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Mozilla Firefox CVE-2026-74987

| EUVDEUVD-2026-60672 CRITICAL
Buffer Overflow (CWE-119)
2026-08-18 mozilla GHSA-w34f-74jx-hvjc
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 load page
  3. Exploit
    Trigger memory corruption in Gecko engine
  4. Execution
    Corrupt heap/stack memory
  5. Impact
    Execute code in browser process

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

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Exploitation Conditions

Exploitation requires the victim to load attacker-controlled web content in an affected build (Firefox 153, ESR 153.0, or ESR 140.13) - the classic browser drive-by/social-engineering prerequisite. Although the supplied CVSS vector lists UI:N, memory-corruption in a browser engine is triggered by rendering a malicious page, so realistic exploitation depends on user navigation to a hostile or compromised site; there is no authentication requirement (PR:N). Limiting factors: exploitation is probabilistic per Mozilla ('with enough effort some of these could have been exploited'), reliable weaponization of memory-safety bugs is non-trivial, and users on Firefox 154 / ESR 140.14 / ESR 153.1 or later are not affected.
Impact

The provided CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H, base 9.8) rates this as critical, but the UI:N component is questionable: browser memory-corruption bugs realistically require the victim to load malicious web content, i.e., user interaction - verify against Mozilla's own scoring. No EPSS score, KEV entry, POC, or SSVC data was provided, so real-world exploitation signals are absent. Mozilla itself only claims presumed exploitability ('with enough effort some of these could have been exploited'), not demonstrated exploitation, and these are internally-found rather than in-the-wild bugs. Net assessment: a genuine high-priority patch for any browser fleet due to product ubiquity and the code-execution potential, but current evidence points to no active exploitation - prioritize rapid patching over emergency incident response.
Exploit ScenarioDerived

An attacker hosts a malicious web page (or injects malicious content into an ad or compromised site) crafted to trigger the memory-corruption defect in Firefox's rendering engine. When a user running an affected Firefox/ESR version visits the page, the corruption is triggered and, given sufficient exploit engineering, could lead to arbitrary code execution in the browser process. No public exploit is currently known, and Mozilla characterizes exploitability as presumed rather than demonstrated.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.2% exploitation probability (EPSS)

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AnalysisAIv1 – Aug 19, 2026

Memory corruption in Mozilla Firefox 153, Firefox ESR 153.0, and Firefox ESR 140.13 allows remote attackers to potentially execute arbitrary code within the browser process when a victim renders attacker-controlled web content. Mozilla internally discovered a batch of memory-safety defects (tracked across advisories MFSA2026-74 through MFSA2026-80) and states that some showed evidence of memory corruption presumed exploitable with sufficient effort. No public exploit identified at time of analysis, and the issue is not listed in CISA KEV; it is fixed in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1.

RemediationAI

Vendor-released patch: upgrade to Firefox 154, Firefox ESR 140.14, or Firefox ESR 153.1 depending on your channel - this is the primary and complete fix. Standard release users should move to 154; enterprises on the ESR channel should apply 140.14 (140.x line) or 153.1 (153.x line). Consult the Mozilla advisories at https://www.mozilla.org/security/advisories/mfsa2026-74/ (and MFSA2026-76 through -80) for per-bug detail. As an interim compensating control until patching, deploy a strict content policy - enable Firefox's built-in defenses and consider disabling JavaScript for untrusted sites (via NoScript or policy), which sharply reduces the attack surface for engine memory-corruption but breaks most modern web applications; restricting browsing to trusted internal sites via proxy allow-listing is a lower-impact alternative for locked-down environments.

Affects your stack

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Technical ContextAI · show details

This is a rollup of internally-found memory-safety bugs in Firefox's rendering/JavaScript engine (Gecko/SpiderMonkey), classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), consistent with the 'Buffer Overflow' tag. The affected CPE is cpe:2.3:a:mozilla:firefox covering the browser application. Bugs of this class typically stem from unsafe memory operations in C/C++ components handling untrusted input (HTML/CSS/JS parsing, image/media decoding, layout), where out-of-bounds reads or writes can corrupt heap or stack memory. Mozilla aggregates such internally-discovered defects into single advisories with cross-referenced Bugzilla IDs (e.g., bug 2059424 and the buglist references), a long-standing practice for its 'memory safety bugs' series.

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  • Exploit and PoC references, threat intelligence from 22 sources
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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 7.5 HIGH

Browser memory-corruption needs the victim to load malicious content (UI:R) and reliable exploitation of memory-safety bugs is non-trivial (AC:H); no auth (PR:N) and full code-execution impact (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:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
SUSE HIGH
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

3
CVSS changed
Aug 19, 2026 - 13:22 NVD
9.8 (CRITICAL)
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 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 140.14, and Firefox ESR 153.1.

Executive ViewAI

Why It Matters

A critical memory corruption vulnerability in Mozilla Firefox (versions 153, ESR 140.13, 153.0) enables arbitrary code execution when users view attacker-controlled web content, potentially compromising any employee or customer with these browsers. This directly threatens data confidentiality and system integrity across the organization. No active exploitation has been reported, but remediation is critical given the severity.

Business Impact: Severe
Compensating Controls

Apply vendor patch.

Threat Intelligence Overview

EPSS Score
0.2%
Top 92% exploitable
Prevalence
High
Major cross-platform web browser with hundreds of millions of users worldwide
Data Quality
6 sources
Confidence: High
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

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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Same weakness CWE-119 – Buffer Overflow

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10.0
CVE-2017-11882 HIGH POC
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CVE-2015-2426 HIGH POC
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CVE-2013-3918 HIGH POC
8.8
CVE-2023-4966 HIGH POC
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CVE-2017-11774 HIGH POC
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CVE-2013-3660 HIGH POC
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Same technique Buffer Overflow

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CVE-2011-2462 CRITICAL POC
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CVE-2019-11043 CRITICAL POC
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CVE-2009-0927 HIGH POC
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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-2026-74987 ADVISORY https://vuldb.com/vuln/391621 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:3658/ REF https://bugzilla.mozilla.org/buglist.cgi?bug_id=1500946%2C1788109%2C2045379%2C2045380%2C2049339%2C2049393%2C2053580%2C2054662%2C2054665%2C2054673%2C2054785%2C2058645 REF https://bugzilla.mozilla.org/buglist.cgi?bug_id=2048797%2C2050536%2C2053272%2C2053579%2C2057115%2C2057116%2C2057130%2C2057991%2C2057995%2C2058002%2C2058008%2C2058032%2C2058102%2C2058667 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2059424 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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