CVE-2021-0259Junos 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
- 7.4HighCVSS base score
- 0.40%Exploitation in 30 daysEPSS · top 66% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By juniper
- 6 months later
· 6 months later
Published
- 3 years later
· 3 years later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| juniperCNA (assigner) | 3.1 | High7.4 | CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H |
| NVDNVD · Modified | 3.1 | High7.4 | CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.40% · top 66% of all CVEs (13 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.4.
Affected products
- 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
References1
- https://kb.juniper.net/JSA11150 (opens in a new tab)x_refsource_MISCx_transferred
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2021-2878 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2021-0259)Record last updated .