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CVE-2026-4691

CRITICAL CVSS 3.1: 9.8
Updated Mar 24, 2026
Mozilla
Parameter Value
CVSS 9.8 (CRITICAL)
Affected Versions 128.0 — 149.0
Fixed In 115.34.0
Type CWE-416 (Use After Free)
Vendor Mozilla
Public PoC No

Use-after-free in the CSS Parsing and Computation component. This vulnerability affects Firefox < 149, Firefox ESR < 115.34, and Firefox ESR < 140.9.

Attack Parameters

Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed

Impact Assessment

Confidentiality
High
Complete data leak
Integrity
High
Complete data modification
Availability
High
Complete denial of service

CVSS Vector v3.1

Weakness Type (CWE)

Vulnerable Products 3

Configuration From (including) Up to (excluding)
Mozilla Firefox
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
115.34.0
Mozilla Firefox
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
149.0
Mozilla Firefox
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
128.0 140.9.0