CVE-2021-38493 – This CVE describes memory safety bugs in Mozill... (How to Fix)

Q: How do I fix CVE-2021-38493?

1. Open affected browser. 2. Go to Settings > Help > About Firefox/Thunderbird. 3. Allow automatic update to latest version. 4. Restart browser when prompted.

Q: What is the severity of CVE-2021-38493?

CVE-2021-38493 has a CVSS score of 8.8 (HIGH). This CVE describes memory safety bugs in Mozilla Firefox and Thunderbird that could lead to memory corruption. With sufficient effort, attackers could exploit these vulnerabilities to execute arbitrary code on affected systems. Users running Firefox ESR versions below 78.14, Thunderbird below 78.14, or Firefox below 92 are vulnerable.

📋 TL;DR

This CVE describes memory safety bugs in Mozilla Firefox and Thunderbird that could lead to memory corruption. With sufficient effort, attackers could exploit these vulnerabilities to execute arbitrary code on affected systems. Users running Firefox ESR versions below 78.14, Thunderbird below 78.14, or Firefox below 92 are vulnerable.

💻 Affected Systems

Products:

Firefox ESR
Thunderbird
Firefox

Versions: Firefox ESR < 78.14, Thunderbird < 78.14, Firefox < 92

Operating Systems: All platforms supported by affected browsers

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations of affected versions are vulnerable. No special configuration required for exploitation.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution leading to complete system compromise, data theft, or ransomware deployment.

🟠

Likely Case

Browser crashes or instability, with potential for limited code execution in sandboxed environments.

🟢

If Mitigated

Minimal impact if browsers are fully patched and running with security controls like sandboxing enabled.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: HIGH

Exploitation requires significant effort due to memory corruption bugs, but could be achieved through malicious web content without user authentication.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Firefox ESR 78.14+, Thunderbird 78.14+, Firefox 92+

Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2021-38/

Restart Required: Yes

Instructions:

1. Open affected browser. 2. Go to Settings > Help > About Firefox/Thunderbird. 3. Allow automatic update to latest version. 4. Restart browser when prompted.

🔧 Temporary Workarounds

Disable JavaScript

all

Temporarily reduces attack surface by disabling JavaScript execution in browser.

about:config > javascript.enabled = false

🧯 If You Can't Patch

Restrict browser usage to trusted websites only
Implement network segmentation to isolate vulnerable browsers from critical systems

🔍 How to Verify

Check if Vulnerable:

Check browser version in About dialog: Firefox ESR must be 78.14+, Thunderbird 78.14+, or Firefox 92+.

Check Version:

firefox --version | thunderbird --version

Verify Fix Applied:

Confirm version number matches patched versions after update and restart.

📡 Detection & Monitoring

Log Indicators:

Browser crash reports with memory access violations
Unexpected browser process termination

Network Indicators:

Unusual outbound connections from browser processes
Traffic to known malicious domains

SIEM Query:

source="browser_logs" AND (event="crash" OR event="memory_error") AND version<"92"

📊 Metadata

CVE ID: CVE-2021-38493

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: November 3, 2021

Last Updated: November 21, 2024

🔗 References

https://bugzilla.mozilla.org/buglist.cgi?bug_id=1723391%2C1724101%2C1724107 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/mfsa2021-38/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-39/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-42/ Vendor Advisory
https://bugzilla.mozilla.org/buglist.cgi?bug_id=1723391%2C1724101%2C1724107 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/mfsa2021-38/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-39/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-42/ Vendor Advisory

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🔗 Related Vulnerabilities

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