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Firefox Esr CVE-2026-4700

| EUVDEUVD-2026-14817 CRITICAL
Authentication Bypass Using an Alternate Path or Channel (CWE-288)
2026-03-24 mozilla GHSA-4pf4-jp4v-4g5c
9.8
CVSS 3.1 · NVD
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Severity by source

NVD PRIMARY
9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
SUSE
CRITICAL
qualitative
Red Hat
7.5 HIGH
qualitative

Primary rating from NVD.

CVSS VectorNVD

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

Lifecycle Timeline

4
Patch released
Mar 31, 2026 - 21:13 nvd
Patch available
EUVD ID Assigned
Mar 24, 2026 - 12:45 euvd
EUVD-2026-14817
Analysis Generated
Mar 24, 2026 - 12:45 vuln.today
CVE Published
Mar 24, 2026 - 12:30 nvd
CRITICAL 9.8

DescriptionNVD

Mitigation bypass in the Networking: HTTP component. This vulnerability affects Firefox < 149 and Firefox ESR < 140.9.

AnalysisAI

This vulnerability is a mitigation bypass in Firefox's HTTP networking component that allows attackers to circumvent existing security controls. Firefox versions below 149 and Firefox ESR versions below 140.9 are affected, enabling attackers to bypass authentication or other HTTP-level protections. While specific CVSS and EPSS scores are not provided, the mitigation bypass classification and Mozilla's issuance of security advisories indicate this requires prompt patching.

Technical ContextAI

The vulnerability exists in the HTTP networking stack of Mozilla Firefox (cpe:2.3:a:mozilla:firefox) and Firefox ESR (cpe:2.3:a:mozilla:firefox_esr), which handle HTTP protocol operations and related security mitigations. The root cause is classified as an authentication bypass, suggesting that security controls intended to protect HTTP transactions—such as header validation, certificate pinning, or other protocol-level protections—can be circumvented by a malicious actor. The issue was tracked internally by Mozilla in Bugzilla (bug 2003766) and addressed across two security advisories (MFSA 2026-20 and MFSA 2026-22), indicating it may affect multiple code paths or have been resolved in phases.

RemediationAI

Immediately upgrade Firefox to version 149 or later and Firefox ESR to version 140.9 or later via the built-in auto-update mechanism or manual download from https://www.mozilla.org/. For organizations that cannot immediately patch, implement network-level controls such as enforcing HTTPS with HSTS headers, deploying a web application firewall to detect suspicious HTTP patterns, and restricting outbound Firefox connections to trusted, verified endpoints. Monitor for any suspicious authentication bypass attempts in logs and consider disabling HTTP (non-HTTPS) traffic where feasible during the interim patching period.

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Vendor StatusVendor

Debian

firefox
Release Status Fixed Version Urgency
sid vulnerable 148.0.2-1 -
(unstable) fixed (unfixed) -
firefox-esr
Release Status Fixed Version Urgency
bullseye vulnerable 115.14.0esr-1~deb11u1 -
bullseye (security) vulnerable 140.8.0esr-1~deb11u1 -
bookworm vulnerable 128.14.0esr-1~deb12u1 -
bookworm (security) vulnerable 140.8.0esr-1~deb12u1 -
trixie (security), trixie vulnerable 140.8.0esr-1~deb13u1 -
forky, sid vulnerable 140.8.0esr-1 -
(unstable) fixed (unfixed) -

SUSE

Severity: Critical
Product Status
Image SLES15-SP5-SAP-Azure-LI-BYOS Image SLES15-SP5-SAP-Azure-LI-BYOS-Production Image SLES15-SP5-SAP-Azure-VLI-BYOS Image SLES15-SP5-SAP-Azure-VLI-BYOS-Production Image SLES15-SP6-SAP-Azure-LI-BYOS Image SLES15-SP6-SAP-Azure-LI-BYOS-Production Image SLES15-SP6-SAP-Azure-VLI-BYOS Image SLES15-SP6-SAP-Azure-VLI-BYOS-Production Image SLES15-SP7-SAP-Azure-LI-BYOS-Production Image SLES15-SP7-SAP-Azure-VLI-BYOS-Production Affected
SUSE Liberty Linux 10 Fixed
SUSE Liberty Linux 8 Fixed
SUSE Liberty Linux 9 Fixed
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed

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CVE-2026-4700 vulnerability details – vuln.today

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