CVE-2021-0211: An improper check for unusual or exceptional conditions in Juniper Networks Junos OS and Junos OS Evolved Routing Protocol Daemon (RPD) service allows...

Description

An improper check for unusual or exceptional conditions in Juniper Networks Junos OS and Junos OS Evolved Routing Protocol Daemon (RPD) service allows an attacker to send a valid BGP FlowSpec message thereby causing an unexpected change in the route advertisements within the BGP FlowSpec domain leading to disruptions in network traffic causing a Denial of Service (DoS) condition. Continued receipt of these update messages will cause a sustained Denial of Service condition. This issue affects Juniper Networks: Junos OS: All versions prior to 17.3R3-S10 with the exceptions of 15.1X49-D240 on SRX Series and 15.1R7-S8 on EX Series; 17.3 versions prior to 17.3R3-S10; 17.4 versions prior to 17.4R2-S12, 17.4R3-S4; 18.1 versions prior to 18.1R3-S12; 18.2 versions prior to 18.2R2-S8, 18.2R3-S6; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S6, 18.4R3-S6; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3-S3; 19.2 versions prior to 19.2R3-S1; 19.3 versions prior to 19.3R2-S5, 19.3R3-S1; 19.4 versions prior to 19.4R1-S3, 19.4R2-S3, 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S3 20.2R2; 20.3 versions prior to 20.3R1-S1, 20.3R2. Junos OS Evolved: All versions prior to 20.3R1-S1-EVO, 20.3R2-EVO.

Metrics

CVSS 3.1

10/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:H

EPSS Probability

1.32%

67.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-754

Affected Software

Vendor	Product	Versions	Update
Juniper	Junos	17.3	—
Juniper	Junos	17.4	—
Juniper	Junos	18.1	—
Juniper	Junos	18.2	—
Juniper	Junos	18.3	—
Juniper	Junos	18.4	—
Juniper	Junos	19.1	—
Juniper	Junos	19.2	—
Juniper	Junos	19.3	—
Juniper	Junos	19.4	R1
Juniper	Junos	20.1	R1
Juniper	Junos	20.2	R1
Juniper	Junos	20.3	R1
Juniper	Junos Os Evolved	19.2	R1
Juniper	Junos Os Evolved	19.3	R2
Juniper	Junos Os Evolved	19.4	R1
Juniper	Junos Os Evolved	20.1	—
Juniper	Junos Os Evolved	20.2	—
Juniper	Junos Os Evolved	20.3	R1
Juniper	Junos	15.1x49	—
Juniper	Junos	15.1x49-d30	—
Juniper	Junos	15.1x49-d60	—
Juniper	Junos	15.1x49-d140	—
Juniper	Junos	15.1x49-d150	—
Juniper	Junos	15.1x49-d160	—
Juniper	Junos	15.1	—

References

https://kb.juniper.net/JSA11101Vendor Advisory
https://kb.juniper.net/JSA11101Vendor Advisory

Timeline

Published: Jan 15, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-0211?

An improper check for unusual or exceptional conditions in Juniper Networks Junos OS and Junos OS Evolved Routing Protocol Daemon (RPD) service allows an attacker to send a valid BGP FlowSpec message thereby causing an unexpected change in the route advertisements within the BGP FlowSpec domain leading to disruptions in network traffic causing a Denial of Service (DoS) condition. Continued receipt of these update messages will cause a sustained Denial of Service condition. This issue affects Juniper Networks: Junos OS: All versions prior to 17.3R3-S10 with the exceptions of 15.1X49-D240 on SRX Series and 15.1R7-S8 on EX Series; 17.3 versions prior to 17.3R3-S10; 17.4 versions prior to 17.4R2-S12, 17.4R3-S4; 18.1 versions prior to 18.1R3-S12; 18.2 versions prior to 18.2R2-S8, 18.2R3-S6; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S6, 18.4R3-S6; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3-S3; 19.2 versions prior to 19.2R3-S1; 19.3 versions prior to 19.3R2-S5, 19.3R3-S1; 19.4 versions prior to 19.4R1-S3, 19.4R2-S3, 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S3 20.2R2; 20.3 versions prior to 20.3R1-S1, 20.3R2. Junos OS Evolved: All versions prior to 20.3R1-S1-EVO, 20.3R2-EVO.

How severe is CVE-2021-0211?

CVE-2021-0211 has a CVSS score of 10/10 (CRITICAL severity). The EPSS model estimates a 1.32% probability of exploitation in the next 30 days.

How do I fix CVE-2021-0211?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.