What is CVE-2021-0236?

CVE-2021-0236 is a medium-severity vulnerability in Juniper Junos, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 6.5/10. Published 2021-04-22.

How severe is CVE-2021-0236?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Juniper Junos

CVE-2021-0236

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.

Published 2021-04-22 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.008 (56.5th percentile), scored 2026-10-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 56th percentile — 56.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

Juniper Junos — versions 18.4, 19.1, 19.2
Juniper Junos OS Evolved — versions 19.1, 19.2, 19.3
Juniper Networks Junos OS — versions unspecified, 18.4, 19.1
Juniper Networks Junos OS Evolved — versions unspecified, 20.3-EVO

Weakness classification (CWE)

CWE-754 — Improper Check for Unusual or Exceptional Conditions

References

kb.juniper.net/JSA11131 (Vendor Advisory)

Frequently asked questions

What is CVE-2021-0236?: CVE-2021-0236 is a medium-severity vulnerability in Juniper Junos, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 6.5/10. Published 2021-04-22.
How severe is CVE-2021-0236?: Medium severity. CVSS v3 base score is 6.5 out of 10.