CVE-2026-100791

HIGH 8.8CVE-2026-100791 · Published 29/09/2026 · updated 19/10/2026

In short

CVE-2026-100791 is a HIGH (CVSS 8.8) vulnerability affecting firefox (mozilla), thunderbird (mozilla).
Chance of exploitation in the next 30 days (EPSS): 0.40%, higher than 33.8% of all vulnerabilities.
Fix: update to 140.17.0, 153.4.0, 157.0.0, 115.42.0 or later.

Package	Affected versions	Patched versions
firefox mozilla	`≥ 116.0, < 140.17.0≥ 141.0, < 153.4.0≥ 154.0.0, < 157.0.0< 115.42.0`	`140.17.0153.4.0157.0.0115.42.0`
thunderbird mozilla	`≥ 141.0, < 153.4.0≥ 154.0, < 157.0< 140.17.0`	`153.4.0157.0140.17.0`

Description

Use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.

References

bugzilla.mozilla.org/show_bug.cgi · Permissions Required
mozilla.org/security/advisories/mfsa2026-100 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-101 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-102 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-103 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-97 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-98 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-99 · Vendor Advisory

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Package

Affected versions

Patched versions

firefox

mozilla

≥ 116.0, < 140.17.0≥ 141.0, < 153.4.0≥ 154.0.0, < 157.0.0< 115.42.0

140.17.0153.4.0157.0.0115.42.0

thunderbird

mozilla

≥ 141.0, < 153.4.0≥ 154.0, < 157.0< 140.17.0

153.4.0157.0140.17.0

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