CVE-2026-8401: Sandbox escape in the Profile Backup component

Q: How do I fix CVE-2026-8401?

firefox: upgrade to 150.0.3. Exact commands for each OS are on this page.

Q: Is CVE-2026-8401 being exploited?

CVE-2026-8401 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-2026-8401 affect?

CVE-2026-8401 affects firefox. Severity is critical (CVSS 9.8). Sandbox escape in the Profile Backup component. This vulnerability was fixed in Firefox 150.0.3, Firefox ESR 115.36, Firefox ESR 140.11, and Thunderbird 140.11.

Q: How urgent is CVE-2026-8401?

Priority 45/100. Critical severity; Remotely exploitable, no login, no user action

This month

CRITICAL 9.8REMOTEUPGRADE

CVE-2026-8401 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.

Sandbox escape in the Profile Backup component. This vulnerability was fixed in Firefox 150.0.3, Firefox ESR 115.36, Firefox ESR 140.11, and Thunderbird 140.11.

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	0.3% (top 76%)
CISA exploited list	No
Weakness	CWE-693, CWE-653
Published	2026-05-12
Last modified	2026-10-26

Publisher (CNA): Mozilla Corporation · Vendor: mozilla

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-12 15:16 UTCPublished CVE record published
2026-10-26 18:10 UTCUpdated Record last modified

mozilla firefox UPGRADE

Affected: < 150.0.3

Fixed in: 150.0.3

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 150.0.3 (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.

Advisories and coverage

Official advisories

AlmaLinux Errata: [ALSA-2026:21381] Important: thunderbird security update 2026-05-29
AlmaLinux Errata: [ALSA-2026:21378] Important: firefox security update 2026-05-29

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-2026-8401?

firefox: upgrade to 150.0.3. Exact commands for each OS are on this page.

Is CVE-2026-8401 being exploited?

CVE-2026-8401 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-2026-8401 affect?

CVE-2026-8401 affects firefox. Severity is critical (CVSS 9.8). Sandbox escape in the Profile Backup component. This vulnerability was fixed in Firefox 150.0.3, Firefox ESR 115.36, Firefox ESR 140.11, and Thunderbird 140.11.

How urgent is CVE-2026-8401?

Priority 45/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

Mozilla Firefox vulnerabilities · Mozilla Thunderbird vulnerabilities

Related CVEs

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CVE-2026-8092 HIGH 8.1 UPGRADE UPGRADE Memory safety bugs present in Thunderbird ESR 140.10.1 and Thunderbird 150.0.1
CVE-2026-6750 HIGH 8.8 UPGRADE UPGRADE Privilege escalation in the Graphics: WebRender component
CVE-2026-5733 HIGH 8.8 UPGRADE Incorrect boundary conditions in the Graphics: WebGPU component

References

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