CVE-2021-0259

Underlay denial of service via overlay traffic misclassification

Published Apr 22, 2021 · Updated Sep 16, 2024

Denial of service in Junos OS and Junos OS Evolved allows remote attackers to disrupt QFX5K underlay L2 traffic via overlay traffic. The DDoS protection logic incorrectly classifies high-rate legitimate overlay traffic after the default aggregate threshold is exceeded, causing the leaf to stop processing certain L2 traffic from underlay spines. Reachability requires a client on the VXLAN overlay, and continued high-volume traffic sustains the service interruption.

CVSS severity7.4
High
EPSS probability0.38%
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 Junos OS and Junos OS Evolved allows remote attackers to disrupt QFX5K underlay L2 traffic via overlay traffic. The DDoS protection logic incorrectly classifies high-rate legitimate overlay traffic after the default aggregate threshold is exceeded, causing the leaf to stop processing certain L2 traffic from underlay spines. Reachability requires a client on the VXLAN overlay, and continued high-volume traffic sustains the service interruption.

The record

CVE
CVE-2021-0259
Published
Apr 22, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS Evolved
Classifications
CWE-755, T1498
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=unspecified <20.3R2-EVO

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OS Evolvedversion=unspecified <20.3R2-EVO
Juniper Networks · Junos OSversion=17.3 <17.3R3-S11; version=17.4 <17.4R3-S5; version=18.1 <18.1R3-S13; version=18.2 <18.2R2-S8, 18.2R3-S8; version=18.3 <18.3R3-S5; version=18.4 <18.4R1-S8, 18.4R2-S6, 18.4R3-S6; version=19.1 <19.1R3-S4; version=19.2 <19.2R1-S6, 19.2R3-S2; version=19.3 <19.3R3-S2; version=19.4 <19.4R2-S4, 19.4R3-S1; version=20.1 <20.1R2; version=20.2 <20.2R2; version=20.3 <20.3R1-S2, 20.3R2

Published CVSS scores

3.3NIST NVDAV:A/AC:L/Au:N/C:N/I:N/A:P
7.4Juniper NetworksCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

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.

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No observations available

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

Weakness, pattern, technique

CWE-755Improper Handling of Exceptional Conditions
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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