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CVE Record

CVE-2021-0295: Junos OS: QFX10K Series: Denial of Service (DoS) upon receipt of DVMRP packets received on multi-homing ESI in VXLAN.

A vulnerability in the Distance Vector Multicast Routing Protocol (DVMRP) of Juniper Networks Junos OS on the QFX10K Series switches allows an attacker to trigger a packet forwarding loop, leading to a partial Denial of Service (DoS). The issue is caused by DVMRP packets looping on a multi-homed Ethernet Segment Identifier (ESI) when VXLAN is configured. DVMRP packets received on a multi-homed ESI are sent to the peer, and then incorrectly forwarded out the same ESI, violating the split horizon rule. This issue only affects QFX10K Series switches, including the QFX10002, QFX10008, and QFX10016. Other products and platforms are unaffected by this vulnerability. This issue affects Juniper Networks Junos OS on QFX10K Series: 17.3 versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R3-S5; 18.1 versions prior to 18.1R3-S13; 18.2 version 18.2R1 and later versions; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R2-S9, 18.4R3-S8; 19.1 versions prior to 19.1R3-S5; 19.2 versions prior to 19.2R1-S7, 19.2R3-S2; 19.3 versions prior to 19.3R3-S2; 19.4 versions prior to 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R3; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2.

MediumCVSS 6.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Certain Juniper QFX10K data-center switches can mishandle DVMRP traffic when VXLAN and multi-homed ESI are configured. The result can be a forwarding loop and partial denial of service, affecting availability of parts of the switching fabric rather than causing full system compromise.

Executive priority

Treat this as a targeted infrastructure availability risk. It is not described as broadly exploitable across all Juniper products, but affected QFX10K VXLAN fabrics should be patched because a forwarding loop can disrupt data-center traffic.

Technical view

CVE-2021-0295 affects Junos OS on QFX10K Series switches. DVMRP packets received on a multi-homed ESI in a VXLAN setup may be forwarded to a peer and then back out the same ESI, violating split horizon behavior and creating a packet forwarding loop.

Likely exposure

Exposure appears limited to Juniper QFX10K Series switches, including QFX10002, QFX10008, and QFX10016, running affected Junos OS versions with VXLAN and multi-homed ESI. The source states other products and platforms are unaffected.

Exploitation context

The CVE is not listed as KEV, and the provided sources do not report active exploitation. The CVSS vector indicates adjacent-network reachability, low attack complexity, no privileges, and no user interaction, with low availability and integrity impact.

Researcher notes

Key exposure conditions are QFX10K hardware, affected Junos OS releases, VXLAN, and multi-homed ESI. The documented flaw is protocol forwarding behavior for DVMRP packets that violates split horizon. Public evidence in the bundle does not establish exploitation in the wild.

Mitigation direction

  • Upgrade affected QFX10K switches to a fixed Junos OS release listed in Juniper guidance.
  • Review Juniper JSA11208 for current vendor remediation details and release notes.
  • Prioritize switches using VXLAN with multi-homed ESI configurations.
  • Track remediation through normal change control because this affects switching availability.
  • Do not assume non-QFX10K platforms are affected unless Juniper updates guidance.

Validation and detection

  • Inventory QFX10002, QFX10008, and QFX10016 devices in the environment.
  • Confirm Junos OS versions against the affected version ranges.
  • Check whether VXLAN and multi-homed ESI are configured on those switches.
  • Review monitoring for partial DoS symptoms consistent with forwarding loops.
  • After upgrade, confirm devices run a fixed Junos OS release.
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

Conservative CVE-to-ATT&CK context

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ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-697: Exact CWE lookup

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cve · low confidence lookup

CVE-2021-0295 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:L

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
6.1CVSS 3.1MediumCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:L2.82.7Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.1Medium
CVSS 3.1 vector shape for CVE-2021-0295Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:L

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 OS17.3, 17.4, 18.1, 18.2R1, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3, 20.4Listed
Weakness

CWE details

CWE-697

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-697 · source CWE mapping

Incorrect Comparison

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