CVE-2026-4711: Use-after-free in the Widget: Cocoa component

Q: How do I fix CVE-2026-4711?

firefox: upgrade to 140.9.0, 149.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-4711 being exploited?

CVE-2026-4711 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-4711 affect?

CVE-2026-4711 affects firefox. Severity is critical (CVSS 9.8). Use-after-free in the Widget: Cocoa component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Q: How urgent is CVE-2026-4711?

Priority 48/100. Critical severity; Remotely exploitable, no login, no user action

This month

CRITICAL 9.8REMOTEUPGRADE

CVE-2026-4711 is a critical-severity flaw (CVSS 9.8) affecting firefox. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Use-after-free in the Widget: Cocoa component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 65%)
CISA exploited list	No
Weakness	CWE-416
Published	2026-03-24
Last modified	2026-06-17

Publisher (CNA): Mozilla Corporation · Vendor: mozilla

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-24 13:16 UTCPublished CVE record published
2026-06-17 10:57 UTCUpdated Record last modified

mozilla firefox UPGRADE

Affected: < 140.9.0 · < 149.0

Fixed in: 140.9.0, 149.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy firefox || rpm -q firefox || firefox --version

2. UPGRADE to 140.9.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade firefox

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade firefox

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-4711?

firefox: upgrade to 140.9.0, 149.0. Exact commands for each OS are on this page.

Is CVE-2026-4711 being exploited?

CVE-2026-4711 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-4711 affect?

CVE-2026-4711 affects firefox. Severity is critical (CVSS 9.8). Use-after-free in the Widget: Cocoa component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

How urgent is CVE-2026-4711?

Priority 48/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

Mozilla Firefox vulnerabilities · Mozilla Thunderbird vulnerabilities

Related CVEs

CVE-2026-100801 HIGH 8.8 UPGRADE UPGRADE Privilege escalation in the DLL Services component
CVE-2026-6746 HIGH 7.5 UPGRADE UPGRADE Use-after-free in the DOM: Core & HTML component
CVE-2026-6758 HIGH 7.5 UPGRADE UPGRADE Use-after-free in the JavaScript: WebAssembly component
CVE-2026-6771 CRITICAL 9.8 UPGRADE UPGRADE Mitigation bypass in the DOM: Security component
CVE-2026-6747 HIGH 7.5 UPGRADE UPGRADE Use-after-free in the WebRTC component

References

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