Vulnary
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Critical· 9.1official fix available

CVE-2026-16380

A critical mitigation bypass exists in the networking component of Firefox and Thunderbird, allowing attackers to bypass security controls. The flaw carries a CVSS score of 9.1. It was resolved in Firefox 153 and Thunderbird 153.

publishedJul 21, 2026
last modifiedJul 24, 2026
sourcesNVD
severity · cvss
9.1
critical · how bad it is
exploitation · epss
<1%
23th 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 22, 2026

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

01

Who is affected

Firefox and Thunderbird users

02

Real-world impact

Potential bypass of network‑level mitigations leading to further compromise.

03

Why this severity

CVSS 9.1 (Critical) due to network attack vector, low complexity, no privileges or user interaction required, high confidentiality and integrity impact.

04

What to do about it

official fix available
recommended steps
  1. 01Upgrade Firefox to version 153 or later.
  2. 02Upgrade Thunderbird 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 23, 2026 · 10d ago
    Official fix available
    A vendor patch or mitigation now exists — see the remediation steps above.
  3. Jul 24, 2026 · 9d ago
    Advisory updated
    The NVD record was last revised.
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 →