CVE-2021-0236Junos OS: A specific BGP VPNv6 flowspec message causes routing protocol daemon (rpd) process to crash with a core.
- 6.5MediumCVSS base score
- 0.88%Exploitation in 30 daysEPSS · top 40% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
Due to an improper check for unusual or exceptional conditions in Juniper Networks Junos OS and Junos OS Evolved the Routing Protocol Daemon (RPD) service, upon receipt of a specific matching BGP packet meeting a specific term in the flowspec configuration, crashes and restarts causing a Denial of Service (DoS). Continued receipt and processing of this packet will create a sustained Denial of Service (DoS) condition. This issue affects only Multiprotocol BGP (MP-BGP) VPNv6 FlowSpec deployments. This issue affects: Juniper Networks Junos OS: 18.4 versions prior to 18.4R1-S8, 18.4R2-S7, 18.4R3-S7; 19.1 versions prior to 19.1R2-S2, 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, 20.1R3; 20.2 versions prior to 20.2R2, 20.2R3; 20.3 versions prior to 20.3R1-S1, 20.3R2. Juniper Networks Junos OS Evolved: All versions after 18.4R1-EVO prior to 20.3R2-EVO. This issue does not affect: Juniper Networks Junos OS versions prior to 18.4R1. Juniper Networks Junos OS Evolved versions prior to 18.4R1-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 | Medium6.5 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
| NVDNVD · Modified | 3.1 | Medium6.5 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.88% · top 40% of all CVEs (14 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.5.
Affected products
- unaffected unspecified – < 18.4R1
- affected 18.4 – < 18.4R1-S8, 18.4R2-S7, 18.4R3-S7
- affected 19.1 – < 19.1R2-S2, 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, 20.1R3, 20.1R3-EVO
- affected 20.2 – < 20.2R2, 20.2R3, 20.2R3-EVO
- affected 20.3 – < 20.3R1-S1, 20.3R2, 20.3R2-EVO
Juniper Networks · Junos OS Evolved
- unaffected unspecified – < 18.4R1-EVO
- affected 20.3-EVO – < 20.3R2-EVO
What to do
Solution: The following software releases have been updated to resolve this specific issue: Junos OS: 18.4R1-S8, 18.4R2-S7, 18.4R3-S7, 19.1R2-S2, 19.1R3-S4, 19.2R1-S6, 19.2R3-S2, 19.3R3-S2, 19.4R2-S4, 19.4R3-S1, 20.1R2, 20.1R3, 20.2R2, 20.2R3, 20.3R1-S1, 20.3R2, 20.4R1 and all subsequent releases. Junos OS Evolved: 20.3R2-EVO, 20.4R1-EVO, and all subsequent releases.
Workaround: Do not configure "family inet6-vpn flow" under BGP if no inet6-vpn routes are required to be received.
Exploitation: Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
References
References1
- https://kb.juniper.net/JSA11131 (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-2021-2855 (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-2021-0236)Record last updated .