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Critical· 9.1official fix available

CVE-2026-16370

This vulnerability lets attackers bypass security checks in the browser or email client, allowing them to read or change data shown in web pages or emails. It was fixed 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 browsers (any version before 153).

02

Real-world impact

An attacker could read or modify sensitive information displayed in the browser or email client, potentially leading to data theft or manipulation.

03

Why this severity

The CVSS score of 9.1 reflects that the flaw can be exploited remotely without authentication, giving attackers full 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.
  3. 03Restart the application.

NVD-referenced vendor advisory

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 →
CVE-2026-16370: This vulnerability lets attackers bypass security checks in the browse · Vulnary