CVE-2021-31370
Junos OS: QFX5000 Series and EX4600 Series: Control traffic might be dropped if a high rate of specific multicast traffic is received
- Published
- Updated
- Reserved
- Assigned by
- juniper
Description
An Incomplete List of Disallowed Inputs vulnerability in Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on QFX5000 Series and EX4600 Series allows an adjacent unauthenticated attacker which sends a high rate of specific multicast traffic to cause control traffic received from the network to be dropped. This will impact control protocols (including but not limited to routing-protocols) and lead to a Denial of Service (DoS). Continued receipt of this specific multicast traffic will create a sustained Denial of Service (DoS) condition. This issue affects Juniper Networks Junos OS on QFX5000 and EX4600 Series: All versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S6; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S3; 19.4 versions prior to 19.4R1-S4, 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2-S2, 20.4R3; 21.1 versions prior to 21.1R1-S1, 21.1R2.
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 | Medium6.5 | CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| NVDNVD · Modified | 3.1 | Medium6.5 | CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.42% · top 63% of all CVEs (7 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.5.
Weakness
Affected products
- affected unspecified – < 17.3R3-S12
- affected 17.4 – < 17.4R3-S5
- affected 18.3 – < 18.3R3-S5
- affected 18.4 – < 18.4R3-S9
- affected 19.1 – < 19.1R3-S6
- affected 19.2 – < 19.2R1-S7, 19.2R3-S3
- affected 19.3 – < 19.3R2-S6, 19.3R3-S3
- affected 19.4 – < 19.4R1-S4, 19.4R3-S3
- affected 20.1 – < 20.1R2-S2, 20.1R3-S1
- affected 20.2 – < 20.2R3-S2
- affected 20.3 – < 20.3R3
- affected 20.4 – < 20.4R2-S2, 20.4R3
- affected 21.1 – < 21.1R1-S1, 21.1R2
What to do
Solution: The following software releases have been updated to resolve this specific issue: 17.3R3-S12, 17.4R3-S5, 18.3R3-S5, 18.4R3-S9, 19.1R3-S6, 19.2R1-S7, 19.2R3-S3, 19.3R2-S6, 19.3R3-S3, 19.4R1-S4, 19.4R3-S3, 20.1R2-S2, 20.1R3-S1, 20.2R3-S2, 20.3R3, 20.4R2-S2, 20.4R3, 21.1R1-S1, 21.1R2, 21.2R1, and all subsequent releases.
Workaround: Please ensure you have a loopback filter applied to drop unneeded multicast traffic. You can find further information on such filters in https://www.rfc-editor.org/rfc/rfc6192 and in "Hardening Junos Devices, 2nd Edition" at https://www.juniper.net/documentation/jnbooks/us/en/day-one-books
Exploitation: Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
References (1)
- https://kb.juniper.net/JSA11232 (opens in a new tab)x_refsource_CONFIRMx_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)
- 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://trackcve.app/cve/CVE-2021-31370)Record last updated .