mozilla.org/show_bug.cgi?id=1722204 Exploit,Issue Tracking,Vendor Advisory
https://security.gentoo.org/glsa/202202-03 Third Party Advisory
https://security.gentoo.org/glsa/202208-14 Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-33/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-34/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-35/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-36/ Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1722204 Exploit,Issue Tracking,Vendor Advisory
https://security.gentoo.org/glsa/202202-03 Third Party Advisory
https://security.gentoo.org/glsa/202208-14 Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-33/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-34/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-35/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-36/ Vendor Advisory

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