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Mozilla Firefox CVE-2026-16399

| EUVDEUVD-2026-46237 HIGH
Origin Validation Error (CWE-346)
2026-07-21 mozilla GHSA-9rrq-xqwp-wx9r
Mozilla Information Disclosure Red Hat
High
Disputed · 7.5 Vendor: mozilla
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Severity by source

Sources disagree (Medium–Critical)
Vendor (mozilla) PRIMARY
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
vuln.today AI
6.5 MEDIUM

Network-reachable with no auth, but a browser bug realistically needs the victim to load hostile content, so UI:R; impact is cross-origin data disclosure only, hence C:H and I/A:N.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/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
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 VectorVendor: mozilla

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

Lifecycle Timeline

4
Analysis Generated
Jul 22, 2026 - 19:06 vuln.today
CVSS changed
Jul 22, 2026 - 18:22 NVD
7.5 (HIGH)
CVE Published
Jul 21, 2026 - 12:38 cve.org
UNKNOWN (no severity yet)
CVE Published
Jul 21, 2026 - 12:38 cve.org
HIGH 7.5

DescriptionCVE.org

Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 153.

AnalysisAI

Cross-origin information disclosure in Mozilla Firefox's DOM: Navigation component allows a malicious web page to bypass site isolation (Fission) boundaries and read data belonging to another origin. The flaw affects Firefox versions prior to 153 and is remotely reachable over the network with no privileges required, though impact is limited to confidentiality. There is no public exploit identified at time of analysis and EPSS exploitation probability is low (0.13%).

Technical ContextAI

The vulnerability lives in Firefox's navigation handling within the DOM engine and undermines site isolation, Mozilla's process-per-site 'Fission' architecture that keeps content from different origins in separate processes so one site cannot observe another's data. The root cause maps to CWE-346 (Origin Validation Error): during a navigation the browser fails to correctly validate or enforce the origin boundary, so content from one site can gain access to state or responses that should be walled off by the same-origin policy. The affected component is the shared Gecko/Firefox codebase (CPE cpe:2.3:a:mozilla:firefox:*), meaning all channels built on the pre-153 engine are in scope.

RemediationAI

Vendor-released patch: Firefox 153 - upgrade all Firefox installations to version 153 or later, the definitive remediation per Mozilla Security Advisory MFSA2026-68 (https://www.mozilla.org/security/advisories/mfsa2026-68/). For managed fleets, push the update through your existing browser management/auto-update channel and verify ESR users are moved to a fixed ESR build once Mozilla confirms one. No specific configuration workaround is published; as an interim compensating control you can restrict browsing to trusted sites or deploy web filtering/proxy blocking of untrusted content to reduce the chance a user loads a malicious page, at the cost of usability - this only lowers exposure and does not close the flaw. See Bugzilla bug 2049981 (https://bugzilla.mozilla.org/show_bug.cgi?id=2049981) for technical tracking.

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Same weakness CWE-346 – Origin Validation Error

View all
CVE-2015-4495 HIGH POC
8.8
CVE-2025-34291 CRITICAL POC
9.4
CVE-2020-16952 HIGH POC
8.6
CVE-2022-50925 CRITICAL POC
9.8
CVE-2024-25124 CRITICAL POC
9.8
CVE-2023-29711 CRITICAL POC
9.8
CVE-2023-33443 CRITICAL POC
9.8
CVE-2023-29728 CRITICAL POC
9.8

Same technique Information Disclosure

View all
CVE-2019-2725 CRITICAL POC
9.8
CVE-2021-34523 CRITICAL POC
9.0
CVE-2013-2251 CRITICAL POC
9.8
CVE-2017-5638 CRITICAL POC
9.8
CVE-2025-24813 CRITICAL POC
9.8
CVE-2015-1701 HIGH POC
7.8
CVE-2017-0147 HIGH POC
7.5
CVE-2014-6324 HIGH POC
8.8

Vendor StatusVendor

SUSE

Severity: Critical
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Desktop Applications 15 SP7 Affected
SUSE Linux Enterprise Module for Package Hub 15 SP7 Affected

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CVE-2026-16399 vulnerability details – vuln.today
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