What is the CVSS score of CVE-2026-8950?

CVE-2026-8950 has a contested CVSS base score of 9.3 from a third party (e.g. CISA-ADP), while the vendor rates it Critical. vuln.today uses the vendor rating as authoritative.

Which versions of Mozilla Firefox are affected by CVE-2026-8950?

Mozilla Firefox versions prior to 151 (and Firefox ESR before 140.11) contain a critical same-origin policy bypass vulnerability that allows malicious websites to access confidential data from other…. A patch is available.

How to fix or mitigate CVE-2026-8950?

Within 24 hours: Identify all Firefox deployments in your environment and verify patch compatibility with organizational systems. Within 7 days: Distribute and enforce updates to Firefox version 151 or later for standard users, and Firefox ESR version 140.11 or later for enterprise deployments; monitor rollout completion. Within 30 days: Verify all Firefox instances have been patched, conduct spot checks against confirmed versions, and document the patching timeline for audit purposes.

Mozilla Firefox CVE-2026-8950

EUVD-2026-30898 CRITICAL

Origin Validation Error (CWE-346)

2026-05-19 mozilla

GHSA-m49g-cq5x-4jmc

Authentication Bypass Mozilla

Critical

Disputed · 9.3 NVD

Severity by source

Sources disagree (Medium–Critical)

NVD PRIMARY

9.3 CRITICAL

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

vuln.today AI

8.2 HIGH

Network-reachable via a visited page (AV:N/AC:L/PR:N) but requires user interaction (UI:R); cross-origin read crosses a trust boundary (S:C) yielding high confidentiality, limited integrity, no availability impact.

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

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

SUSE

CRITICAL

qualitative

Red Hat

6.1 MEDIUM

qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Analysis Generated

Jul 23, 2026 - 17:45 vuln.today

CVE Published

May 19, 2026 - 12:29 nvd

UNKNOWN (no severity yet)

CVE Published

May 19, 2026 - 12:29 cve.org

CRITICAL 9.3

DescriptionCVE.org

Same-origin policy bypass in the Networking: HTTP component. This vulnerability was fixed in Firefox 151 and Firefox ESR 140.11.

AnalysisAI

Same-origin policy bypass in Mozilla Firefox's Networking: HTTP component allows a malicious web page to read or interact with data belonging to another origin once a victim is lured into visiting it, defeating the browser's core cross-origin isolation boundary. It affects Firefox before 151 and Firefox ESR before 140.11 and carries a CVSS 9.3 rating driven by a scope change and high confidentiality impact, though there is no public exploit identified at time of analysis and EPSS exploitation probability is only 0.02% (4th percentile). Reported internally by Mozilla and shipped with a vendor patch, this is a browser-side flaw requiring user interaction rather than a server-side or unauthenticated-automation risk.

Technical ContextAI

The vulnerability lives in Firefox's HTTP networking stack, which is responsible for enforcing the same-origin policy (SOP) - the fundamental browser guarantee that content loaded from origin A cannot read responses or state belonging to origin B. The root cause is classified as CWE-346 (Origin Validation Error), meaning the browser failed to correctly validate or attribute the origin of an HTTP resource, letting one origin observe or reach across into another's protected data. Because Firefox and its Gecko engine underpin the browser as well as downstream builds packaged by Red Hat and SUSE (per the tags and the SUSE-SU-2026:2039 advisory), the same defect propagates into enterprise Linux distributions that ship Mozilla packages. The affected CPE is cpe:2.3:a:mozilla:firefox:*, and the parallel ESR fix indicates the code path exists in both the rapid-release and extended-support branches.

RemediationAI

Vendor-released patch: Firefox 151 and Firefox ESR 140.11 - upgrade to these exact versions or later, which is the definitive fix. Enterprises running Mozilla packages from Linux distributions should apply the corresponding distro updates, such as SUSE-SU-2026:2039 (https://www.suse.com/support/update/SUSE-SU-2026:2039/), and consult the Mozilla advisories at https://www.mozilla.org/security/advisories/mfsa2026-46/, mfsa2026-48, mfsa2026-50 and mfsa2026-51. Because exploitation requires the user to load malicious content, an effective interim compensating control is to restrict browsing to trusted sites and enforce update policies via enterprise configuration; where feasible, using strict content/URL filtering to block untrusted external sites reduces the chance a user reaches an exploit page, at the trade-off of reduced browsing freedom. There is no configuration toggle that disables the affected HTTP origin-validation logic without breaking normal networking, so patching is strongly preferred over any workaround.

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8.2

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-2026-8950 vulnerability details – vuln.today

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Mozilla Firefox CVE-2026-8950

Severity by source

CVSS VectorNVD

Lifecycle Timeline

DescriptionCVE.org

AnalysisAI

Technical ContextAI

RemediationAI

More in Mozilla

Same weakness CWE-346 – Origin Validation Error

Same technique Authentication Bypass

Vendor StatusVendor

SUSE

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External POC / Exploit Code