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Mozilla Firefox CVE-2026-16363

| EUVDEUVD-2026-46194 CRITICAL
Incorrect Calculation (CWE-682)
2026-07-21 mozilla GHSA-3mwp-7c29-vp5v
Information Disclosure 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
7.5 HIGH

Remote via malicious page but victim must load content (UI:R) and reliable JIT exploitation is non-trivial (AC:H); no auth needed (PR:N) and memory corruption yields high CIA in the content process.

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
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 - 17:12 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: WebAssembly component. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13.

AnalysisAI

Memory-safety corruption in Mozilla Firefox stems from a JIT miscompilation in the JavaScript engine's WebAssembly component, fixed in Firefox 153 and Firefox ESR 140.13. An attacker who lures a victim to a malicious page can supply crafted WebAssembly that the Just-In-Time compiler translates incorrectly, corrupting engine state to disclose memory or achieve code execution in the content process. There is no public exploit identified at time of analysis and the EPSS score is very low (0.15%, 5th percentile), so no active exploitation is indicated despite the 9.8 rating.

Technical ContextAI

The flaw lives in SpiderMonkey, Firefox's JavaScript engine, specifically the WebAssembly (Wasm) execution path that is optimized through a Just-In-Time (JIT) compiler. CWE-682 (Incorrect Calculation) describes the root cause: the JIT emits machine code whose computed values, bounds, or type assumptions diverge from the semantics the source Wasm actually requires, so an operation produces a wrong result or skips a required check. In a JIT this class of bug typically manifests as out-of-bounds reads/writes or type confusion because the compiler's incorrect assumptions eliminate safety guards, giving attacker-controlled script primitives over process memory. The CPE cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* scopes impact to the Firefox application, and the ESR advisory shows Firefox ESR 140.x shares the same affected code path.

RemediationAI

Vendor-released patch: Firefox 153 and Firefox ESR 140.13 - upgrade to these or later builds, which is the primary and complete fix per Mozilla advisories MFSA2026-68 and MFSA2026-70. Because Firefox auto-updates by default, ensure automatic updates are enabled and restart the browser to apply; in managed enterprise fleets push the updated package through your software distribution channel and confirm the reported version. As an interim compensating control until patching, WebAssembly can be disabled by setting javascript.options.wasm to false in about:config (or via enterprise policy), which removes the vulnerable code path at the cost of breaking sites and applications that rely on Wasm; disabling JavaScript entirely is more disruptive and generally not warranted for this issue. Reference advisories: https://www.mozilla.org/security/advisories/mfsa2026-68/ and https://www.mozilla.org/security/advisories/mfsa2026-70/.

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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-2026-16363 vulnerability details – vuln.today
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