CVE-2020-26952 – This vulnerability in Firefox's JavaScript JIT ... (How to Fix)

Q: How do I fix CVE-2020-26952?

1. Open Firefox 2. Click menu → Help → About Firefox 3. Allow automatic update to Firefox 83 or later 4. Restart Firefox when prompted

Q: What is the severity of CVE-2020-26952?

CVE-2020-26952 has a CVSS score of 8.8 (HIGH). This vulnerability in Firefox's JavaScript JIT compiler could allow memory corruption when handling out-of-memory conditions. An attacker could potentially exploit this to execute arbitrary code or cause a denial of service. All Firefox users with versions below 83 are affected.

📋 TL;DR

This vulnerability in Firefox's JavaScript JIT compiler could allow memory corruption when handling out-of-memory conditions. An attacker could potentially exploit this to execute arbitrary code or cause a denial of service. All Firefox users with versions below 83 are affected.

💻 Affected Systems

Products:

Mozilla Firefox

Versions: All versions < 83

Operating Systems: Windows, Linux, macOS, Android

Default Config Vulnerable: ⚠️ Yes

Notes: All standard Firefox installations are vulnerable. No special configuration required.

📦 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, data theft, or malware installation.

🟠

Likely Case

Browser crash (denial of service) or limited memory corruption that could be leveraged for further exploitation.

🟢

If Mitigated

No impact if patched or if exploit attempts fail due to memory layout or other mitigations.

🌐 Internet-Facing: HIGH - Attackers can exploit via malicious websites or web content.

🏢 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: HIGH

Exploitation requires precise memory manipulation and may be unreliable across different systems.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Firefox 83 and later

Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2020-50/

Restart Required: Yes

Instructions:

1. Open Firefox
2. Click menu → Help → About Firefox
3. Allow automatic update to Firefox 83 or later
4. Restart Firefox when prompted

🔧 Temporary Workarounds

Disable JavaScript

all

Prevents JIT compilation by disabling JavaScript execution

about:config → javascript.enabled = false

Disable JIT compilation

all

Disables the vulnerable JIT compiler component

about:config → javascript.options.baselinejit = false
about:config → javascript.options.ion = false

🧯 If You Can't Patch

Restrict browser usage to trusted websites only
Implement application whitelisting to prevent unauthorized Firefox execution

🔍 How to Verify

Check if Vulnerable:

Check Firefox version in About Firefox dialog

Check Version:

firefox --version

Verify Fix Applied:

Confirm version is 83.0 or higher in About Firefox

📡 Detection & Monitoring

Log Indicators:

Firefox crash reports
Out of memory errors in browser logs
Unexpected process termination

Network Indicators:

Multiple connections to suspicious domains from Firefox
Unusual JavaScript execution patterns

SIEM Query:

source="firefox.log" AND ("crash" OR "segfault" OR "out of memory")

📊 Metadata

CVE ID: CVE-2020-26952

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: December 9, 2020

Last Updated: November 21, 2024

🔗 References

https://bugzilla.mozilla.org/show_bug.cgi?id=1667685 Issue Tracking,Permissions Required,Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-50/ Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1667685 Issue Tracking,Permissions Required,Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-50/ Vendor Advisory

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🔗 Related Vulnerabilities

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