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Critical· 9.8official fix available

CVE-2026-16358

CVE-2026-16358 is a critical site isolation vulnerability in Firefox's WebRender graphics component, allowing potential attacks to bypass security boundaries. It was fixed in Firefox 153, Firefox ESR 115.38/140.13, and Thunderbird 153/140.13.

publishedJul 21, 2026
last modifiedJul 24, 2026
sourcesNVD
severity · cvss
9.8
critical · how bad it is
exploitation · epss
<1%
12th 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

Users of Firefox (versions <153), Firefox ESR (versions <115.38 or <140.13), and Thunderbird (versions <153 or <140.13)

02

Real-world impact

Attackers could exploit this to compromise user data or system integrity by breaking isolation between trusted and untrusted web content.

03

Why this severity

CVSS 9.8 (critical): High risk due to network accessibility, low attack complexity, and full impact on confidentiality, integrity, and availability.

04

What to do about it

official fix available
recommended steps
  1. 01Upgrade Firefox to version 153 or later.
  2. 02Update Firefox ESR to version 115.38 or 140.13.
  3. 03Upgrade Thunderbird to version 153 or 140.13.

NVD-referenced vendor advisory (fixed versions listed in NVD description)

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 impactHigh
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-2026-16358: CVE-2026-16358 is a critical site isolation vulnerability in Firefox's · Vulnary