# Multiple vulnerabilities in Mozilla Firefox and Thunderbird

Published: 2026-09-02 · Severity: elevated
Canonical: https://vorant.io/reports/e198fd6f-15cc-54df-b2db-eb8520e5cabb/multiple-vulnerabilities-in-mozilla-firefox-and-thunderbird

> Multiple vulnerabilities in Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR enable privilege escalation, data breach, and security policy bypass.

CERT-FR has published an advisory covering multiple vulnerabilities affecting Mozilla Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR products. The vulnerabilities span several impact categories including privilege escalation, confidentiality breaches, security policy bypass, and denial of service. Affected versions include Firefox versions prior to 155, Firefox ESR versions prior to 115.40, 140.15, and 153.2, as well as corresponding Thunderbird releases. The advisory references seven Mozilla security bulletins (mfsa2026-82 through mfsa2026-88) covering the identified issues. Defenders should prioritize patching affected systems to the latest available versions. The specific technical details and individual CVE impacts are documented in Mozilla's official security advisories, which should be consulted for comprehensive remediation guidance.

## Mentioned in this report

- Vulnerabilities: CVE-2026-16365, CVE-2026-16371, CVE-2026-74952, CVE-2026-75874, CVE-2026-84117, CVE-2026-84118, CVE-2026-84119, CVE-2026-84120, CVE-2026-84121, CVE-2026-84122, CVE-2026-84123, CVE-2026-84124, CVE-2026-84125, CVE-2026-84126, CVE-2026-84127, CVE-2026-84128, CVE-2026-84129, CVE-2026-84130, CVE-2026-84131, CVE-2026-84132, CVE-2026-84133, CVE-2026-84134, CVE-2026-84135, CVE-2026-84136, CVE-2026-84137, CVE-2026-84138, CVE-2026-84139, CVE-2026-84140, CVE-2026-84141, CVE-2026-84142, CVE-2026-84143, CVE-2026-84144, CVE-2026-84145, CVE-2026-84637, CVE-2026-84639, CVE-2026-84640, CVE-2026-84641, CVE-2026-84642

Source reporting: https://www.cert.ssi.gouv.fr/avis/CERTFR-2026-AVI-1106

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