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, and LC2101/2103 and LC480. 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.

 

To be exposed to this issue an MX VC needs to be configured with locality bias as follows:

[ virtual-chassis locality-bias ]