CVE-2024-39542: A malformed CFM packet or specific transit traffic leads to FPC crash

What it is

An Improper Validation of Syntactic Correctness of Input vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on MX Series with MPC10/11 or LC9600, MX304, and Junos OS Evolved on ACX Series and PTX Series allows an unauthenticated, network based attacker to cause a Denial-of-Service (DoS).

This issue can occur in two scenarios:

1. If a device, which is configured with SFLOW and ECMP, receives specific valid transit traffic, which is subject to sampling, the packetio process crashes, which in turn leads to an evo-aftman crash and causes the FPC to stop working until it is restarted. (This scenario is only applicable to PTX but not to ACX or MX.)

1. If a device receives a malformed CFM packet on an interface configured with CFM, the packetio process crashes, which in turn leads to an evo-aftman crash and causes the FPC to stop working until it is restarted. Please note that the CVSS score is for the formally more severe issue 1.

The CVSS score for scenario 2. is: 6.5 (CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

This issue affects Junos OS:

• All versions before 21.2R3-S4,
• 21.4 versions before 21.4R2,
• 22.2 versions before 22.2R3-S2;

Junos OS Evolved:

• All versions before 21.2R3-S8-EVO,
• 21.4 versions before 21.4R2-EVO.

Am I affected?

To be exposed to this issue at least one of CFM or sampling needs to be configured:

1. CFM:

[  protocols oam ethernet connectivity-fault-management maintenance-domain <md_name> maintenance-association <ma_name> mep <number> interface <interface> ] OR [  protocols oam ethernet connectivity-fault-management maintenance-domain <md_name> interface <interface> / vlan <vlan> ]

1. ECMP, sampling

[

protocols sflow interfaces <interface>

]

Workarounds

There are no known workarounds for this issue.

Exploitation

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.