CVE-2026-33800

Summary

An Unchecked Input for Loop Condition 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).Micro-BFD session flaps generate respective up/down events which are queued by PFEMAN for processing. Especially in a Virtual-Chassis (VC) scenario with locality‑bias configured, processing takes a significant amount of time for each event. If these sessions keep flapping, new events are constantly added, and in turn PFEMAN never completes processing these events. This results in the PFEMAN watchdog timer expiring, which causes the FPC to crash and restart, representing a complete service outage.

This issue only affects MX series FPCs up to and including MPC9. It does not affect MPC10/11, LC4800/9600 and MX304.

This issue affects Junos OS on MX Series:

  • all versions before 23.2R2-S7,
  • 23.4 versions before 23.4R2-S8,
  • 24.2 versions before 24.2R2-S4,
  • 24.4 versions before 24.4R2-S3,
  • 25.2 versions before 25.2R2.

Affected Software

VendorProductVersion RangeStatus
Juniper NetworksJunos OS0 < 23.2R2-S7affected
Juniper NetworksJunos OS23.4 < 23.4R2-S8affected
Juniper NetworksJunos OS24.2 < 24.2R2-S4affected
Juniper NetworksJunos OS24.4 < 24.4R2-S3affected
Juniper NetworksJunos OS25.2 < 25.2R2affected

Weaknesses

  • CWE-606: CWE-606 Unchecked Input for Loop Condition

Workarounds

To reduce the risk of exploitation, configure BFD with an increased holddown-timer, so that the queued events can be processed before a new up event occurs:

[ … bfd-liveness-detection holddown-interval milliseconds <value> ]

References