CVE-2026-57019: Junos OS: MX Series: Specific traffic causes an FPC to reset

An Improper Validation of Specified Quantity in Input vulnerability in the Packet Forwarding Engine (pfe) of Juniper Networks Junos OS on MX Series allows an unauthenticated, adjacent attacker to cause a Denial-of-Service (DoS).

When a specific packet is received from device in the same broadcast domain, an affected system calculates the packet size incorrectly. This causes further packet processing to fail, which triggers an FPC major error, resulting in a FPC reset impacting traffic until the FPC has automatically recovered.

Affected scenarios are: MAP-T, or non-IP traffic encapsulated in IP (e.g. MPLS over GRE).

When this issue happens the following logs can be observed:

fpc<#> CMError: /fpc/0/pfe/0/cm/0/MQSS(0)/0/MQSSCMERRORLIINTREGUNROLLTAILLENGTHOVF (0x2205eb), scope: pfe, category: functional, severity: major, module: MQSS(0), type: LI: Unroll TAIL length overflow, occategory: default fpc<#> Performing action reset-fru for error /fpc/0/pfe/0/cm/0/MQSS(0)/0/MQSSCMERRORLIINTREGUNROLLTAILLENGTHOVF (0x2205eb) in module: MQSS(0) with scope: pfe category: functional level: major, occategory: default

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-S4, 24.4 versions before 24.4R2-S4, 25.2 versions before 25.2R2.