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Mozilla Firefox CVE-2026-100769

| EUVDEUVD-2026-88921 HIGH
Use After Free (CWE-416)
2026-09-29 mozilla GHSA-99h5-m2xx-wmr7
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 WebAssembly page
  2. Delivery
    Lure victim to visit URL
  3. Exploit
    Trigger use-after-free in JS/WASM engine
  4. Execution
    Corrupt content-process memory
  5. Impact
    Execute attacker-controlled code

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 actively browse to attacker-controlled web content that delivers a malicious WebAssembly payload to Firefox's JavaScript engine (UI:R in the vector). No authentication or special privileges are needed (PR:N), and it works against default Firefox configurations since WebAssembly is enabled by default. Limiting factors: the attack is client-side and cannot be triggered without user interaction (a page load), it affects only versions prior to Firefox 157 / ESR 153.4 / ESR 140.17, and because scope is unchanged the initial impact is confined to the content process unless combined with a separate sandbox-escape bug.
Impact

This is a genuine but not top-tier priority. The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H = 8.8 HIGH) reflects a classic client-side browser memory-corruption bug: network-reachable, low complexity, no privileges, but requiring user interaction (the victim must load a malicious page). A CWE-416 use-after-free in the JavaScript/WebAssembly engine is RCE-class, which justifies the C/I/A:H triad. However, exploitation signals are all soft: no EPSS score, no CISA KEV listing, and no public proof-of-concept were provided - Mozilla self-reported and self-patched this via its regular MFSA advisory batch. There is no evidence of active exploitation. Modern Firefox also runs content in a sandboxed process, and this bug is scope-unchanged (S:U), meaning a UAF here yields code execution in the content process, not a confirmed sandbox escape to the host - so real-world impact is bounded by the sandbox absent a chained escape. Net: real vulnerability worth patching promptly given Firefox's ubiquity, but no data indicates weaponization; treat as routine-urgent, not emergency.
Exploit ScenarioDerived

An attacker crafts a malicious web page containing specially-designed WebAssembly that triggers the use-after-free in Firefox's JS engine, then lures a victim to visit it (via phishing link, malvertising, or a compromised site). When the victim's browser processes the page, the freed-then-reused object corrupts memory, potentially giving the attacker code execution within the content process. No public exploit code was identified at time of analysis.
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 in Mozilla Firefox's JavaScript WebAssembly component lets remote attackers corrupt memory and potentially achieve code execution or disclose sensitive data when a user loads attacker-controlled web content containing a malicious WebAssembly payload. The flaw affects default Firefox configurations up to Firefox 157 and the ESR branches-Firefox ESR 153.4 and Firefox ESR 140.17 are the first fixed releases-and requires no authentication, only that the victim browse a crafted page (CVSS 3.1: 8.8, AV:N/AC:L/PR:N/UI:R). No public exploit code has been identified at time of analysis and the issue is not in CISA KEV, making this a genuine but not top-tier priority; exploitation is client-side and requires user interaction, and because scope is unchanged the initial impact is confined to the content process unless chained with a separate sandbox-escape bug.

RemediationAI

Vendor-released patch: upgrade to Firefox 157, Firefox ESR 153.4, or Firefox ESR 140.17-any of these builds contains the fix for the WebAssembly use-after-free, with details in Mozilla advisories MFSA 2026-100, MFSA 2026-99 and MFSA 2026-97 (fix discussion at https://bugzilla.mozilla.org/show_bug.cgi?id=2067190). Enterprise fleets should prioritize the ESR channels, since ESR 140.17 covers long-term deployments that cannot move to 157 immediately, and should keep automatic updates enabled so the patched build is applied without relying on manual user action. If an immediate upgrade is not possible, the only meaningful compensating control is to remove the attack surface by setting javascript.options.wasm to false in about:config (or through enterprise policy), which blocks WebAssembly execution in the vulnerable builds-though this breaks WebAssembly-based web applications and is not a substitute for patching. Because exploitation requires the victim to load attacker-controlled content and scope remains unchanged, restricting browsing to trusted sites and relying on content-process sandboxing and site isolation reduces-but does not eliminate-risk while patching is staged.

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Technical ContextAI · show details

The root cause is a use-after-free (CWE-416) in the JavaScript: WebAssembly component-the engine code that parses, validates, compiles and manages the lifetime of WebAssembly modules inside Firefox's JavaScript engine. Because WebAssembly is enabled by default in all supported desktop Firefox builds, an attacker can deliver a crafted .wasm module or supporting JavaScript from an ordinary web page; a freed object is then reused while still referenced, producing memory corruption that can be steered toward arbitrary code execution or, as the 'Information Disclosure' tag indicates, leakage of memory contents. The CPE record cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* is a broad wildcard reflecting that all branch lines below the fixed builds are potentially affected rather than a single version. The harvested tags (Use After Free, Memory Corruption, Information Disclosure, Mozilla) align with the CVSS 3.1 vector AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H, which rates high confidentiality and integrity impact but leaves scope unchanged-meaning the corruption is contained within the Firefox content process unless paired with a second, separate sandbox-escape vulnerability.

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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

Network-delivered malicious page (AV:N), no privileges (PR:N) but victim must load content (UI:R); UAF memory corruption yields RCE-class C/I/A:H within the unchanged-scope content process.

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 MEDIUM
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 - 12:36 cve.org
UNKNOWN (no severity yet)
CVE Published
Sep 29, 2026 - 12:36 cve.org
HIGH 8.8

DescriptionCVE.org

Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, and Firefox ESR 140.17.

Executive ViewAI

Why It Matters

Mozilla Firefox is widely deployed across corporate endpoints, and a memory-corruption flaw in its JavaScript WebAssembly engine (CVE-2026-100769, CVSS 8.8) could allow attacker-controlled web content to run code or expose sensitive data on any employee's machine as a normal part of web browsing. No public exploit code has been identified at time of analysis and the issue is not in CISA KEV, and because the browser's sandbox keeps the initial impact inside the content process unless chained with a separate sandbox-escape flaw, this is a broad-exposure remediation priority rather than an emergency. Leadership should care because the affected population is essentially every Firefox user, the trigger is routine browsing, and remediation is tied to specific Firefox ESR builds that must be tracked to closure.

Business Impact: High
Compensating Controls

Apply vendor patch (Firefox ESR 153.4 / Firefox ESR 140.17); where upgrade is delayed, restrict or disable WebAssembly execution via Firefox enterprise policy, enforce site isolation, and constrain high-risk users to vetted web content until rebuilt browsers are in place.

Threat Intelligence Overview

EPSS Score
0.3%
Top 76% exploitable
Prevalence
Ubiquitous
Firefox is one of the most widely deployed desktop browsers worldwide
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 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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Vendor StatusVendor

SUSE

Severity: Moderate
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-2026-100769 ADVISORY https://vuldb.com/vuln/411337 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2067190 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/mfsa2026-99/

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