Juniper Junos OS up to 23.2R2-S5/23.4R2-S6/24.2R1/24.4R1 Loopback Interface unusual condition

Summaryinfo

A vulnerability classified as critical has been found in Juniper Junos OS up to 23.2R2-S5/23.4R2-S6/24.2R1/24.4R1. Impacted is an unknown function of the component Loopback Interface Handler. Performing a manipulation results in unusual condition. This vulnerability is identified as CVE-2026-33774. The attack can be initiated remotely. There is not any exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in Juniper Junos OS up to 23.2R2-S5/23.4R2-S6/24.2R1/24.4R1. This affects some unknown processing of the component Loopback Interface Handler. The manipulation with an unknown input leads to a unusual condition vulnerability. CWE is classifying the issue as CWE-754. The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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, * 24.2 versions before 24.2R2, * 24.4 versions before 24.4R2.

It is possible to read the advisory at kb.juniper.net. This vulnerability is uniquely identified as CVE-2026-33774 since 03/23/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 04/10/2026).

Upgrading to version 23.2R2-S6, 23.4R2-S7, 24.2R2 or 24.4R2 eliminates this vulnerability.

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Productinfo

Type

• Router Operating System

Vendor

• Juniper

Name

• Junos OS

Version

• 23.2R2-S5
• 23.4R2-S6
• 24.2R1
• 24.4R1

License

• commercial

Website

• Vendor: https://www.juniper.net/

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