Junos OS: EX Series: Subscribing to an unsupported telemetry sensor path causes fxpc process crash

An Improper Handling of Undefined Parameters vulnerability in the packet forwarding engine (pfe) of Juniper Networks Junos OS on EX Series devices allows an authenticated attacker with low privileges to cause a Denial-of-Service (DoS).

If an attempt is made to subscribe to an unsupported telemetry sensor path on EX2300, EX3400, EX4000, EX4100 and EX4400 via gRPC, this causes the FPC to crash. This leads to a complete service outage until the module has automatically restarted. 

The following log message can be seen when this issue happens:

agentd[<PID>]: AGENTD_RESOURCE_NOT_FOUND: No resource name found for <sensor>

This issue affects Junos OS on

EX2300, EX3400, EX4000, EX4100 and EX4400

devices:

* all versions before 23.2R2-S7,
* 23.4 versions before 23.4R2-S8,
* 24.2 versions before 24.2R2-S5,
* 24.4 versions before 24.4R2.