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Mozilla Firefox EUVDEUVD-2026-30919

| CVE-2026-8971 MEDIUM
Origin Validation Error (CWE-346)
2026-05-19 mozilla GHSA-wg2h-wc56-7jcc
Authentication Bypass Mozilla
6.5
CVSS 3.1 · Vendor: mozilla
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Severity by source

Vendor (mozilla) PRIMARY
6.5 MEDIUM
AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
vuln.today AI
5.4 MEDIUM

UI:R applied because victim must actively navigate to attacker page; all other metrics match network-based SOP bypass with partial C and I impact.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative
Red Hat
3.4 LOW
qualitative

Primary rating from Vendor (mozilla).

CVSS VectorVendor: mozilla

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

Lifecycle Timeline

3
Analysis Generated
Jul 23, 2026 - 17:39 vuln.today
CVE Published
May 19, 2026 - 12:30 nvd
UNKNOWN (no severity yet)
CVE Published
May 19, 2026 - 12:30 cve.org
MEDIUM 6.5

DescriptionCVE.org

Same-origin policy bypass in the Networking: JAR component. This vulnerability was fixed in Firefox 151.

AnalysisAI

Same-origin policy bypass in Firefox's Networking: JAR component (all versions prior to Firefox 151) allows unauthenticated remote attackers to cross origin boundaries, enabling limited reads from and writes to content belonging to other origins. The CVSS 6.5 Medium score reflects partial confidentiality and integrity impact without availability consequence. No public exploit has been identified and CISA SSVC reports no active exploitation, though the attack is classified as automatable, meaning scripted mass-targeting would be feasible if a POC were released.

Technical ContextAI

The JAR (Java Archive) URL scheme - a legacy mechanism that allows Firefox to load resources embedded within ZIP/JAR archives fetched over HTTP - contains an origin validation error (CWE-346) in the browser's networking layer. Firefox fails to correctly enforce same-origin policy checks when processing JAR-scheme URLs, allowing origin boundaries to be crossed. This class of flaw has precedent in Gecko-based browsers where the nested URL scheme confuses the runtime's origin comparison logic. The affected product is identified by CPE cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*, covering all Firefox versions up to (but not including) version 151. Mozilla's Bugzilla entry 2032604 and dual security advisories MFSA2026-46 and MFSA2026-50 document the root cause.

RemediationAI

Upgrade to Mozilla Firefox 151 or later, which contains the vendor-released patch for this same-origin policy bypass. Mozilla's official guidance is published at https://www.mozilla.org/security/advisories/mfsa2026-46/ and https://www.mozilla.org/security/advisories/mfsa2026-50/. Users on SUSE or Red Hat Linux should apply updated Firefox packages through their distribution's package manager once vendor-issued updates are available. If immediate upgrade is not feasible, restricting Firefox usage to trusted sites only through organizational policy reduces exposure, though this is not a technical control and does not prevent a user from inadvertently visiting a crafted page. Deploying a web content filter that blocks JAR-scheme URLs at the network perimeter can serve as a compensating control, though it may break legitimate JAR-based web applications if any are in use. There is no documented in-browser configuration flag to disable JAR URL handling without patching.

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Same weakness CWE-346 – Origin Validation Error

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Same technique Authentication Bypass

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Vendor StatusVendor

SUSE

Severity: Medium
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise Module for Desktop Applications 15 SP7 Fixed
SUSE Linux Enterprise Module for Package Hub 15 SP7 Fixed

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EUVD-2026-30919 vulnerability details – vuln.today
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