CVE-2026-16377: Mitigation bypass in the PDF Viewer component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

criticalCVSS 9.8CVE-2026-16377

Mitigation bypass in the PDF Viewer component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: critical — CVSS 9.8
Published: 2026-07-21
Last updated: 2026-07-24
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-16377

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-163770.39% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 31% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-16377	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

high[NEW] [high] Mozilla Firefox and Firefox ESR: Multiple vulnerabilitiescert-bund
unknownMultiple vulnerabilities in Mozilla Thunderbird (July 23, 2026)cert-fr-avis
unknownMozilla Products Multiple Vulnerabilitieshkcert
unknownMultiple vulnerabilities in Mozilla products (July 22, 2026)cert-fr-avis
unknownDSA-6394-1 firefox-esr - security updatedebian

Recent advisories for Mitigation bypass in

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

criticalCVE-2026-16407: Mitigation bypass in the DOM: Service Workers component. This vulnerability was fixed in Firef…nvd · 2026-07-21
criticalCVE-2026-16406: Mitigation bypass in the Networking component. This vulnerability was fixed in Firefox 153 and…nvd · 2026-07-21
criticalCVE-2026-16394: Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 153 …nvd · 2026-07-21
criticalCVE-2026-16390: Mitigation bypass in the Enterprise Policies component. This vulnerability was fixed in Firefo…nvd · 2026-07-21
criticalCVE-2026-16383: Mitigation bypass in the DOM: Networking component. This vulnerability was fixed in Firefox 15…nvd · 2026-07-21
criticalCVE-2026-16382: Mitigation bypass in the DOM: Service Workers component. This vulnerability was fixed in Firef…nvd · 2026-07-21