What’s Vulnerable › Vulnerabilities

CVE-2026-4691: Use-after-free in the CSS Parsing and Computation component

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-24 · updated 2026-07-15
• Weakness: CWE-416

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.

Affected products

• Mozilla Firefox: before 115.34.0; before 149.0; from 128.0 before 140.9.0 — fixed in 115.34.0, 140.9.0, 149.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.34.0, 140.9.0, 149.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2017512
• https://www.mozilla.org/security/advisories/mfsa2026-20/
• https://www.mozilla.org/security/advisories/mfsa2026-21/
• https://www.mozilla.org/security/advisories/mfsa2026-22/
• https://www.mozilla.org/security/advisories/mfsa2026-23/
• https://www.mozilla.org/security/advisories/mfsa2026-24/
• https://access.redhat.com/errata/RHSA-2026:5930
• https://access.redhat.com/errata/RHSA-2026:5931
• https://access.redhat.com/errata/RHSA-2026:5932
• https://access.redhat.com/errata/RHSA-2026:6188
• https://access.redhat.com/errata/RHSA-2026:6342
• https://access.redhat.com/errata/RHSA-2026:6917

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