What is the CVSS score of CVE-2026-8958?

CVE-2026-8958 has a CVSS 3.1 base score of 8.6 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N. EPSS exploitation probability: 0.0%.

Which versions of Mozilla Firefox are affected by CVE-2026-8958?

Firefox versions prior to 151 contain a sandbox escape vulnerability that enables malicious websites to leak sensitive data from browser processes, directly exposing employee devices to data…. A patch is available.

How to fix or mitigate CVE-2026-8958?

Within 24 hours, identify all Firefox installations in your environment and document current versions. Within 7 days, deploy Firefox 151 or later (or Firefox ESR 140.11 or later for extended support branch users) through your patch management system, prioritizing systems handling sensitive data or administrative access. Within 30 days, verify deployment success via automated compliance scanning and establish monitoring for any failed patch installations or exploitation attempts.

Mozilla Firefox CVE-2026-8958

EUVD-2026-30907 HIGH

Exposure of Resource to Wrong Sphere (CWE-668)

2026-05-19 mozilla

GHSA-gm4c-ph85-6chj

Information Disclosure Mozilla

8.6

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

8.6 HIGH

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

vuln.today AI

7.4 HIGH

Delivered via remote web content so AV:N/AC:L/PR:N, but a sandbox escape realistically needs the victim to load the page (UI:R); S:C for crossing the sandbox boundary, C:H with no integrity or availability impact.

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

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

SUSE

HIGH

qualitative

Red Hat

6.1 MEDIUM

qualitative

Primary rating from NVD.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

High

Integrity

None

Availability

None

Lifecycle Timeline

Analysis Generated

Jul 23, 2026 - 17:43 vuln.today

CVE Published

May 19, 2026 - 12:29 nvd

UNKNOWN (no severity yet)

CVE Published

May 19, 2026 - 12:29 cve.org

HIGH 8.6

DescriptionCVE.org

Information disclosure, sandbox escape in the Security: Process Sandboxing component. This vulnerability was fixed in Firefox 151 and Firefox ESR 140.11.

AnalysisAI

Sandbox escape and information disclosure in Mozilla Firefox's Process Sandboxing component allows a malicious web page to leak data across the security boundary that isolates content processes from the rest of the browser and host. All Firefox versions prior to 151 and ESR versions prior to 140.11 are affected. The scope-changed CVSS 3.1 score of 8.6 reflects that a successful attack crosses the sandbox boundary, though there is no public exploit identified at time of analysis and EPSS exploitation probability is very low (0.04%).

Technical ContextAI

The flaw resides in Firefox's Security: Process Sandboxing subsystem, the OS-level isolation layer (using platform sandbox primitives such as seccomp-bpf on Linux and equivalent mechanisms elsewhere) that confines untrusted web content running in child/content processes so it cannot freely read host resources or memory belonging to more privileged parts of the browser. The CWE-668 classification (Exposure of Resource to Wrong Sphere) indicates the root cause is that a resource which should remain confined to the sandboxed content sphere becomes reachable across that boundary, enabling information disclosure and escape from the confined process. The single affected product per CPE is cpe:2.3:a:mozilla:firefox (all versions up to the fixed releases); the same engine ships in Firefox ESR and is redistributed by Linux vendors, which is why Red Hat and SUSE appear in the tags.

RemediationAI

Vendor-released patch: Firefox 151 and Firefox ESR 140.11 - upgrade to these or later builds as the primary and complete fix. On enterprise/LTS channels, move ESR deployments to 140.11. For Linux distributions, apply the packaged updates such as SUSE-SU-2026:2039 (https://www.suse.com/support/update/SUSE-SU-2026:2039/) and the equivalent Red Hat erratum rather than the upstream tarball. Consult Mozilla advisories MFSA2026-46/-48/-50/-51 (e.g. https://www.mozilla.org/security/advisories/mfsa2026-50/) for the authoritative fixed-version mapping. Because this is a sandboxing defect with no configuration toggle, there is no reliable in-product workaround; if immediate patching is impossible, the compensating controls are to restrict browsing to trusted sites via web filtering/proxy allowlisting and to enforce automatic browser updates through enterprise policy - accepting that URL filtering only reduces, not eliminates, exposure to malicious or compromised pages.

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Vendor StatusVendor

SUSE

Severity: High

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-2026-8958 vulnerability details – vuln.today

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Mozilla Firefox CVE-2026-8958

Severity by source

CVSS VectorNVD

Lifecycle Timeline

DescriptionCVE.org

AnalysisAI

Technical ContextAI

RemediationAI

More in Mozilla

Same weakness CWE-668 – Exposure of Resource to Wrong Sphere

Same technique Information Disclosure

Vendor StatusVendor

SUSE

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External POC / Exploit Code