CVE-2020-1633: Due to a new NDP proxy feature for EVPN leaf nodes introduced in Junos OS 17.4, crafted NDPv6 packets could transit a Junos device configured as a Bro...

Description

Due to a new NDP proxy feature for EVPN leaf nodes introduced in Junos OS 17.4, crafted NDPv6 packets could transit a Junos device configured as a Broadband Network Gateway (BNG) and reach the EVPN leaf node, causing a stale MAC address entry. This could cause legitimate traffic to be discarded, leading to a Denial of Service (DoS) condition. This issue only affects Junos OS 17.4 and later releases. Prior releases do not support this feature and are unaffected by this vulnerability. This issue only affects IPv6. IPv4 ARP proxy is unaffected by this vulnerability. This issue affects Juniper Networks Junos OS: 17.4 versions prior to 17.4R2-S9, 17.4R3 on MX Series; 18.1 versions prior to 18.1R3-S9 on MX Series; 18.2 versions prior to 18.2R2-S7, 18.2R3-S3 on MX Series; 18.2X75 versions prior to 18.2X75-D33, 18.2X75-D411, 18.2X75-D420, 18.2X75-D60 on MX Series; 18.3 versions prior to 18.3R1-S7, 18.3R2-S3, 18.3R3 on MX Series; 18.4 versions prior to 18.4R1-S5, 18.4R2-S2, 18.4R3 on MX Series; 19.1 versions prior to 19.1R1-S4, 19.1R2 on MX Series; 19.2 versions prior to 19.2R1-S3, 19.2R2 on MX Series.

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

0.51%

39.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-20

Affected Software

Vendor	Product	Versions
Juniper	Junos	17.4
Juniper	Junos	18.1
Juniper	Junos	18.2
Juniper	Junos	18.2x75
Juniper	Junos	18.3
Juniper	Junos	18.4
Juniper	Junos	19.1
Juniper	Junos	19.2

References

https://kb.juniper.net/JSA11012Vendor Advisory
https://kb.juniper.net/JSA11012Vendor Advisory

Timeline

Published: Apr 9, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2020-1633?

Due to a new NDP proxy feature for EVPN leaf nodes introduced in Junos OS 17.4, crafted NDPv6 packets could transit a Junos device configured as a Broadband Network Gateway (BNG) and reach the EVPN leaf node, causing a stale MAC address entry. This could cause legitimate traffic to be discarded, leading to a Denial of Service (DoS) condition. This issue only affects Junos OS 17.4 and later releases. Prior releases do not support this feature and are unaffected by this vulnerability. This issue only affects IPv6. IPv4 ARP proxy is unaffected by this vulnerability. This issue affects Juniper Networks Junos OS: 17.4 versions prior to 17.4R2-S9, 17.4R3 on MX Series; 18.1 versions prior to 18.1R3-S9 on MX Series; 18.2 versions prior to 18.2R2-S7, 18.2R3-S3 on MX Series; 18.2X75 versions prior to 18.2X75-D33, 18.2X75-D411, 18.2X75-D420, 18.2X75-D60 on MX Series; 18.3 versions prior to 18.3R1-S7, 18.3R2-S3, 18.3R3 on MX Series; 18.4 versions prior to 18.4R1-S5, 18.4R2-S2, 18.4R3 on MX Series; 19.1 versions prior to 19.1R1-S4, 19.1R2 on MX Series; 19.2 versions prior to 19.2R1-S3, 19.2R2 on MX Series.

How severe is CVE-2020-1633?

CVE-2020-1633 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.51% probability of exploitation in the next 30 days.

How do I fix CVE-2020-1633?

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.