Critical· 9.8official fix available
CVE-2026-16407
A critical vulnerability (CVSS 9.8) in the DOM Service Workers component allows a mitigation bypass. It affects Firefox and Thunderbird and was resolved in version 153 of both products. No known exploitation or public exploit is reported.
publishedJul 21, 2026
last modifiedJul 24, 2026
sourcesNVD
severity · cvss
9.8
critical · how bad it is
exploitation · epss
<1%
20th 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 21, 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
An attacker could bypass security mitigations, potentially leading to full compromise of confidentiality, integrity, and availability.
03
Why this severity
CVSS 9.8 reflects network‑adjacent, low‑complexity attack with no privileges or user interaction required, resulting in high impact across all three security properties.
04
What to do about it
official fix available
recommended steps
- 011. Upgrade Firefox to version 153 or later.
- 022. Upgrade Thunderbird to version 153 or later.
NVD-referenced vendor advisory
05
Timeline
- Jul 21, 2026 · 12d agoPublishedDisclosed and added to the National Vulnerability Database.
- Jul 22, 2026 · 10d agoOfficial fix availableA vendor patch or mitigation now exists — see the remediation steps above.
- Jul 24, 2026 · 9d agoAdvisory updatedThe 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
- bugzilla.mozilla.org/show_bug.cgipermissions required
- mozilla.org/security/advisories/mfsa202…vendor advisory
- mozilla.org/security/advisories/mfsa202…vendor advisory
(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 →