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Mozilla Firefox CVE-2026-16355

| EUVDEUVD-2026-46203 CRITICAL
Access of Resource Using Incompatible Type (Type Confusion) (CWE-843)
2026-07-21 mozilla GHSA-vcc7-rj3q-v3r3
Information Disclosure Memory Corruption Red Hat Mozilla
9.8
CVSS 3.1 · Vendor: mozilla
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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 low complexity and no privileges, but realistically requires the victim to visit a malicious page, so UI:R; memory corruption yields high C/I/A.

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
CRITICAL
qualitative
Red Hat
7.5 HIGH
qualitative

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

4
Analysis Generated
Jul 22, 2026 - 17:13 vuln.today
CVSS changed
Jul 22, 2026 - 16:22 NVD
9.8 (CRITICAL)
CVE Published
Jul 21, 2026 - 12:37 cve.org
UNKNOWN (no severity yet)
CVE Published
Jul 21, 2026 - 12:37 cve.org
CRITICAL 9.8

DescriptionCVE.org

JIT miscompilation in the JavaScript Engine: JIT component. This vulnerability was fixed in Firefox 153, Firefox ESR 115.38, and Firefox ESR 140.13.

AnalysisAI

Memory corruption in Mozilla Firefox's JavaScript engine JIT compiler allows attackers to corrupt memory and potentially achieve arbitrary code execution when a victim visits a malicious web page. The flaw stems from a JIT miscompilation (type confusion, CWE-843) affecting Firefox before 153, ESR before 115.38, and ESR before 140.13, and carries CVSS 9.8. There is no public exploit identified at time of analysis and EPSS exploitation probability is low (0.15%, 5th percentile).

Technical ContextAI

The vulnerability lives in Firefox's SpiderMonkey JavaScript engine, specifically its Just-In-Time (JIT) compiler that converts hot JavaScript into optimized native machine code. A miscompilation causes the JIT to generate code that operates on a value under an incorrect type assumption - the classic CWE-843 (Type Confusion) root cause. When the optimizer's speculated type diverges from an object's actual runtime type, the generated native code reads or writes memory using the wrong object layout, producing controllable memory corruption. Because the affected component is the JS engine reachable by any script on any rendered page, the attack surface is the browser content process. The single affected CPE is cpe:2.3:a:mozilla:firefox, and Mozilla tags this as Memory Corruption and Information Disclosure.

RemediationAI

Vendor-released patch: upgrade to Firefox 153, Firefox ESR 115.38, or Firefox ESR 140.13 depending on the release channel in use, as documented in Mozilla advisories MFSA2026-68/69/70 (https://www.mozilla.org/security/advisories/mfsa2026-68/, https://www.mozilla.org/security/advisories/mfsa2026-69/, https://www.mozilla.org/security/advisories/mfsa2026-70/). For managed fleets, push the update via enterprise policy or the built-in updater immediately. As an interim compensating control, disabling the JIT via about:config (setting javascript.options.baselinejit, javascript.options.ion, and related preferences to false, deployable through enterprise policy) removes the vulnerable compilation path at a significant JavaScript performance cost; alternatively, restricting browsing to trusted sites or blocking untrusted script execution reduces exposure but degrades usability. These mitigations are stopgaps only - apply the patched version to fully resolve the issue.

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Same weakness CWE-843 – Access of Resource Using Incompatible Type (Type Confusion)

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Vendor StatusVendor

SUSE

Severity: Critical
Product Status
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
SUSE Linux Enterprise Module for Desktop Applications 15 SP7 Affected

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CVE-2026-16355 vulnerability details – vuln.today
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