CVE-2026-84121 Affecting firefox-esr package, versions <140.15.0esr-1~deb13u1
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-DEBIAN13-FIREFOXESR-19477616
- published2 Sept 2026
- disclosed1 Sept 2026
Introduced: 1 Sep 2026
NewCVE-2026-84121 (opens in a new tab)How to fix?
Upgrade Debian:13 firefox-esr to version 140.15.0esr-1~deb13u1 or higher.
NVD Description
Note: Versions mentioned in the description apply only to the upstream firefox-esr package and not the firefox-esr package as distributed by Debian.
See How to fix? for Debian:13 relevant fixed versions and status.
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, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
References
- https://security-tracker.debian.org/tracker/CVE-2026-84121
- https://bugzilla.mozilla.org/show_bug.cgi?id=2059018
- https://www.mozilla.org/security/advisories/mfsa2026-82/
- https://www.mozilla.org/security/advisories/mfsa2026-83/
- https://www.mozilla.org/security/advisories/mfsa2026-84/
- https://www.mozilla.org/security/advisories/mfsa2026-85/
- https://www.mozilla.org/security/advisories/mfsa2026-86/
- https://www.mozilla.org/security/advisories/mfsa2026-87/
- https://www.mozilla.org/security/advisories/mfsa2026-88/