Skip to main content

Mozilla Firefox CVE-2026-16377

| EUVDEUVD-2026-46213 CRITICAL
Protection Mechanism Failure (CWE-693)
2026-07-21 mozilla GHSA-9qmg-vj62-g95q
Authentication Bypass Red Hat Mozilla
Critical
Disputed · 9.8 Vendor: mozilla
Share

Severity by source

Sources disagree (Medium–Critical)
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

PDF Viewer flaw requires the victim to open a malicious document, so UI:R; remote/network delivery and no auth (AV:N/PR:N) hold, with high impact reflecting worst-case chaining potential.

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
6.1 MEDIUM
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

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 - 19:38 vuln.today
CVSS changed
Jul 22, 2026 - 18:22 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

Mitigation bypass in the PDF Viewer component. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13.

AnalysisAI

Mitigation bypass in the Mozilla Firefox PDF Viewer component undermines a built-in security control (CWE-693 Protection Mechanism Failure), weakening a defense-in-depth barrier that would otherwise contain malicious PDF content. Mozilla self-reported the issue and shipped fixes in Firefox 153 and Firefox ESR 140.13 via advisories MFSA2026-68 and MFSA2026-70. There is no public exploit identified at time of analysis, and EPSS is very low (0.16%, 6th percentile), so the headline CVSS 9.8 reflects worst-case potential rather than demonstrated mass exploitation.

Technical ContextAI

The affected technology is the PDF Viewer (pdf.js-based) subsystem bundled in Firefox, which renders untrusted PDF documents inside the browser sandbox and relies on layered mitigations to constrain what embedded content can do. CWE-693 (Protection Mechanism Failure) indicates the root cause is not a fresh memory-corruption primitive but the defeat or circumvention of an existing safeguard, meaning a defensive layer that was supposed to block or contain an attack can be bypassed. The single CPE provided, cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*, points to the Firefox application generally; Mozilla's split into a mainline (153) and ESR (140.13) fix confirms both release trains carry the vulnerable component. Because it is a mitigation bypass, its practical danger is greatest when chained with a second bug whose exploitation the bypassed mitigation was designed to prevent.

RemediationAI

Vendor-released patch: upgrade to Firefox 153 (mainline) or Firefox ESR 140.13 (Extended Support Release), whichever channel is deployed, per Mozilla advisories MFSA2026-68 (https://www.mozilla.org/security/advisories/mfsa2026-68/) and MFSA2026-70 (https://www.mozilla.org/security/advisories/mfsa2026-70/). Because the flaw lives in the PDF Viewer, an interim compensating control is to disable Firefox's built-in PDF rendering by setting pdfjs.disabled to true in about:config (or via enterprise policy), which forces PDFs to download instead of rendering in-browser and removes the vulnerable code path; the trade-off is degraded user experience and pushing PDF handling to a separate external viewer that may carry its own risks. Additionally, blocking or scanning untrusted PDF delivery at the email/web gateway reduces the chance a malicious document reaches the viewer, but this is a partial control, not a substitute for the update. Managed environments should push the update through their standard browser update mechanism as the primary and complete fix.

More in Mozilla

View all
CVE-2015-4495 HIGH POC
8.8 Aug 08

The PDF reader in Mozilla Firefox before 39.0.3, Firefox ESR 38.x before 38.1.1, and Firefox OS before 2.2 allows remote
CVE-2013-1690 HIGH POC
8.8 Jun 26

Mozilla Firefox before 22.0, Firefox ESR 17.x before 17.0.7, Thunderbird before 17.0.7, and Thunderbird ESR 17.x before

CVE-2013-0758 CRITICAL POC
9.3 Jan 13

Mozilla Firefox before 18.0, Firefox ESR 10.x before 10.0.12 and 17.x before 17.0.2, Thunderbird before 17.0.2, Thunderb
CVE-2013-0753 CRITICAL POC
9.3 Jan 13

Use-after-free vulnerability in the serializeToStream implementation in the XMLSerializer component in Mozilla Firefox b
CVE-2012-3993 CRITICAL POC
9.3 Oct 10

The Chrome Object Wrapper (COW) implementation in Mozilla Firefox before 16.0, Firefox ESR 10.x before 10.0.8, Thunderbi
CVE-2013-1710 CRITICAL POC
10.0 Aug 07

The crypto.generateCRMFRequest function in Mozilla Firefox before 23.0, Firefox ESR 17.x before 17.0.8, Thunderbird befo
CVE-2017-3823 HIGH POC
8.8 Feb 01

An issue was discovered in the Cisco WebEx Extension before 1.0.7 on Google Chrome, the ActiveTouch General Plugin Conta
CVE-2014-8636 HIGH POC
7.5 Jan 14

The XrayWrapper implementation in Mozilla Firefox before 35.0 and SeaMonkey before 2.32 does not properly interact with

CVE-2013-0757 CRITICAL POC
9.3 Jan 13

The Chrome Object Wrapper (COW) implementation in Mozilla Firefox before 18.0, Firefox ESR 17.x before 17.0.2, Thunderbi
CVE-2014-1510 CRITICAL POC
9.8 Mar 19

The Web IDL implementation in Mozilla Firefox before 28.0, Firefox ESR 24.x before 24.4, Thunderbird before 24.4, and Se
CVE-2014-1511 CRITICAL POC
9.8 Mar 19

Mozilla Firefox before 28.0, Firefox ESR 24.x before 24.4, Thunderbird before 24.4, and SeaMonkey before 2.25 allow remo
CVE-2013-0643 HIGH
8.8 Feb 27

The Firefox sandbox in Adobe Flash Player before 10.3.183.67 and 11.x before 11.6.602.171 on Windows and Mac OS X, and b

Same weakness CWE-693 – Protection Mechanism Failure

View all
CVE-2013-2465 CRITICAL POC
9.8
CVE-2024-21412 HIGH POC
8.1
CVE-2013-0431 MEDIUM POC
5.3
CVE-2019-1003030 CRITICAL POC
9.9
CVE-2025-40536 HIGH POC
8.1
CVE-2024-38217 MEDIUM POC
5.4
CVE-2026-21513 HIGH
8.8
CVE-2026-21510 HIGH POC
8.8

Same technique Authentication Bypass

View all
CVE-2023-22515 CRITICAL POC
9.8
CVE-2012-4681 CRITICAL POC
9.8
CVE-2013-2465 CRITICAL POC
9.8
CVE-2011-3544 CRITICAL POC
9.8
CVE-2022-40684 CRITICAL POC
9.8
CVE-2025-61882 CRITICAL POC
9.8
CVE-2024-0012 CRITICAL POC
9.3
CVE-2023-46805 HIGH POC
8.2

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

Share

CVE-2026-16377 vulnerability details – vuln.today
Back

This site uses cookies essential for authentication and security. No tracking or analytics cookies are used. Privacy Policy