Skip to main content

Mozilla Firefox CVE-2026-74940

| EUVDEUVD-2026-60747 CRITICAL
Use After Free (CWE-416)
2026-08-18 mozilla GHSA-x9jf-q439-hfmv
Information Disclosure Use After Free Memory Corruption Red Hat Mozilla Suse
9.8
CVSS 3.1 · NVD
View

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 text/font content
  3. Exploit
    Trigger use-after-free in Graphics: Text
  4. Execution
    Groom heap to control freed object
  5. Impact
    Achieve code execution or info leak 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.

Sign in to read
Exploitation Conditions

Exploitation requires the victim to render attacker-controlled web content in an unpatched Firefox build - the trigger is in the Graphics: Text rendering path, so the attacker must get malicious text/font content loaded and displayed (a visited web page, iframe, or ad). No authentication is required (CVSS PR:N). The primary limiting factor is that, despite the CVSS UI:N marking, a browser rendering bug in practice depends on the user loading the malicious content, and reliable exploitation of a use-after-free typically also requires successful heap grooming and, on modern Firefox, a bypass of sandboxing/ASLR mitigations. Systems already updated to Firefox 154, ESR 115.39, ESR 140.14, or ESR 153.1 are not exploitable.
Impact

The signals are mixed. The published CVSS 3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/C:H/I:H/A:H) implies trivial unauthenticated remote code execution against defaults, but this rating is questionable for a browser rendering bug: exploitation realistically requires a user to load attacker-controlled content, so UI:N understates the true precondition and the effective severity is closer to High-via-UI:R than a wormable 9.8 - verify against Mozilla's own advisory rating. Counterbalancing the high CVSS, EPSS is only 0.16% (6th percentile), there is no CISA KEV listing and no known public POC, so this is not evidence of active or imminent mass exploitation. That said, Firefox's very large install base and the historical reliability of graphics/text UAFs as exploitation targets mean any organization running Firefox - from large enterprises down to a mid-sized municipal IT team maintaining a standard desktop fleet - should treat prompt patching as routine urgent hygiene rather than optional. Net assessment: genuinely worth prioritizing for patch deployment due to product prevalence and impact potential, but not a drop-everything emergency absent evidence of exploitation.
Exploit ScenarioDerived

An attacker hosts or compromises a web page containing crafted text/font content that triggers the use-after-free when Firefox renders it; the victim simply visits the page (or loads it via a malicious ad or iframe). Successful heap grooming lets the attacker corrupt memory to leak sensitive process data or achieve code execution in the content process. No public exploit is currently identified, so this scenario is theoretical based on the vulnerability class.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.2% exploitation probability (EPSS)

Get an e-mail when this CVE is exploited, patched or re-scored. Free account.

Alert me

AnalysisAIv1 – Aug 20, 2026

Memory corruption in Mozilla Firefox's Graphics: Text component (CWE-416 use-after-free) can be triggered by malicious web content, potentially leading to remote code execution or information disclosure in the browser process. All Firefox users on pre-fix builds are affected until updated to Firefox 154 or the corresponding ESR releases (115.39, 140.14, 153.1). There is no public exploit identified at time of analysis, and EPSS exploitation probability is low (0.16%, 6th percentile).

RemediationAI

Vendor-released patch: upgrade to Firefox 154, or to the matching ESR line - Firefox ESR 115.39, ESR 140.14, or ESR 153.1 depending on which ESR branch is deployed. This is the definitive fix; there is no supported configuration workaround for a memory-safety bug in the rendering engine. As interim compensating controls before patching, you can reduce attack surface by disabling JavaScript for untrusted sites (which breaks most modern web applications and is disruptive) or by enforcing strict browsing to trusted sites via web proxy/URL filtering, but neither fully eliminates the risk since the bug is in text/graphics rendering that can be reached by ordinary page content. Enterprises should push the update via their managed-update mechanism (Firefox auto-update, ESR policy, or endpoint management) and confirm the running build post-deployment. Reference the corresponding advisory (https://www.mozilla.org/security/advisories/mfsa2026-74/) for the exact channel affected.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Sign in to check
Technical ContextAI · show details

The flaw is a use-after-free (CWE-416) in Firefox's text-rendering path within the Graphics: Text subsystem, which handles glyph shaping, font layout, and text painting. Use-after-free occurs when the browser frees a heap object but a dangling pointer is later dereferenced, allowing an attacker who controls page content (fonts, DOM text nodes, CSS-driven reflow) to influence the freed memory and corrupt the heap. The CPE cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* confirms the affected product is the Firefox application across versions prior to the fix. Such graphics/text UAFs in browsers are a classic memory-safety class typically exploited by grooming the heap so the reclaimed allocation contains attacker-chosen data.

Know when Mozilla gets its next vulnerability

  • Watch products and get an email when something new is published
  • Check this CVE against your own stack and servers
  • Exploit and PoC references, threat intelligence from 22 sources
Continue with Google Continue with GitHub

No credit card · 7-day full trial

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 7.5 HIGH

Reachable remotely via web content but requires the victim to load a page (UI:R) and reliable use-after-free exploitation needs heap grooming (AC:H); no auth needed and full memory-corruption impact gives C/I/A:H.

3.1 AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
4.0 AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
SUSE HIGH
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 - 20:37 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 Graphics: Text component. This vulnerability was fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, and Firefox ESR 153.1.

Executive ViewAI

Why It Matters

Mozilla Firefox users face critical remote code execution risk through a use-after-free vulnerability in the Graphics text component triggered by malicious web content during normal browsing. No public exploit identified at time of analysis, but the CVSS 9.8 severity and network-accessible attack vector create organization-wide exposure for any workforce using Firefox. Organizations must prioritize immediate patching to eliminate this high-impact attack surface before threat actors develop reliable exploits.

Business Impact: Severe
Compensating Controls

Apply vendor patch.

Threat Intelligence Overview

EPSS Score
0.2%
Top 94% exploitable
Prevalence
High
one of the most widely deployed desktop web browsers worldwide
Data Quality
4 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
Out-of-Cycle
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact
Very 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:*:*:*:*:*:*:*:*

More in Mozilla

View all
CVE-2015-4495 HIGH POC
8.8 Aug 08

The PDF reader in Mozilla Firefox before 39.0.3, Firefox ESR 38.x before 38.1.1, and Firefox OS before 2.2 allows remote
CVE-2013-1690 HIGH POC
8.8 Jun 26

Mozilla Firefox before 22.0, Firefox ESR 17.x before 17.0.7, Thunderbird before 17.0.7, and Thunderbird ESR 17.x before

CVE-2013-0758 CRITICAL POC
9.3 Jan 13

Mozilla Firefox before 18.0, Firefox ESR 10.x before 10.0.12 and 17.x before 17.0.2, Thunderbird before 17.0.2, Thunderb
CVE-2013-0753 CRITICAL POC
9.3 Jan 13

Use-after-free vulnerability in the serializeToStream implementation in the XMLSerializer component in Mozilla Firefox b
CVE-2012-3993 CRITICAL POC
9.3 Oct 10

The Chrome Object Wrapper (COW) implementation in Mozilla Firefox before 16.0, Firefox ESR 10.x before 10.0.8, Thunderbi
CVE-2013-1710 CRITICAL POC
10.0 Aug 07

The crypto.generateCRMFRequest function in Mozilla Firefox before 23.0, Firefox ESR 17.x before 17.0.8, Thunderbird befo
CVE-2017-3823 HIGH POC
8.8 Feb 01

An issue was discovered in the Cisco WebEx Extension before 1.0.7 on Google Chrome, the ActiveTouch General Plugin Conta
CVE-2014-8636 HIGH POC
7.5 Jan 14

The XrayWrapper implementation in Mozilla Firefox before 35.0 and SeaMonkey before 2.32 does not properly interact with

CVE-2013-0757 CRITICAL POC
9.3 Jan 13

The Chrome Object Wrapper (COW) implementation in Mozilla Firefox before 18.0, Firefox ESR 17.x before 17.0.2, Thunderbi
CVE-2014-1510 CRITICAL POC
9.8 Mar 19

The Web IDL implementation in Mozilla Firefox before 28.0, Firefox ESR 24.x before 24.4, Thunderbird before 24.4, and Se
CVE-2014-1511 CRITICAL POC
9.8 Mar 19

Mozilla Firefox before 28.0, Firefox ESR 24.x before 24.4, Thunderbird before 24.4, and SeaMonkey before 2.25 allow remo
CVE-2013-0643 HIGH
8.8 Feb 27

The Firefox sandbox in Adobe Flash Player before 10.3.183.67 and 11.x before 11.6.602.171 on Windows and Mac OS X, and b

Same weakness CWE-416 – Use After Free

View all
CVE-2019-0708 CRITICAL POC
9.8
CVE-2015-5119 CRITICAL POC
9.8
CVE-2014-0322 HIGH POC
8.8
CVE-2012-4792 HIGH POC
8.8
CVE-2009-4324 HIGH POC
7.8
CVE-2015-0313 CRITICAL POC
9.8
CVE-2015-5122 CRITICAL POC
9.8
CVE-2013-2551 HIGH POC
8.8

Same technique Information Disclosure

View all
CVE-2019-2725 CRITICAL POC
9.8
CVE-2021-34523 CRITICAL POC
9.0
CVE-2013-2251 CRITICAL POC
9.8
CVE-2017-5638 CRITICAL POC
9.8
CVE-2025-24813 CRITICAL POC
9.8
CVE-2025-68613 HIGH POC
8.8
CVE-2015-1701 HIGH POC
7.8
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-2026-74940 ADVISORY https://vuldb.com/vuln/391592 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:3658/ REF https://bugzilla.mozilla.org/show_bug.cgi?id=2054842 REF https://www.mozilla.org/security/advisories/mfsa2026-74/ REF https://www.mozilla.org/security/advisories/mfsa2026-75/ 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/

Search Externally

GitHub PoC Exploit-DB PacketStorm Snyk Rapid7 Nuclei Templates Trickest PoC
Back

This site uses cookies essential for authentication and security. No tracking or analytics cookies are used. Privacy Policy