CVE-2023-25739 – This vulnerability is a use-after-free flaw in ... (How to Fix)

Q: How do I fix CVE-2023-25739?

1. Open browser/mail client. 2. Go to Settings/Preferences > General/Advanced. 3. Click 'Check for updates'. 4. Install available updates. 5. Restart the application.

Q: What is the severity of CVE-2023-25739?

CVE-2023-25739 has a CVSS score of 8.8 (HIGH). This vulnerability is a use-after-free flaw in Firefox, Thunderbird, and Firefox ESR that occurs when failed module load requests aren't properly checked for cancellation. Attackers could exploit this to execute arbitrary code or cause crashes. All users of affected versions are at risk.

📋 TL;DR

This vulnerability is a use-after-free flaw in Firefox, Thunderbird, and Firefox ESR that occurs when failed module load requests aren't properly checked for cancellation. Attackers could exploit this to execute arbitrary code or cause crashes. All users of affected versions are at risk.

💻 Affected Systems

Products:

Mozilla Firefox
Mozilla Thunderbird
Mozilla Firefox ESR

Versions: Firefox < 110, Thunderbird < 102.8, Firefox ESR < 102.8

Operating Systems: Windows, Linux, macOS, Android

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations are vulnerable. JavaScript must be enabled (default).

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

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

🟠

Likely Case

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

🟢

If Mitigated

No impact if patched; sandboxing may limit damage if exploited.

🌐 Internet-Facing: HIGH - Web browsers are internet-facing by nature and can be exploited via malicious websites.

🏢 Internal Only: MEDIUM - Internal users could be targeted via phishing or compromised internal sites.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires JavaScript execution and bypassing browser security mitigations like ASLR.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Firefox 110, Thunderbird 102.8, Firefox ESR 102.8

Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2023-05/

Restart Required: Yes

Instructions:

1. Open browser/mail client. 2. Go to Settings/Preferences > General/Advanced. 3. Click 'Check for updates'. 4. Install available updates. 5. Restart the application.

🔧 Temporary Workarounds

Disable JavaScript

all

Prevents exploitation by blocking JavaScript execution, which is required for this vulnerability.

Use Content Security Policy

all

Implement CSP headers to restrict script sources and reduce attack surface.

🧯 If You Can't Patch

Restrict access to untrusted websites using web filtering or firewall rules.
Implement application whitelisting to prevent unauthorized browser execution.

🔍 How to Verify

Check if Vulnerable:

Check browser version: Firefox: Help > About Firefox; Thunderbird: Help > About Thunderbird.

Check Version:

firefox --version (Linux), or check via GUI on Windows/macOS.

Verify Fix Applied:

Verify version is Firefox ≥110, Thunderbird ≥102.8, or Firefox ESR ≥102.8.

📡 Detection & Monitoring

Log Indicators:

Browser crash logs with memory corruption signatures
Unexpected process termination

Network Indicators:

Requests to known malicious domains hosting exploit code
Unusual JavaScript loading patterns

SIEM Query:

source="browser_logs" AND (event="crash" OR event="memory_error") AND version<"110"

📊 Metadata

CVE ID: CVE-2023-25739

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-416

Published: June 2, 2023

Last Updated: January 9, 2025

🔗 References

https://bugzilla.mozilla.org/show_bug.cgi?id=1811939 Issue Tracking,Permissions Required
https://www.mozilla.org/security/advisories/mfsa2023-05/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2023-06/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2023-07/ Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1811939 Issue Tracking,Permissions Required
https://www.mozilla.org/security/advisories/mfsa2023-05/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2023-06/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2023-07/ Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1811939 Issue Tracking,Permissions Required

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