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Mozilla Firefox CVE-2026-74990

| EUVDEUVD-2026-60673 CRITICAL
Buffer Overflow (CWE-119)
2026-08-18 mozilla GHSA-x3gf-4r72-x3gv
Buffer Overflow Mozilla
9.8
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
    Lure victim to render content
  3. Exploit
    Trigger memory corruption in Firefox
  4. Execution
    Corrupt heap / control flow
  5. Impact
    Potential arbitrary code execution in browser

Vulnerability Assessment

Weakness
CWE
CWE-119
ASVS 5.0
V15 - Secure Coding and Architecture Bounds checking, buffer size validation
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 a vulnerable Firefox or ESR build (153/ESR 115.38/140.13/153.0 or earlier); despite the CVSS UI:N marking, browser memory-corruption of this class in practice needs the user to visit or render a malicious page, so user interaction is effectively a prerequisite and a limiting factor. No authentication or elevated privileges are needed on the target (PR:N), and no non-default configuration is required - a default Firefox install is affected. The primary limiters are the required page-render/user-visit step and the fact that Mozilla only presumes exploitability, so a working exploit likely demands significant attacker effort against browser hardening (sandboxing, ASLR).
Impact

The headline CVSS is 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), which reflects NVD's worst-case scoring for a network-reachable memory-corruption bug, but for a browser this is almost certainly overstated on user interaction: exploitation realistically requires the victim to visit or render malicious web content, i.e. UI:R, which lowers the practical base score to roughly 8.8. Mozilla's own language is deliberately hedged ('presume that with enough effort some of these could have been exploited'), meaning exploitability is inferred, not demonstrated. There is no CISA KEV listing, no EPSS score provided, and no public proof-of-concept in the supplied data, so this is a high-severity-but-not-confirmed-exploited case rather than an emergency; even so, browsers are a top drive-by attack surface and any organization running affected builds should patch promptly on normal-but-expedited timelines. The main uncertainty is the UI:N vs. UI:R discrepancy and the absence of exploitation telemetry - these should be verified against the individual MFSA advisories before treating raw 9.8 as ground truth.
Exploit ScenarioDerived

An attacker hosts or compromises a web page containing content crafted to trigger one of the memory-corruption bugs, then lures a victim running an affected Firefox/ESR build to visit it (e.g., via phishing link or a malvertising redirect). Rendering the page corrupts browser heap memory, which a skilled attacker could potentially leverage toward arbitrary code execution in the browser process. No public exploit is identified at time of analysis, and Mozilla only assesses exploitation as plausible rather than proven.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.6% exploitation probability (EPSS)

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AnalysisAIv1 – Aug 18, 2026

Memory-corruption defects in Mozilla Firefox and its ESR channels allow potential arbitrary code execution when a user renders attacker-controlled web content, per Mozilla advisories MFSA2026-74 through MFSA2026-80. The flaws were found internally by Mozilla across Firefox 153 and ESR 115.38/140.13/153.0, and Mozilla states some showed evidence of memory corruption that could plausibly be exploited. No public exploit identified at time of analysis; the issues are already fixed in Firefox 154, ESR 115.39, 140.14, and 153.1.

RemediationAI

Vendor-released patch: upgrade to Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, or Firefox ESR 153.1 depending on your channel - this is the definitive fix. Enterprises on the ESR track should map their current build (115.x, 140.x, or 153.x) to the matching fixed ESR release rather than jumping channels. Consult the relevant Mozilla advisories (MFSA2026-74 through MFSA2026-80) to confirm which specific issues apply to your deployment. Until updates are rolled out, compensating controls include enforcing automatic browser updates via enterprise policy, and reducing drive-by exposure by restricting untrusted web browsing or enabling stricter content controls; note these are partial mitigations only, since any rendered malicious content is a potential trigger and there is no configuration toggle that disables the vulnerable code paths.

Affects your stack

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Technical ContextAI · show details

This is a bundled browser memory-safety advisory (CWE-119: improper restriction of operations within the bounds of a memory buffer, tagged 'Buffer Overflow'). Firefox is built largely in C++ (with Rust components), and CWE-119-class bugs in the layout, JavaScript (SpiderMonkey), graphics, or media-parsing engines can let malformed web content trigger out-of-bounds reads/writes or use-after-free-like corruption of heap memory. The affected component per CPE is cpe:2.3:a:mozilla:firefox (all versions up to the fixed builds), covering both the rapid-release channel (153) and the Extended Support Release channels (115.x, 140.x, 153.x) that enterprises typically deploy. As is standard for Mozilla, the CVE aggregates dozens of individually tracked Bugzilla issues (bug IDs 2045762-2059188) rather than a single defect.

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Severity by source

Vendor (mozilla) 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 no privileges (AV:N/PR:N), but requires the victim to render a malicious page, so UI:R rather than UI:N; memory corruption plausibly yields full CIA impact.

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 Vendor (mozilla).

CVSS VectorVendor: mozilla

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

Lifecycle Timeline

2
CVE Published
Aug 18, 2026 - 12:23 cve.org
UNKNOWN (no severity yet)
CVE Published
Aug 18, 2026 - 12:23 cve.org
CRITICAL 9.8

DescriptionCVE.org

Internally found bugs present in Firefox ESR 115.38, Firefox ESR 140.13, Firefox ESR 153.0 and Firefox 153. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, and Firefox ESR 153.1.

Articles & Coverage 1

News Critical Memory Corruption RCE in Mozilla Firefox - CVE-2026-74990 Aug 19, 2026

Executive ViewAI

Why It Matters

Mozilla Firefox and ESR channels contain critical memory-corruption vulnerabilities (CVE-2026-74990, CVSS 9.8) that enable arbitrary code execution when users visit attacker-controlled websites. Any Firefox user in the organization can be compromised without requiring authentication or specialized user interaction, posing an immediate threat to endpoint security and data confidentiality.

Business Impact: Severe
Compensating Controls

Vendor-released patch: Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, Firefox ESR 153.1. Until deployment: restrict Firefox use to non-sensitive browsing or require isolated sandboxed browsers for high-risk internet activity.

Threat Intelligence Overview

EPSS Score
0.6%
Top 56% exploitable
Prevalence
High
major desktop browser with large enterprise ESR footprint 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 CRITICAL
CISA KEV No
Public POC No
EPSS 0.6%
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
Out-of-Cycle
Exploitation
None
System Exposure· derived
Open
Automatable
Yes
Human Impact
Very High
Technical Impact
Total

Priority Score

50
Low Medium High Critical
KEV: 0
EPSS: +1
CVSS: +49
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Affected Products (CPE)CVE.org

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

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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-119 – Buffer Overflow

View all
CVE-2020-0796 CRITICAL POC
10.0
CVE-2017-11882 HIGH POC
7.8
CVE-2014-6332 HIGH POC
8.8
CVE-2015-2426 HIGH POC
8.8
CVE-2013-3918 HIGH POC
8.8
CVE-2023-4966 HIGH POC
7.5
CVE-2017-11774 HIGH POC
7.8
CVE-2013-3660 HIGH POC
7.8

Same technique Buffer Overflow

View all
CVE-2017-7269 CRITICAL POC
9.8
CVE-2015-5119 CRITICAL POC
9.8
CVE-2015-3113 CRITICAL POC
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CVE-2011-2462 CRITICAL POC
9.8
CVE-2019-11043 CRITICAL POC
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CVE-2009-0927 HIGH POC
8.8
CVE-2012-1889 HIGH POC
8.8

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-2026-74990 ADVISORY https://vuldb.com/vuln/391641 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:3658/ REF https://bugzilla.mozilla.org/buglist.cgi?bug_id=2045762%2C2052401%2C2058208 REF https://bugzilla.mozilla.org/buglist.cgi?bug_id=2045774%2C2048490%2C2050864%2C2053159%2C2053260%2C2053261%2C2053582%2C2053599%2C2053607%2C2053608%2C2053853%2C2054626%2C2054627%2C2054635%2C2054677%2C2054740%2C2054832%2C2056792%2C2057098%2C2057100%2C2057101%2C2057103%2C2057117%2C2057118%2C2058048%2C2058049%2C2058622%2C2058623%2C2058665%2C2058666%2C2059121%2C2059164%2C2059188 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/

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