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Mozilla Firefox CVE-2026-74936

| EUVDEUVD-2026-60745 CRITICAL
Use After Free (CWE-416)
2026-08-18 mozilla GHSA-m682-v78f-8q4j
Information Disclosure Use After Free Memory Corruption Red Hat Mozilla Suse
9.8
CVSS 3.1 · NVD
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Attack ChainAIDerived

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

  1. Access
    Lure victim to malicious page
  2. Delivery
    Serve crafted JS/WebAssembly module
  3. Exploit
    Trigger use-after-free in Wasm engine
  4. Execution
    Reclaim freed memory with controlled data
  5. Impact
    Execute code or leak memory 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

Exploitation requires the victim to load attacker-controlled web content that executes malicious WebAssembly in the affected Firefox/ESR build - i.e. the JavaScript/Wasm engine must process the crafted module, which happens by default whenever the user browses to the page. Limiting factors: the victim must actually visit or render the malicious content (user interaction in practice, despite the input vector stating UI:N), the browser must be an unpatched version below Firefox 154 / ESR 140.14 / ESR 153.1, and code execution is initially confined to the sandboxed content process, requiring a further sandbox escape for full host compromise. No authentication is needed (PR:N).
Impact

The input CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N, C:H/I:H/A:H = 9.8) treats this as unauthenticated remote code execution with no user interaction, but that conflicts with how a browser Wasm bug is actually triggered: exploitation realistically requires the victim to visit or render attacker-controlled content, i.e. UI:R - this discrepancy should be reconciled with the Mozilla advisory before treating the 9.8 as literal. Countervailing signals are notably low real-world exploitation indicators: EPSS is 0.16% (5th percentile), the CVE is not in CISA KEV, and no public POC is referenced, so there is no evidence of active or imminent mass exploitation. That said, Firefox's enormous install base and the historical reliability of Wasm/JS-engine UAFs as exploit primitives mean any operator running affected builds should patch promptly rather than deprioritize on the low EPSS alone; the low probability reflects absence-of-evidence, not proven safety.
Exploit ScenarioDerived

An attacker hosts a malicious web page containing crafted JavaScript and WebAssembly that manipulates object lifetimes to trigger the use-after-free, then lures a victim to visit it (or serves it via a malvertising frame). Reclaiming the freed memory with controlled data lets the attacker corrupt the heap to leak sensitive memory or execute code in the content process. No public POC is currently identified, and the network attack vector with low complexity makes exploitation feasible if a reliable primitive is developed.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.2% exploitation probability (EPSS)

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AnalysisAIv1 – Aug 20, 2026

Memory-corruption via a use-after-free in Firefox's JavaScript WebAssembly engine allows a remote attacker to corrupt heap memory and potentially achieve arbitrary code execution or information disclosure when a victim loads attacker-controlled content. All Firefox versions prior to Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1 are affected. There is no public exploit identified at time of analysis, KEV does not list it as actively exploited, and EPSS is low (0.16%), so this is a high-severity but not yet demonstrably-exploited flaw.

RemediationAI

Upgrade to a fixed build: Firefox 154, Firefox ESR 140.14, or Firefox ESR 153.1 (Vendor-released patch: Firefox 154 / ESR 140.14 / ESR 153.1), per the Mozilla Foundation Security Advisories at https://www.mozilla.org/security/advisories/mfsa2026-74/ and the related mfsa2026-76 through mfsa2026-80 pages. Because Firefox auto-updates by default, confirm managed/enterprise deployments have not pinned an older version and force the update through your management tooling. As an interim compensating control where patching lags, disabling WebAssembly by setting javascript.options.wasm to false in about:config removes the vulnerable execution path at the cost of breaking sites that rely on Wasm; more broadly restricting JavaScript on untrusted sites reduces exposure but degrades usability, so treat these only as short-term mitigations until the update is applied.

Affects your stack

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Technical ContextAI · show details

The flaw is a CWE-416 use-after-free in the WebAssembly (Wasm) subsystem of SpiderMonkey, Firefox's JavaScript/Wasm engine. WebAssembly executes untrusted low-level bytecode delivered by any visited web page, giving an attacker a rich, attacker-controlled surface for manipulating object lifetimes; a use-after-free arises when the engine continues to reference a heap object after it has been freed, letting an attacker reallocate that memory with controlled data and hijack pointers or type information. The affected component is delivered in the mozilla:firefox product (cpe:2.3:a:mozilla:firefox:*), and the tags (Memory Corruption, Use After Free, Information Disclosure) align with the typical impact spectrum of such bugs, ranging from info leak to full renderer compromise.

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Severity by source

NVD PRIMARY 9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
vuln.today AI 8.8 HIGH

Network-delivered via web content with low complexity and no privileges, but triggering requires the victim to visit malicious content, so UI:R; full memory-safety impact yields C/I/A:H within the content process (S:U).

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 7.5 HIGH
AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Red Hat 7.5 HIGH

Primary rating from NVD.

CVSS VectorNVD

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

Lifecycle Timeline

3
CVSS changed
Aug 20, 2026 - 20:52 NVD
9.8 (CRITICAL)
CVE Published
Aug 18, 2026 - 12:23 nvd
CRITICAL 9.8
CVE Published
Aug 18, 2026 - 12:23 cve.org
UNKNOWN (no severity yet)

DescriptionNVD

Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1.

Executive ViewAI

Why It Matters

Firefox versions prior to 154, Firefox ESR prior to 140.14, and Firefox ESR prior to 153.1 contain a critical memory-corruption vulnerability (CVE-2026-74936) enabling remote code execution when users visit attacker-controlled websites; no public exploit identified at time of analysis. This affects all employees and customers using vulnerable Firefox versions, potentially compromising workstations and enabling data exfiltration or lateral movement. Immediate browser patching is essential to close this attack vector.

Business Impact: High
Compensating Controls

Apply vendor patch.

Threat Intelligence Overview

EPSS Score
0.2%
Top 95% exploitable
Prevalence
Ubiquitous
one of the most widely deployed desktop web browsers globally
Data Quality
5 sources
Confidence: Medium
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 CRITICAL
CISA KEV No
Public POC No
EPSS 0.2%
Patch available Yes
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· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact
High

Priority Score

49
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +49
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)NVD

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-2015-5119 CRITICAL 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
7.5

Vendor StatusVendor

SUSE

Severity: Important
Product Status
Container suse/kiosk/firefox-esr:140.14-75.12 Affected
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise High Performance Computing 15 SP7 SUSE Linux Enterprise Module for Desktop Applications 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Fixed

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-74936 ADVISORY https://vuldb.com/vuln/391589 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:3658/ REF https://bugzilla.mozilla.org/show_bug.cgi?id=2052688 REF https://www.mozilla.org/security/advisories/mfsa2026-74/ REF https://www.mozilla.org/security/advisories/mfsa2026-76/ REF https://www.mozilla.org/security/advisories/mfsa2026-77/ REF https://www.mozilla.org/security/advisories/mfsa2026-78/ REF https://www.mozilla.org/security/advisories/mfsa2026-79/ REF https://www.mozilla.org/security/advisories/mfsa2026-80/

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