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CVE-2023-6863

8.8 HIGH

📋 TL;DR

This vulnerability in Firefox, Firefox ESR, and Thunderbird involves undefined behavior in the ShutdownObserver() function due to missing virtual destructor in a dynamic type. Attackers could potentially exploit this to execute arbitrary code or cause application crashes. All users of affected versions are at risk.

💻 Affected Systems

Products:
  • Firefox
  • Firefox ESR
  • Thunderbird
Versions: Firefox ESR < 115.6, Thunderbird < 115.6, Firefox < 121
Operating Systems: Windows, Linux, macOS, All supported platforms
Default Config Vulnerable: ⚠️ Yes
Notes: All standard installations are vulnerable; no special configuration required for exploitation.

📦 What is this software?

Debian Linux by Debian

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Debian Linux by Debian

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Debian Linux by Debian

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Firefox by Mozilla

View all CVEs affecting Firefox →

Firefox Esr by Mozilla

View all CVEs affecting Firefox Esr →

Thunderbird by Mozilla

View all CVEs affecting Thunderbird →

⚠️ Risk & Real-World Impact

🔴

Worst Case

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

🟠

Likely Case

Application crash (denial of service) or memory corruption leading to potential information disclosure.

🟢

If Mitigated

Limited impact with proper sandboxing and exploit mitigations; potential crash but no code execution.

🌐 Internet-Facing: HIGH - Web browsers are directly exposed to malicious content from the internet.
🏢 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 triggering the undefined behavior through crafted content; no public exploit code available.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Firefox ESR 115.6, Thunderbird 115.6, Firefox 121

Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2023-54/

Restart Required: Yes

Instructions:

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

🔧 Temporary Workarounds

Disable JavaScript

all

Reduces attack surface by preventing JavaScript execution which could trigger the vulnerability.

about:config → javascript.enabled = false

🧯 If You Can't Patch

  • Restrict browser usage to trusted websites only
  • Implement application whitelisting to prevent execution of vulnerable versions

🔍 How to Verify

Check if Vulnerable:

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

Check Version:

firefox --version or thunderbird --version

Verify Fix Applied:

Verify version is Firefox ESR ≥115.6, Thunderbird ≥115.6, or Firefox ≥121.

📡 Detection & Monitoring

Log Indicators:

  • Application crash logs
  • Unexpected termination events
  • Memory access violation errors

Network Indicators:

  • Unusual outbound connections after browser crash

SIEM Query:

source="firefox.log" OR source="thunderbird.log" AND (event="crash" OR event="segfault")

📊 Metadata

CVE ID: CVE-2023-6863
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
Published: December 19, 2023
Last Updated: November 21, 2024

🔗 References

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