An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (pfe) of Juniper Networks Junos OS on MX Series allows an unauthenticated, network-based attacker to bypass the configured firewall filter and access the control-plane of the device.
On MX platforms with
MPC10, MPC11, LC4800 or LC9600
line cards, and MX304, firewall filters applied on a loopback interface lo0.n (where n is a non-0 number) don't get executed when lo0.n is in the global VRF / default routing-instance.
An affected configuration would be:
user@host# show configuration interfaces lo0 | display set
set interfaces lo0 unit 1 family inet filter input <filter-name>
where a firewall filter is applied to a non-0 loopback interface, but that loopback interface is not referred to in any routing-instance (RI) configuration, which implies that it's used in the default RI.
The issue can be observed with the CLI command:
user@device> show firewall counter filter <filter_name>
not showing any matches.
This issue affects Junos OS on MX Series:
* all versions before 23.2R2-S6,
* 23.4 versions before 23.4R2-S7,
* 24.2 versions before 24.2R2,
* 24.4 versions before 24.4R2.
CVSS Score
6.9
EPSS Score
0.002
Published
2026-04-09
An Improper Check or Handling of Exceptional Conditions vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated, adjacent attacker to cause a Denial of Service (DoS).
If an attacker sends a specific MPLS packet, which upon processing, causes an internal loop, that leads to a PFE crash and restart. Continued receipt of these packets leads to a sustained Denial of Service (DoS) condition.
Circuit cross-connect (CCC) needs to be configured on the device for it to be affected by this issue.
This issue only affects MX Series with MPC10, MPC11, LC9600, and MX304.
This issue affects:
Juniper Networks Junos OS
21.4 versions from 21.4R3 earlier than 21.4R3-S5;
22.2 versions from 22.2R2 earlier than 22.2R3-S2;
22.3 versions from 22.3R1 earlier than 22.3R2-S2;
22.3 versions from 22.3R3 earlier than 22.3R3-S1
22.4 versions from 22.4R1 earlier than 22.4R2-S2, 22.4R3;
23.2 versions earlier than 23.2R1-S1, 23.2R2.
CVSS Score
7.1
EPSS Score
0.003
Published
2024-04-12