High severity · published Jul 21, 2026
CVE-2026-16396
Privilege escalation in WebExtensions
8.8
CVSS
0.5%
EPSS
No
On KEV
Description
Privilege escalation in WebExtensions. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 39% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FI
Firefox · Mozilla
before 140.13.0; before 153.0.0 · source: NVD
TH
Thunderbird · Mozilla
before 140.13.0; 141.0 before 153.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-16396
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-16396
Permissions Required
https://bugzilla.mozilla.org/show_bug.cgi?id=2047240
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-68/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-70/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-71/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-72/
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