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Mozilla Firefox CVE-2026-16371

| EUVDEUVD-2026-46207 HIGH
Improper Privilege Management (CWE-269)
2026-07-21 mozilla GHSA-8rfc-phx9-6vc2
Privilege Escalation Mozilla
High
Disputed · 8.8 Vendor: mozilla
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Lure user to malicious page
  2. Delivery
    Deliver crafted DOM navigation
  3. Exploit
    Abuse improper privilege management
  4. Execution
    Escape privilege boundary
  5. Impact
    Gain elevated access on host

Vulnerability Assessment

Weakness
CWE
CWE-269
OWASP Top 10:2025
A06:2025 - Insecure Design
ASVS 5.0
V8 - Authorization Least privilege enforcement
MITRE ATT&CK

1 technique across 1 tactic: Privilege Escalation

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

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Exploitation Conditions

The vulnerability is in the DOM Navigation component, so exploitation requires the victim's Firefox (versions before 153, or ESR before 140.13) to process attacker-controlled navigation - typically by loading a malicious web page or resource. The supplied CVSS vector lists UI:N (no user interaction) and S:U (no scope change), but for a browser navigation flaw realistic exploitation almost certainly requires the user to visit or be redirected to attacker content, which limits fully unattended remote exploitation; this discrepancy between the CVSS vector and the browser-client nature of the bug should be verified against Mozilla's advisory (mfsa2026-68 / mfsa2026-70). Limiting factors: the target must run an unpatched Firefox/ESR build and must be induced to load hostile content.
Impact

Signals conflict and should be weighed carefully. The provided CVSS 3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) implies trivially exploitable, unauthenticated remote full compromise - however, this rating is unusual for a browser privilege-escalation bug, which typically requires the victim to visit a malicious page (UI:R) and usually results in a scope change (S:C) when escaping the content process. The absence of UI:R and S:C in the supplied vector is suspect and should be verified against Mozilla's advisory. Countering the high CVSS, the EPSS score is very low (0.15%, 5th percentile), there is no CISA KEV listing (not actively exploited) and no public exploit code identified, indicating this is not currently a widespread or weaponized threat. Net assessment: a genuinely serious client-side flaw in ubiquitous software that warrants prompt patching, but the real-world urgency is moderated by the lack of exploitation evidence and by the practical requirement that a user load attacker-controlled web content.
Exploit ScenarioDerived

An attacker hosts or injects malicious web content and lures a Firefox user to load it (for example via a link, ad, or compromised site); the page abuses the DOM Navigation flaw to escape its intended privilege boundary and gain elevated access on the victim's browser. Given the low attack complexity indicated by the CVSS vector, exploitation would be reliable once a working technique exists, but no public exploit code has been identified at time of analysis.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.1% exploitation probability (EPSS)

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AnalysisAIv1 – Jul 22, 2026

Privilege escalation in Mozilla Firefox's DOM Navigation component allows remote attackers to elevate privileges, and given the CVSS network vector (AV:N/PR:N/UI:N) an attacker could compromise confidentiality, integrity, and availability without authentication or user interaction. The flaw affects Firefox before version 153 and Firefox ESR before 140.13, and was fixed by Mozilla in those releases. No public exploit identified at time of analysis, and EPSS exploitation probability is low (0.15%, 5th percentile).

RemediationAI

Vendor-released patch: upgrade to Firefox 153 or Firefox ESR 140.13, which contain the fix. Standard-channel users should update to Firefox 153 (or later) and enterprise/LTS deployments should move to ESR 140.13 (or later); verify deployment via the Mozilla advisories at https://www.mozilla.org/security/advisories/mfsa2026-68/ and https://www.mozilla.org/security/advisories/mfsa2026-70/. Because Firefox auto-updates by default, ensure automatic updates are enabled and not blocked by managed policy; where immediate patching is not possible, compensating controls include restricting browsing to trusted sites, deploying network/proxy-level web filtering to reduce exposure to untrusted content, and enforcing site isolation - though these reduce rather than eliminate risk and may impair usability, so patching remains the only complete remedy.

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Technical ContextAI · show details

The vulnerability resides in the DOM Navigation component of Gecko, Firefox's browser engine, which governs how documents transition between browsing contexts (loading URLs, history traversal, and cross-origin navigations). The root cause class is CWE-269 (Improper Privilege Management), meaning the component fails to correctly assign, enforce, or drop the privilege boundary associated with a navigation, potentially allowing web content to gain privileges it should not hold (e.g., escaping the content sandbox or crossing an origin/principal boundary). The affected product per CPE is cpe:2.3:a:mozilla:firefox (all versions prior to the fix), and the same engine underlies the ESR channel used in enterprise and Linux distribution deployments.

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Severity by source

Sources disagree (Medium–Critical)
Vendor (mozilla) PRIMARY 8.8 HIGH
AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
vuln.today AI 9.6 CRITICAL

Browser navigation flaws require the victim to load attacker content (UI:R) and privilege escalation escaping the content sandbox constitutes a scope change (S:C); impact is high across C/I/A.

3.1 AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
SUSE CRITICAL
Red Hat 6.1 MEDIUM

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
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

5
Severity Changed
Jul 24, 2026 - 21:22 NVD
CRITICAL HIGH
CVSS changed
Jul 24, 2026 - 21:22 NVD
9.8 (CRITICAL) 8.8 (HIGH)
CVSS changed
Jul 22, 2026 - 16:22 NVD
9.8 (CRITICAL)
CVE Published
Jul 21, 2026 - 12:37 cve.org
UNKNOWN (no severity yet)
CVE Published
Jul 21, 2026 - 12:37 cve.org
CRITICAL 9.8

DescriptionCVE.org

Privilege escalation in the DOM: Navigation component. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13.

Executive ViewAI

Why It Matters

Mozilla Firefox versions before 153 contain a critical privilege escalation vulnerability that allows remote attackers to gain complete control of users' systems without any authentication or user interaction requirements. No public exploits have been identified at this time, but the attack's ease and critical severity put all organizations with Firefox deployments at significant risk for data theft, credential compromise, and malware infection. Immediate patching across all endpoints is required.

Business Impact: Severe
Compensating Controls

Apply vendor patch: Firefox 153, Firefox ESR 140.13

Threat Intelligence Overview

EPSS Score
0.1%
Top 95% exploitable
Prevalence
Ubiquitous
Firefox is one of the most widely deployed web browsers worldwide
Data Quality
6 sources
Confidence: High
EUVD NVD CVE.org EPSS Vendor VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.1%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
No
Human Impact
Very High

Priority Score

44
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +44
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Privilege Escalation HIGH

Privilege escalation occurs when an attacker leverages flaws in access control mechanisms to gain permissions beyond what they were originally granted.

Affected Products (CPE)CVE.org

cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*

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Same weakness CWE-269 – Improper Privilege Management

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9.8
CVE-2019-1405 HIGH POC
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Same technique Privilege Escalation

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CVE-2024-0012 CRITICAL POC
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CVE-2025-47812 CRITICAL POC
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CVE-2013-0422 CRITICAL POC
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CVE-2013-0632 CRITICAL POC
9.8
CVE-2024-9474 MEDIUM POC
6.9

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

References

Advisories & patches
ADVISORY https://access.redhat.com/errata/RHSA-2026:47101 ADVISORY https://access.redhat.com/errata/RHSA-2026:47105 ADVISORY https://vuldb.com/vuln/380872 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2008369 REF https://www.mozilla.org/security/advisories/mfsa2026-68/ REF https://www.mozilla.org/security/advisories/mfsa2026-70/ REF https://www.mozilla.org/security/advisories/mfsa2026-71/ REF https://www.mozilla.org/security/advisories/mfsa2026-72/ REF https://www.mozilla.org/security/advisories/mfsa2026-84/ REF https://www.mozilla.org/security/advisories/mfsa2026-87/

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