Critical· 9.8official fix available
CVE-2026-16401
A critical privilege‑escalation flaw (CVSS 9.8) exists in the Data Loss Prevention component. The vulnerability allows an attacker with no privileges to gain full control of the affected system. It was addressed in Firefox 153 and Thunderbird 153.
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 21, 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 and Thunderbird prior to version 153.
02
Real-world impact
An attacker could exploit this flaw to execute arbitrary code, read or modify data, and disrupt service on the vulnerable host.
03
Why this severity
The CVSS v3.1 score of 9.8 reflects a network‑reachable attack with low complexity, no required privileges or user interaction, and high impact to confidentiality, integrity, and availability.
04
What to do about it
official fix available
recommended steps
- 01Upgrade Firefox to version 153 or later.
- 02Upgrade Thunderbird to version 153 or later.
- 03After upgrading, restart the browser or email client to ensure the fix is active.
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 →