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CVE Record

CVE-2019-0048: EX4300 Series: When a firewall filter is applied to a loopback interface, other firewall filters for multicast traffic may fail

On EX4300 Series switches with TCAM optimization enabled, incoming multicast traffic matches an implicit loopback filter rule first, since it has high priority. This rule is meant for reserved multicast addresses 224.0.0.x, but incorrectly matches on 224.x.x.x. Due to this bug, when a firewall filter is applied on the loopback interface, other firewall filters might stop working for multicast traffic. The command 'show firewall filter' can be used to confirm whether the filter is working. This issue only affects the EX4300 switch. No other products or platforms are affected by this vulnerability. This issue affects: Juniper Networks Junos OS: 14.1X53 versions prior to 14.1X53-D51, 14.1X53-D115 on EX4300 Series; 17.1 versions prior to 17.1R3 on EX4300 Series; 17.2 versions prior to 17.2R3-S2 on EX4300 Series; 17.3 versions prior to 17.3R3-S3 on EX4300 Series; 17.4 versions prior to 17.4R2-S5, 17.4R3 on EX4300 Series; 18.1 versions prior to 18.1R3-S1 on EX4300 Series; 18.2 versions prior to 18.2R2 on EX4300 Series; 18.3 versions prior to 18.3R2 on EX4300 Series.

MediumCVSS 5.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Certain Juniper EX4300 switches can mishandle multicast filtering when a firewall filter is applied to the loopback interface. Traffic that should be evaluated by configured multicast filters may instead match an internal high-priority loopback rule, reducing intended filtering control.

Executive priority

Prioritize during normal network maintenance unless multicast filtering protects sensitive segmentation or operational controls. Escalate where EX4300 multicast filtering is part of security enforcement.

Technical view

With TCAM optimization enabled on EX4300, an implicit loopback filter intended for 224.0.0.x incorrectly matches 224.x.x.x multicast traffic. When a loopback firewall filter is present, other firewall filters may stop working for multicast traffic. Only EX4300 is listed as affected.

Likely exposure

Exposure is limited to Juniper EX4300 switches running affected Junos OS versions, with TCAM optimization enabled and loopback firewall filtering in use. Other Juniper products and platforms are stated as unaffected.

Exploitation context

The source bundle does not show KEV listing or public active exploitation evidence. The issue is remotely reachable by CVSS, but the documented impact is limited integrity loss in multicast firewall filtering behavior.

Researcher notes

The affected condition is configuration-dependent. Evidence names EX4300 only, specific Junos OS trains, TCAM optimization, loopback filtering, and multicast 224.x.x.x matching behavior. Do not generalize to other Juniper platforms.

Mitigation direction

  • Inventory EX4300 switches and compare Junos OS versions against the affected ranges.
  • Upgrade affected EX4300 devices to a Junos OS release at or beyond the listed fixed versions.
  • Review loopback firewall filters and multicast filter dependencies on affected switches.
  • Check Juniper JSA10942 for current vendor guidance before operational changes.

Validation and detection

  • Confirm whether each EX4300 has TCAM optimization enabled.
  • Identify loopback interfaces with firewall filters applied.
  • Verify multicast firewall filters are matching as intended using vendor-supported filter status output.
  • Check whether Junos OS is older than the fixed release for its train.
Prepared
Confidence
high
Sources
3

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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CVE-2019-0048 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.8 (3.0)
Known Exploited
No
Published

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
5.8CVSS 3.0MediumCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N3.91.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.0 score

5.8Medium
CVSS 3.0 vector shape for CVE-2019-0048Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Juniper NetworksJunos OS14.1X53 versions prior to 14.1X53-D51 and 14.1X53-D115 on EX4300 Series, 17.1 versions prior to 17.1R3 on EX4300 Series, 17.2 versions prior to 17.2R3-S2 on EX4300 Series, 17.3 versions prior to 17.3R3-S3 on EX4300 Series, 17.4 versions prior to 17.4R2-S5 and 17.4R3 on EX4300 Series, 18.1 versions prior to 18.1R3-S1 on EX4300 Series, 18.2 versions prior to 18.2R2 on EX4300 Series, 18.3 versions prior to 18.3R2 on EX4300 SeriesListed
Weakness

CWE details

CWE-200

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Exposure of Sensitive Information to an Unauthorized Actor

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