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Mozilla Firefox CVE-2026-100770

| EUVDEUVD-2026-88922 CRITICAL
Use After Free (CWE-416)
2026-09-29 mozilla GHSA-cm7f-mvvg-gwpr
Information Disclosure Use After Free Memory Corruption Red Hat Mozilla Firefox
9.6
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
    Victim visits attacker-controlled page
  2. Delivery
    Page triggers UAF in DOM Content Processes
  3. Exploit
    Reclaim freed object to corrupt memory
  4. Execution
    Escape content sandbox to parent process
  5. Impact
    Execute code with browser privileges

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

Exploitation requires the victim to load attacker-controlled web content in Firefox (UI:R) that triggers the use-after-free in the DOM Content Processes component; no authentication is needed (PR:N) and the attack is network-delivered (AV:N). Limiting factors: it needs user interaction (visiting/rendering a malicious page), affects only unpatched Firefox before 157 / ESR 153.4 / ESR 140.17 / ESR 115.42, and reliable exploitation must defeat Firefox's multi-process content sandbox to reach the parent process - the scope change (S:C) is precisely this sandbox escape. No non-default configuration is required.
Impact

This is a genuinely high-severity issue by construction: the CVSS 9.6 is driven by S:C (scope change), reflecting a use-after-free in Firefox's DOM Content Processes that escapes the content sandbox and impacts the more-privileged parent process - hence C:H/I:H/A:H. The vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R is network-reachable and unauthenticated but requires user interaction (UI:R), i.e., the victim must visit or render attacker-controlled web content. Countervailing signals lower the *real-world urgency*: there is no EPSS score, no CISA KEV listing, and no public POC provided; Mozilla self-reported this and its advisories carry no indication of in-the-wild exploitation. UAF sandbox escapes are RCE-class and attractive to exploit developers, but weaponizing them reliably is non-trivial (memory grooming, defeating content-sandbox and parent-process mitigations). No signals conflict materially - the CVSS reflects worst-case technical impact while exploitation-likelihood signals (EPSS/KEV/POC all absent) suggest this is not yet under active or widespread exploitation. Note the tag set labels this 'Information Disclosure,' which understates a memory-corruption sandbox escape with full C/I/A:H.
Exploit ScenarioDerived

An attacker hosts a malicious web page (or injects malicious content into a page the victim loads, e.g., via a compromised ad) that triggers the use-after-free in the DOM Content Processes component when rendered. Chaining the freed-object reuse into controlled memory corruption, the attacker escapes the content sandbox to execute code in the more-privileged parent process. No public POC or active exploitation is identified at time of analysis.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
No patch listed yet 0.3% exploitation probability (EPSS)

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AnalysisAIv1 – Sep 29, 2026

Mozilla Firefox can be driven to escape its content sandbox through a use-after-free in the DOM Content Processes component, letting a remote, unauthenticated attacker who convinces a victim to load a crafted page (UI:R, PR:N) corrupt memory in the sandboxed content process and cross into the more privileged parent process - the pivot reflected in the CVSS 9.6 scope-change rating and the C:H/I:H/A:H metrics. The flaw affects Firefox before 157 and the ESR trains before 153.4, 140.17 and 115.42, and it is fixed in those exact builds. No confirmed active exploitation (CISA KEV) and no public exploit code were identified at time of analysis.

RemediationAI

Vendor-released patch: upgrade to Firefox 157, Firefox ESR 153.4, Firefox ESR 140.17 or Firefox ESR 115.42; hosts still on the ESR 115 line should migrate to a newer ESR branch where possible, since 115.42 is the last-stop fix on a legacy train. Version details are documented in Mozilla's advisories at https://www.mozilla.org/security/advisories/mfsa2026-100/, https://www.mozilla.org/security/advisories/mfsa2026-97/, https://www.mozilla.org/security/advisories/mfsa2026-98/ and https://www.mozilla.org/security/advisories/mfsa2026-99/, with the underlying defect tracked at https://bugzilla.mozilla.org/show_bug.cgi?id=2068322; verify the installed version via Help > About Firefox and ensure automatic updates are enabled. Because the assessment states no non-default configuration is needed to trigger the flaw, there is no supported settings-based workaround that restores the sandbox boundary: disabling JavaScript or restricting scripting to trusted sites removes the most direct trigger but breaks most legitimate web applications and is an incomplete mitigation given the DOM attack surface, and host-level sandboxing or endpoint hardening outside Firefox does not fix an in-browser content-process escape. Treat patch deployment as the only reliable fix, and prioritize internet-facing and ESR endpoints accordingly.

Affects your stack

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Technical ContextAI · show details

The root cause is CWE-416 (use-after-free) in the DOM Content Processes component, the part of Firefox's multi-process (Electrolysis) architecture that renders web content inside a sandboxed child process separate from the browser parent. Freeing a DOM object while a live reference remains allows the attacker to reallocate and reuse that memory, producing memory corruption and, per the associated tags, potential information disclosure. Because the corruption occurs in a sandboxed content process, a working exploit can pivot out of the sandbox and affect the higher-privileged parent process, which is exactly what the CVSS S:C (scope change) metric captures alongside C:H/I:H/A:H. CPE data (cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*) confirms the affected package is Mozilla Firefox itself across both rapid-release and ESR channels, the issue is tracked as EUVD-2026-88922, and the references point to Mozilla bug 2068322 plus the MFSA advisories mfsa2026-100, mfsa2026-97, mfsa2026-98 and mfsa2026-99.

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Severity by source

Vendor (mozilla) PRIMARY 9.6 CRITICAL
AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
vuln.today AI 9.6 CRITICAL

Network-delivered malicious page (AV:N/PR:N) requiring a victim to render it (UI:R); the content-sandbox escape crosses a privilege boundary (S:C) yielding full C/I/A impact.

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 7.5 HIGH

Primary rating from Vendor (mozilla).

CVSS VectorVendor: mozilla

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

3
CVSS changed
Sep 29, 2026 - 17:22 NVD
9.6 (CRITICAL)
CVE Published
Sep 29, 2026 - 12:36 cve.org
UNKNOWN (no severity yet)
CVE Published
Sep 29, 2026 - 12:36 cve.org
CRITICAL 9.6

DescriptionCVE.org

Sandbox escape due to use-after-free in the DOM: Content Processes component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.

Articles & Coverage 1

News Critical UAF Sandbox Escape in Mozilla Firefox - CVE-2026-100770 Sep 30, 2026

Executive ViewAI

Why It Matters

A critical sandbox-escape vulnerability in Mozilla Firefox (CVE-2026-100770, CVSS 9.6) lets a remote, unauthenticated attacker who convinces a user to open a crafted web page corrupt memory in the sandboxed content process and cross into the browser's more privileged parent process. Because the flaw is rated critical with a scope change and affects every Firefox build before 157 and the ESR trains before 153.4, 140.17 and 115.42, any employee browsing the web on an unpatched install - including long-support ESR deployments common on managed endpoints - is a potential path to full workstation compromise. The attacker needs no credentials and only a single user click, so leadership should treat this as a workforce-wide endpoint exposure rather than an isolated browser defect.

Business Impact: Severe
Compensating Controls

Apply vendor patch (Firefox 157; ESR 153.4, 140.17, 115.42), verifying version guidance directly against Mozilla's advisory given the patch status inconsistency in this record. Until those builds are deployed, restrict affected users to a hardened alternative browser for general web and email link handling, enforce network-level and DNS-layer blocking of untrusted or newly registered domains, maintain endpoint detection coverage for browser child-process anomalies and unexpected parent-process memory activity, and reduce reliance on Firefox for high-value administrative or privileged work.

Threat Intelligence Overview

EPSS Score
0.3%
Top 75% exploitable
Prevalence
Ubiquitous
Firefox is one of the most widely deployed desktop web browsers globally
Data Quality
7 sources
Confidence: High
EUVD 🇯🇵JVN 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 CRITICAL
CISA KEV No
Public POC No
EPSS 0.3%
Patch available No
Active threat No
Deciding rule
CRITICAL severity
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
Very High
Technical Impact
Total

Priority Score

48
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +48
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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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-2026-100770 ADVISORY https://vuldb.com/vuln/411324 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2068322 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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