An input validation causes the system to incorrectly calculate packet sizes for certain traffic types. When a specific packet is received from another device in the same broadcast domain—such as MAP‑T traffic or non‑IP traffic encapsulated in IP (e.g., MPLS over GRE)—the calculation overflows. The resulting failure in packet processing triggers an FPC major error, causing the FPC to reset and interrupt traffic until the hardware automatically recovers. This creates a denial‑of‑service that affects all traffic handled by the reset FPC. The weakness is classified as CWE‑1284.

Juniper Networks Junos OS running on MX Series devices with software versions earlier than 23.2R2‑S6, 23.4R2‑S7, 24.2R2‑S4, 24.4R2‑S4, and 25.2R2, as well as any releases before those update milestones; the issue is specifically triggered by MAP‑T traffic or non‑IP traffic encapsulated within IP such as MPLS over GRE in the same broadcast domain.

The vulnerability scores 7.1 on the CVSS scale and has an EPSS score of less than 1%, indicating a low but non‑zero exploitation probability. It is not listed in CISA’s KEV catalog. The flaw requires an unauthenticated attacker adjacent to the device on the same broadcast domain, who can craft packets that trigger the faulty size calculation, causing an FPC reset and an immediate denial‑of‑service that automatically resolves after the hardware recovers.