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Mozilla Firefox CVE-2026-16405

| EUVDEUVD-2026-46243 HIGH
Information Exposure (CWE-200)
2026-07-21 mozilla GHSA-cjjv-h8qx-pq7p
Information Disclosure Mozilla Suse Red Hat
High
Disputed · 7.5 Vendor: mozilla
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Severity by source

Sources disagree (Low–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 WebSocket disclosure with no auth, but realistic exploitation needs the victim to load attacker content, so UI:R; confidentiality-only impact means 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:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
SUSE
CRITICAL
qualitative
Red Hat
3.4 LOW
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

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 21, 2026 - 20:23 vuln.today
CVSS changed
Jul 21, 2026 - 20:22 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

Information disclosure in the Networking: WebSockets component. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13.

AnalysisAI

Information disclosure in Mozilla Firefox's Networking: WebSockets component allows remote attackers to read sensitive data across origin or trust boundaries without authentication or user interaction. The flaw affects Firefox releases prior to 153 and the ESR line prior to 140.13, and is corrected in those fixed builds. No public exploit identified at time of analysis, and the issue is not listed in CISA KEV, but the network-reachable, no-privilege CVSS 7.5 profile makes it a broad exposure across the very large Firefox install base.

Technical ContextAI

The vulnerability lives in Firefox's WebSocket networking stack (the ws:// / wss:// protocol implementation layered over HTTP upgrade). WebSockets provide full-duplex channels between browser and server and are subject to same-origin and mixed-content protections; a defect here can leak memory contents, cross-origin response data, or connection state that should be isolated. The affected CPE is cpe:2.3:a:mozilla:firefox:*, i.e. the desktop Firefox application generically. The CWE-200 classification (Exposure of Sensitive Information to an Unauthorized Actor) identifies the root-cause class as improper information exposure rather than memory corruption, consistent with the CVSS impact of high confidentiality but no integrity or availability effect.

RemediationAI

Vendor-released patch: upgrade to Firefox 153 or later on the mainline channel, and to Firefox ESR 140.13 or later on the extended-support channel, per Mozilla advisories MFSA2026-68 (https://www.mozilla.org/security/advisories/mfsa2026-68/) and MFSA2026-70 (https://www.mozilla.org/security/advisories/mfsa2026-70/). Enterprises should push the update through their managed-update mechanism (Firefox background updater, ESR policy, or software distribution) and confirm the running build reports 153+/140.13+. No official pre-patch workaround is published; as an interim compensating control you can restrict or block outbound WebSocket connections (ws:// and wss://) to untrusted destinations at the proxy or firewall, accepting that this will break legitimate real-time web applications (chat, live dashboards, collaborative editing) that depend on WebSockets, so it is a stopgap only until the browser is updated.

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Same weakness CWE-200 – Information Exposure

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Same technique Information Disclosure

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CVE-2015-1701 HIGH POC
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CVE-2014-6324 HIGH POC
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Vendor StatusVendor

SUSE

Severity: Critical
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected
SUSE Linux Enterprise Module for Desktop Applications 15 SP7 Affected

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CVE-2026-16405 vulnerability details – vuln.today
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