Vulnerability in Juniper Junos

CVE-2026-21912

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.

Vulnerability class: TOCTOU (Time-of-Check to Time-of-Use)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.001 (1.3th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 1st percentile — 1.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-21912: held from 0.001 to 0.001.

EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: +0.000

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-21912?
CVE-2026-21912 is a medium-severity vulnerability in Juniper Junos, classified under Time-of-check Time-of-use (TOCTOU) Race Condition. CVSS score: 5.5/10. Published 2026-01-15.
How severe is CVE-2026-21912?
Medium severity. CVSS v3 base score is 5.5 out of 10.