CVE-2026-4691 | Use-after-free in the CSS Parsing and Computation component.… | CVSS 9.8 CRITICAL

Description

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

Metadata

CVE ID: CVE-2026-4691
State: PUBLISHED
Assigner: mozilla
Reserved: 2026-03-23 23:21 UTC
Published: 2026-03-24 12:30 UTC
Last updated: 2026-07-15 00:49 UTC
Primary CWE: CWE-416
CWE-416 Use After Free
Vendor / Product: Mozilla / Firefox
Sources: cve.org · NVD

Severity & Metrics

9.8 CRITICAL CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

SSVC — CISA Coordinator

Exploitation: none
Automatable: yes
Tech. Impact: total

Affected products (2)

Vendor	Product	Platform	Versions
Mozilla	Firefox	—	115.34 ≤ 115., 140.9 ≤ 140., 149 ≤ *
Mozilla	Thunderbird	—	140.9 ≤ 140., 149 ≤

Weakness (CWE)

CWE	Source	Description
CWE-416	adp	CWE-416 Use After Free
CWE-825	adp	Expired Pointer Dereference

CVSS scores (2)

Score	Severity	Version	Source	Vector
9.8	CRITICAL	3.1	adp	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5	HIGH	3.1	adp	CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

References (6)