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

Medium 6.8 Published 15 Jan 2026 Updated 15 Jan 2026

A local low-privileged attacker can cause line card and chassis daemon crashes by repeatedly executing a specific CLI command due to a race condition.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-21912?

CVE-2026-21912 is a medium-severity vulnerability in Juniper Junos, published on 15 Jan 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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.

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.

Weakness: CWE-367

Which versions are affected by CVE-2026-21912?

It affects 1 product.

Products include Juniper Junos.

How do I fix CVE-2026-21912?

No fix has been published for CVE-2026-21912 yet. Limit exposure of the affected software until one is available.

Is CVE-2026-21912 being exploited?

There is no known exploitation of CVE-2026-21912 in the wild and no public exploit code.

All Juniper Junos vulnerabilities

Sources

Also known as GHSA-w5q5-7f2p-x4hm.