CVE-2026-84120

MEDIUM 5.4CVE-2026-84120 · Published 01/09/2026 · updated 02/09/2026

In short

CVE-2026-84120 is a MEDIUM (CVSS 5.4) vulnerability affecting firefox (mozilla), thunderbird (mozilla).
Chance of exploitation in the next 30 days (EPSS): 0.22%, higher than 12.4% of all vulnerabilities.
Fix: update to 140.15.0, 153.2.0, 155.0.0, 115.40.0 or later.

Package	Affected versions	Patched versions
firefox mozilla	`≥ 116.0, < 140.15.0≥ 141.0.0, < 153.2.0≥ 154.0.0, < 155.0.0< 115.40.0`	`140.15.0153.2.0155.0.0115.40.0`
thunderbird mozilla	`≥ 141.0, < 153.2.0≥ 154.0, < 155.0< 140.15.0`	`153.2.0155.0140.15.0`

Description

Use-after-free in the Audio/Video 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

bugzilla.mozilla.org/show_bug.cgi · Permissions Required
mozilla.org/security/advisories/mfsa2026-82 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-83 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-84 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-85 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-86 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-87 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-88 · Vendor Advisory

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Package

Affected versions

Patched versions

firefox

mozilla

≥ 116.0, < 140.15.0≥ 141.0.0, < 153.2.0≥ 154.0.0, < 155.0.0< 115.40.0

140.15.0153.2.0155.0.0115.40.0

thunderbird

mozilla

≥ 141.0, < 153.2.0≥ 154.0, < 155.0< 140.15.0

153.2.0155.0140.15.0

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