Use-After-Free Vulnerability in Firefox Browser by Mozilla
CVE-2026-0884

9.8CRITICAL

Key Information:

Vendor

Mozilla
Status
Firefox
Firefox Esr
Thunderbird
Vendor
CVE Published:
13 January 2026

What is CVE-2026-0884?

A use-after-free vulnerability has been identified in the JavaScript Engine component of the Firefox browser. This flaw can potentially allow an attacker to exploit the memory management functionality of the browser, leading to unexpected behavior or system compromise. Users of Firefox versions prior to 147 and Firefox ESR versions below 140.7 are recommended to update their browsers to mitigate such risks. Mozilla encourages all users to ensure they are using the most recent versions to maintain optimum security levels.

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Deploy the Patch

Affected Version(s)

Firefox < 147

Firefox ESR < 140.7

Thunderbird < 147

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2003588
https://www.mozilla.org/security/advisories/mfsa2026-01/
https://www.mozilla.org/security/advisories/mfsa2026-03/

CVSS V3.1

Score:
9.8
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Gary Kwong and Nan Wang
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