CVE-2021-0228: An improper check for unusual or exceptional conditions vulnerability in Juniper Networks MX Series platforms with Trio-based MPC (Modular Port Concen...

Description

An improper check for unusual or exceptional conditions vulnerability in Juniper Networks MX Series platforms with Trio-based MPC (Modular Port Concentrator) deployed in (Ethernet VPN) EVPN-(Virtual Extensible LAN) VXLAN configuration, may allow an attacker sending specific Layer 2 traffic to cause Distributed Denial of Service (DDoS) protection to trigger unexpectedly, resulting in traffic impact. Continued receipt and processing of this specific Layer 2 frames will sustain the Denial of Service (DoS) condition. An indication of compromise is to check DDOS LACP violations: user@device> show ddos-protection protocols statistics brief | match lacp This issue only affects the MX Series platforms with Trio-based MPC. No other products or platforms are affected. This issue affects: Juniper Networks Junos OS on MX Series: 15.1 versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S11; 17.4 versions prior to 17.4R3-S4; 18.1 versions prior to 18.1R3-S12; 18.2 versions prior to 18.2R2-S8, 18.2R3-S8; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S7, 18.4R3-S7; 19.1 versions prior to 19.1R3-S4; 19.2 versions prior to 19.2R1-S6; 19.3 versions prior to 19.3R3-S2; 19.4 versions prior to 19.4R2-S4, 19.4R3-S2; 20.1 versions prior to 20.1R2, 20.1R3; 20.2 versions prior to 20.2R2-S1, 20.2R3; 20.3 versions prior to 20.3R1-S1, 20.3R2;

Metrics

CVSS 3.1

6.5/10

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

EPSS Probability

0.40%

32.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions	Update
Juniper	Junos	15.1	—
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

References

https://kb.juniper.net/JSA11123Vendor Advisory
https://kb.juniper.net/JSA11123Vendor Advisory

Timeline

Published: Apr 22, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-0228?

An improper check for unusual or exceptional conditions vulnerability in Juniper Networks MX Series platforms with Trio-based MPC (Modular Port Concentrator) deployed in (Ethernet VPN) EVPN-(Virtual Extensible LAN) VXLAN configuration, may allow an attacker sending specific Layer 2 traffic to cause Distributed Denial of Service (DDoS) protection to trigger unexpectedly, resulting in traffic impact. Continued receipt and processing of this specific Layer 2 frames will sustain the Denial of Service (DoS) condition. An indication of compromise is to check DDOS LACP violations: user@device> show ddos-protection protocols statistics brief | match lacp This issue only affects the MX Series platforms with Trio-based MPC. No other products or platforms are affected. This issue affects: Juniper Networks Junos OS on MX Series: 15.1 versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S11; 17.4 versions prior to 17.4R3-S4; 18.1 versions prior to 18.1R3-S12; 18.2 versions prior to 18.2R2-S8, 18.2R3-S8; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S7, 18.4R3-S7; 19.1 versions prior to 19.1R3-S4; 19.2 versions prior to 19.2R1-S6; 19.3 versions prior to 19.3R3-S2; 19.4 versions prior to 19.4R2-S4, 19.4R3-S2; 20.1 versions prior to 20.1R2, 20.1R3; 20.2 versions prior to 20.2R2-S1, 20.2R3; 20.3 versions prior to 20.3R1-S1, 20.3R2;

How severe is CVE-2021-0228?

CVE-2021-0228 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.40% probability of exploitation in the next 30 days.

How do I fix CVE-2021-0228?

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.