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Mozilla Firefox CVE-2026-12299

| EUVDEUVD-2026-37090 MEDIUM
Access of Resource Using Incompatible Type (Type Confusion) (CWE-843)
2026-06-16 mozilla GHSA-4885-5pch-3x6m
Mozilla Memory Corruption Information Disclosure
Medium
Disputed · 5.4 Vendor: mozilla
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Severity by source

Sources disagree (Medium–Critical)
Vendor (mozilla) PRIMARY
5.4 MEDIUM
AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
vuln.today AI
5.4 MEDIUM

Network-delivered browser exploit requires active user page visit (UI:R); type confusion yields limited memory read/write (C:L/I:L) without scope change or availability impact.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
SUSE
CRITICAL
qualitative
Red Hat
7.5 HIGH
qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorVendor: mozilla

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

Lifecycle Timeline

3
Analysis Generated
Jun 16, 2026 - 15:52 vuln.today
CVSS changed
Jun 16, 2026 - 15:22 NVD
5.4 (MEDIUM)
CVE Published
Jun 16, 2026 - 11:52 cve.org
UNKNOWN (no severity yet)

DescriptionCVE.org

JIT miscompilation in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, and Firefox ESR 115.37.

AnalysisAI

JIT miscompilation in Mozilla Firefox's DOM Core & HTML component enables memory corruption and limited information disclosure when a user visits a malicious web page. Affecting Firefox prior to 152, Firefox ESR 140.x prior to 140.12, and Firefox ESR 115.x prior to 115.37, the root cause is a type confusion (CWE-843) in the Just-In-Time compiler that mishandles type information during DOM object operations. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Craft malicious JavaScript targeting DOM JIT miscompilation
Delivery
Deliver page URL via phishing or malvertising
Exploit
User loads page in vulnerable Firefox
Execution
JIT compiler miscompiles DOM type operation
Persist
Type confusion reads or corrupts browser memory
Impact
Limited data disclosure or integrity impact within browser process
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Vulnerability AssessmentAI

Exploitation Exploitation requires a user to actively visit or load attacker-controlled web content in a vulnerable version of Firefox, triggering JIT compilation of crafted JavaScript targeting DOM Core or HTML operations. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 3.1 score of 5.4 Medium with vector AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N reflects a network-reachable flaw requiring no authentication but mandating user interaction, with limited and contained impact (no availability impact, no scope change). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker hosts a malicious web page containing crafted JavaScript designed to trigger the JIT compiler's type confusion when processing DOM Core or HTML objects. When an unpatched Firefox user visits the page - delivered via phishing link, malvertising, or a compromised legitimate site - the JIT compiler miscompiles the DOM operation, producing native code that accesses memory using an incompatible type, potentially leaking limited browser memory contents or corrupting internal browser state. …
Remediation Upgrade to Firefox 152 or later for standard release users. … Detailed patch versions, workarounds, and compensating controls in full report.
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Same weakness CWE-843 – Access of Resource Using Incompatible Type (Type Confusion)

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Same technique Memory Corruption

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Vendor StatusVendor

SUSE

Severity: Critical
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected

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CVE-2026-12299 vulnerability details – vuln.today
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