Medium [CVE-2026-33774] 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
This medium-severity Juniper Networks advisory covers CVE-2026-33774 affecting Junos OS, Junos, MX.
Android app · Google Play
Monitor future Juniper Networks CVEs from your phone.
Choose a whole vendor or a precise platform, then receive matching security advisories by phone notification, email, or both. Coverage follows 32 official vendor sources and 160+ reviewed platform categories.
Summary
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
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
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,
Affected products named by the advisory: MX.
Affected products named by the advisory: MX.
- * all versions before 23
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
- 23.2R2-S6
- 23.4R2-S7
- 24.2R2
- 24.4R2
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Mitigation
Upgrade to a fixed release: 23.2R2-S6, 23.4R2-S7, 24.2R2, 24.4R2. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Discussion(0)
No comments yet. Share field notes, upgrade gotchas, or questions — verify against the vendor advisory before acting on community advice.
Sign in to join the discussion.