What is the CVSS score of CVE-2026-8401?

CVE-2026-8401 has a CVSS 3.1 base score of 9.8 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.0%.

Which versions of Mozilla Firefox are affected by CVE-2026-8401?

Mozilla Firefox prior to version 150.0.3 contains a critical sandbox escape vulnerability enabling remote attackers to break the browser's security isolation and access the host operating system…. A patch is available.

How to fix or mitigate CVE-2026-8401?

Within 24 hours, alert security staff and IT teams of the critical vulnerability and begin immediate inventory of Firefox versions across all systems. Within 7 days, deploy Mozilla Firefox version 150.0.3 or later to all affected systems using your standard patch management procedures, prioritizing user workstations and development machines. Within 30 days, verify patching completion through automated endpoint scanning and confirm that zero instances of Firefox prior to 150.0.3 remain active in your environment.

Mozilla Firefox CVE-2026-8401

EUVD-2026-29493 CRITICAL

Protection Mechanism Failure (CWE-693)

2026-05-12 mozilla

GHSA-rr5w-74h2-xqhc

Information Disclosure Mozilla

9.8

CVSS 3.1 · Vendor: mozilla

Severity by source

Vendor (mozilla) PRIMARY

9.8 CRITICAL

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

vuln.today AI

8.3 HIGH

Sandbox escape realistically requires a chained content compromise and user navigation (UI:R, AC:H), but escaping isolation is a scope change (S:C) yielding full host-context impact.

3.1 AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H

4.0 AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

SUSE

CRITICAL

qualitative

Red Hat

7.5 HIGH

qualitative

Primary rating from Vendor (mozilla).

CVSS VectorVendor: mozilla

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Generated

Jul 23, 2026 - 22:28 vuln.today

CVSS changed

May 14, 2026 - 20:22 NVD

9.8 (CRITICAL)

CVE Published

May 12, 2026 - 14:24 nvd

CRITICAL 9.8

CVE Published

May 12, 2026 - 14:24 nvd

UNKNOWN (no severity yet)

DescriptionCVE.org

Sandbox escape in the Profile Backup component. This vulnerability was fixed in Firefox 150.0.3.

AnalysisAI

Sandbox escape in Mozilla Firefox's Profile Backup component allows an attacker to break out of the browser's content-process isolation and gain broader access to the host, affecting versions prior to 150.0.3. There is no public exploit identified at time of analysis and EPSS estimates only a 0.02% exploitation probability, but SSVC rates the technical impact as total and the flaw automatable, so it warrants prompt patching. Not listed in CISA KEV.

Technical ContextAI

Firefox uses a multi-process, sandboxed architecture in which web content runs in low-privilege content processes that are isolated from the operating system and from privileged browser components. The Profile Backup component handles the user's profile data (bookmarks, settings, saved state), and a weakness here lets code cross the sandbox boundary that is supposed to contain a compromised content process. The assigned CWE-693 (Protection Mechanism Failure) reflects the root cause: an existing security control - the sandbox - fails to enforce isolation rather than a classic memory-corruption primitive. The only CPE provided is cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* with no version bound encoded, so the fixed-version boundary (150.0.3) comes from the Mozilla advisory text rather than the CPE range.

RemediationAI

Vendor-released patch: Firefox 150.0.3 - upgrade all Firefox installations to 150.0.3 or later per Mozilla advisory MFSA2026-45 (https://www.mozilla.org/security/advisories/mfsa2026-45/). On Linux, apply the corresponding distribution updates: SUSE via SUSE-SU-2026:2039 (https://www.suse.com/support/update/SUSE-SU-2026:2039/) and Red Hat via the RHSA-2026 errata (e.g. https://access.redhat.com/errata/RHSA-2026:21378). Because the flaw is in the browser's own sandbox rather than a toggleable feature, there is no clean product-side workaround; interim compensating controls are limited to reducing exposure to untrusted web content - enforce managed auto-update so users cannot run stale builds, and where feasible restrict browsing of untrusted sites or run Firefox under an additional OS-level sandbox/container (trade-off: added isolation may break some native integrations and does not address a determined chained exploit). Prioritize patching over these stopgaps.

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Vendor StatusVendor

SUSE

Severity: Critical

Product	Status
SUSE Linux Enterprise Server 12 SP5-LTSS	Fixed
SUSE Linux Enterprise Server LTSS Extended Security 12 SP5	Fixed
openSUSE Tumbleweed	Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS	Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS	Affected

CVE-2026-8401 vulnerability details – vuln.today

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Mozilla Firefox CVE-2026-8401

Severity by source

CVSS VectorVendor: mozilla

Lifecycle Timeline

DescriptionCVE.org

AnalysisAI

Technical ContextAI

RemediationAI

More in Mozilla

Same weakness CWE-693 – Protection Mechanism Failure

Same technique Information Disclosure

Vendor StatusVendor

SUSE

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External POC / Exploit Code