CVE-2021-0207Network attack vector

Traffic interruption via cross-VLAN interpretation conflict

Published Jan 15, 2021 · Updated Sep 17, 2024

Denial of service in Juniper Networks Junos OS 17.3 through 19.4 allows remote attackers to interrupt forwarded IPv4 and IPv6 traffic. On affected NFX and EX/QFX devices, ingress filtering and egress forwarding components interpret crafted nonstandard traffic differently, causing packets redirected between VLANs to be discarded rather than forwarded. The device must pass traffic between two differently tagged VLAN interfaces; affected flows stop while the device remains operational.

CVSS severity7.5
High
EPSS probability1.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Juniper Networks Junos OS 17.3 through 19.4 allows remote attackers to interrupt forwarded IPv4 and IPv6 traffic. On affected NFX and EX/QFX devices, ingress filtering and egress forwarding components interpret crafted nonstandard traffic differently, causing packets redirected between VLANs to be discarded rather than forwarded. The device must pass traffic between two differently tagged VLAN interfaces; affected flows stop while the device remains operational.

The record

CVE
CVE-2021-0207
Published
Jan 15, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-115, CWE-436, T1498
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=17.3 <17.3R3-S7
  2. Affected versionversion=17.4 <17.4R2-S11, 17.4R3-S3
  3. Affected versionversion=18.1 <18.1R3-S9
  4. Affected versionversion=18.2 <18.2R3-S3
  5. Affected versionversion=18.3 <18.3R3-S1
  6. Affected versionversion=18.4 <18.4R1-S5, 18.4R2-S3, 18.4R3
  7. Affected versionversion=19.1 <19.1R1-S5, 19.1R2-S1, 19.1R3
  8. Affected versionversion=19.2 <19.2R1-S5, 19.2R2
  9. Affected versionversion=19.3 <19.3R2-S3, 19.3R3
  10. Affected versionversion=19.4 <19.4R1-S2, 19.4R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=17.3 <17.3R3-S7; version=17.4 <17.4R2-S11, 17.4R3-S3; version=18.1 <18.1R3-S9; version=18.2 <18.2R3-S3; version=18.3 <18.3R3-S1; version=18.4 <18.4R1-S5, 18.4R2-S3, 18.4R3; version=19.1 <19.1R1-S5, 19.1R2-S1, 19.1R3; version=19.2 <19.2R1-S5, 19.2R2; version=19.3 <19.3R2-S3, 19.3R3; version=19.4 <19.4R1-S2, 19.4R2

Published CVSS scores

7.5Juniper NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NISTAV:N/AC:L/Au:N/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-115Misinterpretation of Input
CWE-436Interpretation Conflict
T1498Network Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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