CVE-2026-84121: Vulnerability in Mozilla Firefox
Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, and Thunderbird 155.
CVE-2026-84121: Vulnerability in Mozilla Firefox
Description
Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, and Thunderbird 155.
CVSS v3.1
Score 9.6critical
Weaknesses
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mozilla
- Date Reserved
- 2026-09-01T07:25:11.012Z
- Cvss Version
- null
- State
- PUBLISHED
- Remediation Level
- null
- Vendor Advisory Urls
- [{"url":"https://www.mozilla.org/security/advisories/mfsa2026-82/","vendor":"Mozilla"},{"url":"https://www.mozilla.org/security/advisories/mfsa2026-83/","vendor":"Mozilla"},{"url":"https://www.mozilla.org/security/advisories/mfsa2026-84/","vendor":"Mozilla"},{"url":"https://www.mozilla.org/security/advisories/mfsa2026-85/","vendor":"Mozilla"}]
Threat ID: 6a96cab0acd9273b49b68542
Added to database: 09/01/2026, 12:53:04 UTC
Last updated: 09/02/2026, 01:20:57 UTC
Views: 44
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.