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Mozilla Firefox CVE-2026-100757

| EUVDEUVD-2026-88909 HIGH
Use After Free (CWE-416)
2026-09-29 mozilla GHSA-q9fp-c34q-3gpp
Information Disclosure Use After Free Memory Corruption Red Hat Mozilla Firefox
8.8
CVSS 3.1 · Vendor: mozilla
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Attack ChainAIDerived

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

  1. Access
    Host malicious web page
  2. Delivery
    Victim visits page in Firefox
  3. Exploit
    Trigger use-after-free in Widget component
  4. Execution
    Corrupt heap to control freed object
  5. Impact
    Execute code in content process

Vulnerability Assessment

Weakness
CWE
CWE-416
ASVS 5.0
V15 - Secure Coding and Architecture Memory lifecycle management
MITRE ATT&CK

2 techniques across 2 tactics: Execution, 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

Requires the victim to open or render attacker-controlled web content in a vulnerable Firefox build (versions before Firefox 157, ESR 153.4, ESR 140.17, or ESR 115.42) - the UI:R user-interaction requirement is the key limiter. No authentication, no special browser configuration, and no non-default settings are needed; the flaw is in the standard Widget rendering path. Exploitation is bounded to a single vulnerable-client-at-a-time model (no server-side mass exploitation) and requires reliable heap manipulation to weaponize the use-after-free.
Impact

This is a client-side use-after-free (CWE-416) in Firefox's Widget component, scored CVSS 8.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H) by the reporter Mozilla. The vector indicates network reachability with low complexity and no privileges, but UI:R means a victim must actively interact (visit/render a malicious page), which is the primary limiting factor rather than any authentication or configuration barrier. UAF in a browser rendering-path component is RCE-class (full C/I/A:H within the content process, S:U). However, exploitation signals temper urgency: there is no EPSS score, no CISA KEV listing, and no public proof-of-concept in the provided data - status is 'no public exploit identified at time of analysis.' Mozilla's advisories (MFSA2026-97/98/99/100) are self-reported vendor disclosures with no independent SSVC/automatable determination supplied. Net: a genuinely high-impact memory-corruption bug in ubiquitous software that warrants prompt patching, but with no evidence of active or automated exploitation it is a routine-priority browser update rather than an emergency. One data note: the CVSS is vendor-assigned, not NVD-analyzed, so treat the 8.8 as reporter self-scoring.
Exploit ScenarioDerived

An attacker crafts a malicious web page that manipulates Firefox's Widget component to trigger a use-after-free, then lures a victim into visiting it (UI:R). Successful heap grooming turns the dangling-pointer condition into arbitrary code execution in the browser content process. No public PoC or exploit code is identified in the available data.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
No patch listed yet 0.3% exploitation probability (EPSS)

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AnalysisAIv1 – Sep 29, 2026

Use-after-free (CWE-416) in Mozilla Firefox's Widget component allows remote attackers to potentially execute arbitrary code when a victim renders attacker-controlled web content in unpatched versions (before Firefox 157, Firefox ESR 153.4, ESR 140.17, or ESR 115.42). Successful exploitation requires reliable heap manipulation and depends on the user opening malicious content (UI:R), but can achieve high confidentiality, integrity, and availability impact. No public exploit identified at time of analysis.

RemediationAI

Upgrade to the fixed versions: Firefox 157, Firefox ESR 153.4, Firefox ESR 140.17, or Firefox ESR 115.42, as specified in Mozilla security advisories mfsa2026-97, mfsa2026-98, mfsa2026-99, and mfsa2026-100 (see https://www.mozilla.org/security/advisories/mfsa2026-100/ and https://bugzilla.mozilla.org/show_bug.cgi?id=2049352). No specific workaround is documented, but because exploitation requires user interaction (UI:R), reducing exposure by blocking untrusted web content, enforcing script blockers where feasible, and keeping automatic updates enabled for all Firefox and ESR installations can lower risk until patching is complete. Trade-offs: disabling JavaScript may break legitimate sites and does not fully eliminate the underlying memory-safety flaw.

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Technical ContextAI · show details

This is a use-after-free (CWE-416) in the Widget component of Mozilla Firefox, which provides the cross-platform abstraction for native UI elements and event handling. The flaw occurs when a widget object is freed while a reference to it remains, allowing an attacker who controls web content to trigger a dangling-pointer dereference during rendering or event processing. The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H) indicates the attack is network-delivered and unauthenticated, but requires user interaction (UI:R) - typically the victim loading a malicious page. The issue is in the standard rendering path, so no special browser configuration or non-default settings are needed. The CPE cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* confirms all Firefox versions are in scope, with fixes limited to the versions listed in Mozilla advisories mfsa2026-97 through mfsa2026-100 and tracked in bug 2049352.

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Severity by source

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 8.8 HIGH

Remotely reachable via malicious web content (AV:N) requiring only a page visit (UI:R, PR:N); a UAF yields content-process code execution with full C/I/A impact, scope unchanged.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/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:N/SI:N/SA:N
SUSE CRITICAL
Red Hat 7.5 HIGH

Primary rating from Vendor (mozilla).

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

2
CVE Published
Sep 29, 2026 - 12:35 cve.org
HIGH 8.8
CVE Published
Sep 29, 2026 - 12:35 cve.org
UNKNOWN (no severity yet)

DescriptionCVE.org

Use-after-free in the Widget component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.

Executive ViewAI

Why It Matters

An unpatched memory-safety defect in Mozilla Firefox's Widget component could allow an attacker to run malicious code on an employee's workstation after the user simply opens a crafted web page. Because Firefox is broadly deployed across the workforce and this affects confidentiality, integrity, and availability simultaneously, a single successful compromise could expose corporate data, permit tampering, or disrupt endpoint availability. Leadership should treat browser remediation as a time-bound operational priority rather than routine maintenance.

Business Impact: High
Compensating Controls

Apply vendor patch.

Threat Intelligence Overview

EPSS Score
0.3%
Top 75% exploitable
Prevalence
Ubiquitous
Firefox is a mainstream browser deployed across consumer and enterprise environments worldwide
Data Quality
7 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment 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 0.3%
Patch available No
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
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
No
Human Impact
High
Technical Impact
Total

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

Use After Free HIGH

Use-after-free vulnerabilities occur when a program continues to access memory through a pointer after that memory has been deallocated.

Memory Corruption HIGH

Memory corruption occurs when a program writes data beyond the boundaries of allocated memory regions or accesses memory in unintended ways, violating the integrity of the process's address space.

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

Affected Products (CPE)CVE.org

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

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Same weakness CWE-416 – Use After Free

View all
CVE-2019-0708 CRITICAL POC
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CVE-2014-0322 HIGH POC
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CVE-2012-4792 HIGH POC
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CVE-2009-4324 HIGH POC
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CVE-2015-0313 CRITICAL POC
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CVE-2015-5122 CRITICAL POC
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CVE-2013-2551 HIGH POC
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Same technique Information Disclosure

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CVE-2021-34523 CRITICAL POC
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CVE-2013-2251 CRITICAL POC
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CVE-2017-5638 CRITICAL POC
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CVE-2025-24813 CRITICAL POC
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CVE-2025-68613 HIGH POC
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CVE-2015-1701 HIGH POC
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CVE-2017-0147 HIGH POC
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Vendor StatusVendor

SUSE

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

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-100757 ADVISORY https://vuldb.com/vuln/411327 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2049352 REF https://www.mozilla.org/security/advisories/mfsa2026-100/ REF https://www.mozilla.org/security/advisories/mfsa2026-101/ REF https://www.mozilla.org/security/advisories/mfsa2026-102/ REF https://www.mozilla.org/security/advisories/mfsa2026-103/ REF https://www.mozilla.org/security/advisories/mfsa2026-97/ REF https://www.mozilla.org/security/advisories/mfsa2026-98/ REF https://www.mozilla.org/security/advisories/mfsa2026-99/

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