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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.

7.5 High

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

1.28%Up 0.8 points since Apr 14, 2021
90%50%10%1%

What each source reports

CVE List Score used 7.5

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.

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.

Record
CVE-2021-0207
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-436, CWE-115
Updated
2026-11-02
EUVDEUVD-2021-2826 7.5

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.

Record
EUVD-2021-2826
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-03
GitHub AdvisoriesGHSA-qhwr-mfcx-qrr9 No score

An improper interpretation conflict of certain data between certain software components within...

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.

Record
GHSA-qhwr-mfcx-qrr9
Weakness
CWE-436
Updated
2026-11-02
NVD 7.5

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.

Record
CVE-2021-0207
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness
CWE-115, CWE-436
Updated
2026-11-02

Affected products

History

History
RecordedChangedSources
aliases, publishedEUVD
first indexedCVE List, GitHub Advisories, NVD

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-0207 is a high vulnerability (CVSS 7.5) in Juniper Junos, published January 15, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.28%, the 70th percentile. No source names a fixed version.

References

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