CVE-2026-100771

HIGH 8.1CVE-2026-100771 · Published 29/09/2026 · updated 06/10/2026

In short

CVE-2026-100771 is a HIGH (CVSS 8.1) vulnerability affecting firefox (mozilla), thunderbird (mozilla).
Chance of exploitation in the next 30 days (EPSS): 0.31%, higher than 23.7% of all vulnerabilities.
Fix: update to 115.42.0, 140.17.0, 153.4.0, 157.0.0 or later.

Package	Affected versions	Patched versions
firefox mozilla	`≥ 115.0, < 115.42.0≥ 140.0.0, < 140.17.0≥ 153.0, < 153.4.0≥ 154.0.0, < 157.0.0`	`115.42.0140.17.0153.4.0157.0.0`
thunderbird mozilla	`≥ 140.0, < 140.17.0≥ 153.0, < 153.4.0≥ 154.0, < 157.0`	`140.17.0153.4.0157.0`

Description

Undefined behavior in the DOM: Streams 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

≥ 115.0, < 115.42.0≥ 140.0.0, < 140.17.0≥ 153.0, < 153.4.0≥ 154.0.0, < 157.0.0

115.42.0140.17.0153.4.0157.0.0

thunderbird

mozilla

≥ 140.0, < 140.17.0≥ 153.0, < 153.4.0≥ 154.0, < 157.0

140.17.0153.4.0157.0

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