CVE-2026-0203: Receipt of a specifically malformed ICMP packet causes an FPC restart

An Improper Handling of Exceptional Conditions vulnerability in packet processing of Juniper Networks Junos OS allows an unauthenticated, network-adjacent attacker sending a specifically malformed ICMP packet to cause an FPC to crash and restart, resulting in a Denial of Service (DoS).

Published 14 Jan 2026

Automatic summary from the vendor's CVE record. We haven't written a full analysis of this vulnerability yet.

Affected and fixed versions

Product / branch	Fixed in
Junos OS 0	21.2R3-S9 or later
Junos OS 21.4	21.4R3-S10 or later
Junos OS 22.2	22.2R3-S7 or later
Junos OS 22.3	22.3R3-S4 or later
Junos OS 22.4	22.4R3-S5 or later
Junos OS 23.2	23.2R2-S3 or later
Junos OS 23.4	23.4R2-S3 or later
Junos OS 24.2	24.2R1-S2, 24.2R2 or later

Always confirm against the vendor advisory, which lists every fixed hotfix.

What it is

When an ICMP packet is received with a specifically malformed IP header value, the FPC receiving the packet crashes and restarts. Due to the specific type of malformed packet, adjacent upstream routers would not forward the packet, limiting the attack surface to adjacent networks.

This issue only affects ICMPv4. ICMPv6 is not vulnerable to this issue.

This issue does not affect AFT-based line cards such as the MPC10, MPC11, LC4800, LC9600, and MX304.

This issue affects Junos OS:

all versions before 21.2R3-S9,
from 21.4 before 21.4R3-S10,
from 22.2 before 22.2R3-S7,
from 22.3 before 22.3R3-S4,
from 22.4 before 22.4R3-S5,
from 23.2 before 23.2R2-S3,
from 23.4 before 23.4R2-S3,
from 24.2 before 24.2R1-S2, 24.2R2.

Workarounds

There are no known workarounds for this issue.

Exploitation

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

KEV status, EPSS score and vendor data refreshed automatically, last on 13 Oct 2026.