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CVE-2021-0259

Junos OS and Junos OS Evolved: QFX5K Series: Underlay network traffic might not be processed upon receipt of high rate of specific genuine overlay packets in VXLAN scenario

High7.4EPSS 0.38%
Published
Updated
Reserved
Assigned by
juniper

Description

Due to a vulnerability in DDoS protection in Juniper Networks Junos OS and Junos OS Evolved on QFX5K Series switches in a VXLAN configuration, instability might be experienced in the underlay network as a consequence of exceeding the default ddos-protection aggregate threshold. If an attacker on a client device on the overlay network sends a high volume of specific, legitimate traffic in the overlay network, due to an improperly detected DDoS violation, the leaf might not process certain L2 traffic, sent by spines in the underlay network. Continued receipt and processing of the high volume traffic will sustain the Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS on QFX5K Series: 17.3 versions prior to 17.3R3-S11; 17.4 versions prior to 17.4R3-S5; 18.1 versions prior to 18.1R3-S13; 18.2 versions prior to 18.2R2-S8, 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R1-S8, 18.4R2-S6, 18.4R3-S6; 19.1 versions prior to 19.1R3-S4; 19.2 versions prior to 19.2R1-S6, 19.2R3-S2; 19.3 versions prior to 19.3R3-S2; 19.4 versions prior to 19.4R2-S4, 19.4R3-S1; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R2; 20.3 versions prior to 20.3R1-S2, 20.3R2. Juniper Networks Junos OS Evolved on QFX5220: All versions prior to 20.3R2-EVO.

Scores

CVSS scores of CVE-2021-0259, by who scored it
Scored byCVSSScoreVector
juniperCNA (assigner)3.1High7.4CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
NVDNVD · Modified3.1High7.4CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
EPSS (exploitation in 30 days)
0.38% · top 68% of all CVEs (7 Nov 2026)
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.4.

Weakness

Affected products

  • Juniper Networks · Junos OS

    • affected 17.3 – < 17.3R3-S11
    • affected 17.4 – < 17.4R3-S5
    • affected 18.1 – < 18.1R3-S13
    • affected 18.2 – < 18.2R2-S8, 18.2R3-S8
    • affected 18.3 – < 18.3R3-S5
    • affected 18.4 – < 18.4R1-S8, 18.4R2-S6, 18.4R3-S6
    • affected 19.1 – < 19.1R3-S4
    • affected 19.2 – < 19.2R1-S6, 19.2R3-S2
    • affected 19.3 – < 19.3R3-S2
    • affected 19.4 – < 19.4R2-S4, 19.4R3-S1
    • affected 20.1 – < 20.1R2
    • affected 20.2 – < 20.2R2
    • affected 20.3 – < 20.3R1-S2, 20.3R2

  • Juniper Networks · Junos OS Evolved

    • affected unspecified – < 20.3R2-EVO

What to do

Solution: The following software releases have been updated to resolve this specific issue: Junos OS: 17.3R3-S11, 17.4R3-S5, 18.1R3-S13, 18.2R2-S8, 18.2R3-S8, 18.3R3-S5, 18.4R1-S8, 18.4R2-S6, 18.4R3-S6, 19.1R3-S4, 19.2R1-S6, 19.2R3-S2, 19.3R3-S2, 19.4R2-S4, 19.4R3-S1, 20.1R2, 20.2R2, 20.3R1-S2, 20.3R2, 20.4R1, and all subsequent releases. Junos OS Evolved: 20.3R2-EVO, 20.4R1-EVO, and all subsequent releases.

Workaround: There are no available workarounds for this issue.

Exploitation: Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

References (1)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .