CVE-2026-21912: MX10k Series: 'show system firmware' CLI command may lead to LC480 or LC2101 line card reset

A Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability in the method to collect FPC Ethernet firmware statistics of Juniper Networks Junos OS on MX10k Series allows a local, low-privileged attacker executing the 'show system firmware' CLI command to cause an LC480 or LC2101 line card to reset.

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 (MX10k Series) 0	21.2R3-S10 or later
Junos OS (MX10k Series) 21.4	21.4R3-S9 or later
Junos OS (MX10k Series) 22.2	22.2R3-S7 or later
Junos OS (MX10k Series) 22.4	22.4R3-S6 or later
Junos OS (MX10k Series) 23.2	23.2R2-S2 or later
Junos OS (MX10k Series) 23.4	23.4R2-S3 or later
Junos OS (MX10k Series) 24.2	24.2R2 or later

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

What it is

On MX10k Series systems with LC480 or LC2101 line cards, repeated execution of the 'show system firmware' CLI command can cause the line card to crash and restart. Additionally, some time after the line card crashes, chassisd may also crash and restart, generating a core dump.This issue affects Junos OS on MX10k Series:

all versions before 21.2R3-S10,
from 21.4 before 21.4R3-S9,
from 22.2 before 22.2R3-S7,
from 22.4 before 22.4R3-S6,
from 23.2 before 23.2R2-S2,
from 23.4 before 23.4R2-S3,
from 24.2 before 24.2R2.

Workarounds

Use CLI authorization to limit access to the 'show system firmware' command.

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.