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Critical· 9.1official fix available

CVE-2026-16394

A critical vulnerability (CVSS 9.1) in Firefox's DOM security component allows a mitigation bypass. The issue was resolved in Firefox 153 and Thunderbird 153. There is no known exploitation in the wild according to CISA KEV.

publishedJul 21, 2026
last modifiedJul 22, 2026
sourcesNVD
severity · cvss
9.1
critical · how bad it is
exploitation · epss
<1%
17th percentile · chance of exploitation in 30 days
(ai-assisted) A model wrote this summary from the official data, so double-check it against the source before you act on it. Read the official advisory →
auto-deletes from the system
counting…on Aug 20, 2026

An official fix is available, so this entry is kept for 30 days and then removed automatically.

01

Who is affected

Mozilla Firefox (and Thunderbird)

02

Real-world impact

An attacker could bypass security mitigations, potentially leading to further exploitation.

03

Why this severity

CVSS 9.1 reflects a network‑adjacent attack with low complexity, no privileges or user interaction required, and high impact on confidentiality and integrity.

04

What to do about it

official fix available
recommended steps
  1. 011. Upgrade Mozilla Firefox to version 153 or later.
  2. 022. If you use Thunderbird, upgrade it to version 153 or later.

NVD description indicating the fix in Firefox 153 and Thunderbird 153.

05

Timeline

  1. Jul 21, 2026 · 12d ago
    Published
    Disclosed and added to the National Vulnerability Database.
  2. Jul 21, 2026 · 11d ago
    Official fix available
    A vendor patch or mitigation now exists — see the remediation steps above.
06

How it’s attacked

Attack vectorNetwork (remote)
Attack complexityLow
Privileges requiredNone
User interactionNone needed
ScopeUnchanged
Confidentiality impactHigh
Integrity impactHigh
Availability impactNone
07

References & advisories

NVD advisory ↗Search advisories ↗
(ai-assisted) A model wrote this summary from the official data, so double-check it against the source before you act on it. Read the official advisory →