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Mozilla Firefox CVE-2026-16351

| EUVDEUVD-2026-46192 CRITICAL
Use After Free (CWE-416)
2026-07-21 mozilla GHSA-frvf-6637-jq2q
Information Disclosure Use After Free 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
8.3 HIGH

Reachable from web content but requires the user to visit a malicious page (UI:R) and reliable UAF grooming plus sandbox escape (AC:H); crossing the sandbox boundary is a scope change (S:C).

3.1 AV:N/AC:H/PR:N/UI:R/S:C/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:H/SI:H/SA:H
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 - 17:16 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

Sandbox escape due to use-after-free in the DOM: Navigation component. This vulnerability was fixed in Firefox 153, Firefox ESR 115.38, and Firefox ESR 140.13.

AnalysisAI

Sandbox escape in Mozilla Firefox stems from a use-after-free (CWE-416) in the DOM: Navigation component, letting web-reachable content corrupt memory and cross the content-process sandbox boundary. Affected builds are Firefox before 153, Firefox ESR before 115.38, and Firefox ESR before 140.13; Mozilla self-reported the issue and shipped fixes across all three branches (MFSA-2026-68/69/70). There is no public exploit identified at time of analysis, and EPSS is low (0.15%, 5th percentile), indicating no observed weaponization yet despite the 9.8 CVSS rating.

Technical ContextAI

The flaw lives in Firefox's DOM Navigation subsystem, the engine code that manages page/document loading, history traversal, and session transitions inside the Gecko content process. A use-after-free (CWE-416) occurs when a Navigation-related object is freed while a reference to it is still live, allowing later reads/writes to reclaimed heap memory. Because navigation objects are directly driven by attacker-controllable web content (links, redirects, history APIs), the freed-then-reused allocation can be groomed to achieve controlled memory corruption. Per the CPE (cpe:2.3:a:mozilla:firefox), all Firefox variants sharing this Gecko code are in scope. The 'sandbox escape' classification signals the primitive is powerful enough to break out of the renderer sandbox rather than merely crash the tab, which is why Mozilla tags it as both Memory Corruption and Information Disclosure.

RemediationAI

Vendor-released patch: upgrade to Firefox 153, Firefox ESR 115.38, or Firefox ESR 140.13 as appropriate for your channel - this is the definitive fix and should be the primary action, referencing MFSA-2026-68/69/70 for your deployed branch. Enterprises on the ESR channel should note two ESR trains are patched (115.38 and 140.13), so confirm which line your fleet runs before staging updates. No standalone workaround is published; because the bug is reachable through ordinary DOM navigation there is no single feature toggle that reliably neutralizes it, so compensating controls are limited to reducing exposure: restrict browsing to trusted sites via web proxy/URL filtering and enforce automatic browser updates through enterprise policy (Firefox policies.json/GPO) to shrink the exposure window. These controls reduce but do not eliminate risk and can disrupt legitimate browsing, so they are stopgaps only until the patched build is deployed.

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Same weakness CWE-416 – Use After Free

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Same technique Information Disclosure

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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-2026-16351 vulnerability details – vuln.today
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