CVE-2024-0743 – This vulnerability involves an unchecked return... (How to Fix)

Q: How do I fix CVE-2024-0743?

1. Open the affected application. 2. Go to Help > About Firefox/Thunderbird. 3. Allow the application to check for and install updates. 4. Restart the application when prompted.

Q: What is the severity of CVE-2024-0743?

CVE-2024-0743 has a CVSS score of 7.5 (HIGH). This vulnerability involves an unchecked return value in TLS handshake code in Mozilla products, which could cause a potentially exploitable crash. It affects users of Firefox versions before 122, Firefox ESR before 115.9, and Thunderbird before 115.9.

📋 TL;DR

This vulnerability involves an unchecked return value in TLS handshake code in Mozilla products, which could cause a potentially exploitable crash. It affects users of Firefox versions before 122, Firefox ESR before 115.9, and Thunderbird before 115.9.

💻 Affected Systems

Products:

Mozilla Firefox
Mozilla Firefox ESR
Mozilla Thunderbird

Versions: Firefox < 122, Firefox ESR < 115.9, Thunderbird < 115.9

Operating Systems: All platforms supported by affected Mozilla products

Default Config Vulnerable: ⚠️ Yes

Notes: All configurations using TLS/SSL connections are affected. No special configuration required to be vulnerable.

📦 What is this software?

Firefox by Mozilla

View all CVEs affecting Firefox →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution leading to complete system compromise if an attacker can trigger the crash in a controlled manner.

🟠

Likely Case

Denial of service through application crash during TLS handshake, potentially disrupting secure communications.

🟢

If Mitigated

Application instability or unexpected termination without further compromise if crash is not exploitable.

🌐 Internet-Facing: HIGH - Web browsers and email clients frequently process untrusted TLS connections from the internet.

🏢 Internal Only: MEDIUM - Internal TLS connections could still trigger the vulnerability, but attack surface is reduced.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires triggering the TLS handshake flaw, which could be done via malicious websites or email servers. No public exploit code has been disclosed.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Firefox 122, Firefox ESR 115.9, Thunderbird 115.9

Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2024-01/

Restart Required: Yes

Instructions:

1. Open the affected application. 2. Go to Help > About Firefox/Thunderbird. 3. Allow the application to check for and install updates. 4. Restart the application when prompted.

🔧 Temporary Workarounds

Disable TLS connections

all

Prevent the application from making TLS connections, which would avoid triggering the vulnerability but breaks secure web browsing/email.

🧯 If You Can't Patch

Restrict network access to only trusted websites and email servers
Use alternative browsers/email clients until patches can be applied

🔍 How to Verify

Check if Vulnerable:

Check application version in Help > About Firefox/Thunderbird and compare to affected versions.

Check Version:

firefox --version or thunderbird --version on command line

Verify Fix Applied:

Verify version is Firefox ≥122, Firefox ESR ≥115.9, or Thunderbird ≥115.9 after update.

📡 Detection & Monitoring

Log Indicators:

Application crash logs mentioning TLS handshake
Unexpected browser/email client termination

Network Indicators:

Failed TLS handshakes followed by application termination

SIEM Query:

source="*firefox*" OR source="*thunderbird*" AND (event="crash" OR event="terminated") AND message="*TLS*"

📊 Metadata

CVE ID: CVE-2024-0743

CVSS v3 Score: 7.5 (HIGH)

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

CWE: CWE-252

Published: January 23, 2024

Last Updated: November 3, 2025

🔗 References

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🔗 Related Vulnerabilities

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