CVE-2021-0207

NFX250, NFX350, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series: Certain genuine traffic received by the Junos OS device will be discarded instead of forwarded.

HIGH

7.5

CVSS Score

Published: January 15, 2021 at 05:35 PM UTC

Updated: June 17, 2026 at 03:29 AM UTC

14 products affected across 2 vendorsJunosQfx5200Qfx5110

Using Junos OS by Juniper Networks?

Get instant alerts when new vulnerabilities affect Junos OS - before attackers find them.

Real-time alertsTrack your software stackFree plan available

Start Free Sign In

Severity

HIGH7.5

Exploit prediction

EPSS 1%

Description

An improper interpretation conflict of certain data between certain software components within the Juniper Networks Junos OS devices does not allow certain traffic to pass through the device upon receipt from an ingress interface filtering certain specific types of traffic which is then being redirected to an egress interface on a different VLAN. This causes a Denial of Service (DoS) to those clients sending these particular types of traffic. Such traffic being sent by a client may appear genuine, but is non-standard in nature and should be considered as potentially malicious, and can be targeted to the device, or destined through it for the issue to occur. This issues affects IPv4 and IPv6 traffic. An indicator of compromise may be found by checking log files. You may find that traffic on the input interface has 100% of traffic flowing into the device, yet the egress interface shows 0 pps leaving the device. For example: [show interfaces "interface" statistics detail] Output between two interfaces would reveal something similar to: Ingress, first interface: -------------------- Interface Link Input packets (pps) Output packets (pps) et-0/0/0 Up 9999999999 (9999) 1 (0) -------------------- Egress, second interface: -------------------- Interface Link Input packets (pps) Output packets (pps) et-0/0/1 Up 0 (0) 9999999999 (0) -------------------- Dropped packets will not show up in DDoS monitoring/protection counters as issue is not caused by anti-DDoS protection mechanisms. This issue affects: Juniper Networks Junos OS: 17.3 versions prior to 17.3R3-S7 on NFX250, QFX5K Series, EX4600; 17.4 versions prior to 17.4R2-S11, 17.4R3-S3 on NFX250, QFX5K Series, EX4600; 18.1 versions prior to 18.1R3-S9 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4600; 18.2 versions prior to 18.2R3-S3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600; 18.3 versions prior to 18.3R3-S1 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series; 18.4 versions prior to 18.4R1-S5, 18.4R2-S3, 18.4R3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series; 19.1 versions prior to 19.1R1-S5, 19.1R2-S1, 19.1R3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series; 19.2 versions prior to 19.2R1-S5, 19.2R2 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series; 19.3 versions prior to 19.3R2-S3, 19.3R3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series; 19.4 versions prior to 19.4R1-S2, 19.4R2 on NFX250, NFX350, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series. This issue does not affect Junos OS releases prior to 17.2R2.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Junos · Juniper Networks

95%

17.3 ≤ v < 17.3R3-S717.4 ≤ v < 17.4R2-S11, 17.4R3-S318.1 ≤ v < 18.1R3-S918.2 ≤ v < 18.2R3-S318.3 ≤ v < 18.3R3-S118.4 ≤ v < 18.4R1-S5, 18.4R2-S3, 18.4R319.1 ≤ v < 19.1R1-S5, 19.1R2-S1, 19.1R319.2 ≤ v < 19.2R1-S5, 19.2R219.3 ≤ v < 19.3R2-S3, 19.3R319.4 ≤ v < 19.4R1-S2, 19.4R217.3 17.3 r1-s1 17.3 r2 17.3 r2-s1 17.3 r2-s2 17.3 r2-s3 17.3 r2-s4 17.3 r2-s5 17.3 r3 17.3 r3-s1 17.3 r3-s2 17.3 r3-s3 17.3 r3-s4 17.3 r3-s5 17.3 r3-s6 17.4 17.4 r1 17.4 r1-s1 17.4 r1-s2 17.4 r1-s4 17.4 r1-s5 17.4 r1-s6 17.4 r1-s7 17.4 r2 17.4 r2-s1 17.4 r2-s10 17.4 r2-s2 17.4 r2-s3 17.4 r2-s4 17.4 r2-s5 17.4 r2-s6 17.4 r2-s7 17.4 r2-s8 17.4 r2-s9 17.4 r3 17.4 r3-s1 17.4 r3-s2 18.1 18.1 r1 18.1 r2 18.1 r2-s1 18.1 r2-s2 18.1 r2-s4 18.1 r3 18.1 r3-s1 18.1 r3-s2 18.1 r3-s3 18.1 r3-s4 18.1 r3-s6 18.1 r3-s7 18.1 r3-s8 18.2 18.2 r1 18.2 r1-s3 18.2 r1-s4 18.2 r1-s5 18.2 r2 18.2 r2-s1 18.2 r2-s2 18.2 r2-s3 18.2 r2-s4 18.2 r2-s5 18.2 r2-s6 18.2 r3 18.2 r3-s1 18.2 r3-s2 18.3 18.3 r1 18.3 r1-s1 18.3 r1-s2 18.3 r1-s3 18.3 r1-s5 18.3 r1-s6 18.3 r2 18.3 r2-s1 18.3 r2-s2 18.3 r2-s3 18.3 r2-s4 18.3 r3 18.4 18.4 r1 18.4 r1-s1 18.4 r1-s2 18.4 r1-s3 18.4 r1-s4 18.4 r2 18.4 r2-s1 18.4 r2-s2 19.1 19.1 r1 19.1 r1-s1 19.1 r1-s2 19.1 r1-s3 19.1 r1-s4 19.1 r2 19.2 19.2 r1 19.2 r1-s1 19.2 r1-s2 19.2 r1-s3 19.2 r1-s4 19.3 19.3 r1 19.3 r1-s1 19.3 r2 19.3 r2-s1 19.3 r2-s2 19.4 19.4 r1 19.4 r1-s1

Affected range stops below 17.3R3-S7, so it looks safe — our inference, not a vendor statement

Affected range stops below 17.4R2-S11, 17.4R3-S3, so it looks safe — our inference, not a vendor statement

Affected range stops below 18.1R3-S9, so it looks safe — our inference, not a vendor statement

Affected range stops below 18.2R3-S3, so it looks safe — our inference, not a vendor statement

Affected range stops below 18.3R3-S1, so it looks safe — our inference, not a vendor statement

Affected range stops below 18.4R1-S5, 18.4R2-S3, 18.4R3, so it looks safe — our inference, not a vendor statement

Affected range stops below 19.1R1-S5, 19.1R2-S1, 19.1R3, so it looks safe — our inference, not a vendor statement

Affected range stops below 19.2R1-S5, 19.2R2, so it looks safe — our inference, not a vendor statement

Affected range stops below 19.3R2-S3, 19.3R3, so it looks safe — our inference, not a vendor statement

Affected range stops below 19.4R1-S2, 19.4R2, so it looks safe — our inference, not a vendor statement

juniper-ex2300 (environment) · juniper-ex3400 (environment) · juniper-ex4300 (environment) · juniper-ex4600 (environment) · juniper-nfx250 (environment) · juniper-nfx350 (environment) · juniper-qfx5100 (environment) · juniper-qfx5110 (environment) · juniper-qfx5120 (environment) · juniper-qfx5130 (environment) · juniper-qfx5200 (environment) · juniper-qfx5210 (environment) · juniper-qfx5220 (environment)

Ex2300 · Juniperdevice

80%

All versions

Ex3400 · Juniperdevice

80%

All versions

Ex4300 · Juniperdevice

80%

All versions

Ex4600 · Juniperdevice

80%

All versions