What is CVE-2021-31357?

CVE-2021-31357 is a high-severity vulnerability in Juniper Junos OS Evolved, classified under Command Injection. CVSS score: 7.8/10. Published 2021-10-19.

How severe is CVE-2021-31357?

High severity. CVSS v3 base score is 7.8 out of 10.

RCE in Juniper Junos OS Evolved

CVE-2021-31357

A command injection vulnerability in tcpdump command processing on Juniper Networks Junos OS Evolved allows an attacker with authenticated CLI access to be able to bypass configured access protections to execute arbitrary shell commands within the context of the current user. The vulnerability allows an attacker to bypass command authorization restrictions assigned to their specific user account and execute commands that are available to the privilege level for which the user is assigned. For example, a user that is in the super-user login class, but restricted to executing specific CLI commands could exploit the vulnerability to execute any other command available to an unrestricted admin user. This vulnerability does not increase the privilege level of the user, but rather bypasses any CLI command restrictions by allowing full access to the shell. This issue affects Juniper Networks Junos OS Evolved: All versions prior to 20.3R2-S1-EVO; 20.4 versions prior to 20.4R2-S2-EVO; 21.1 versions prior to 21.1R2-EVO; 21.2 versions prior to 21.2R1-S1-EVO, 21.2R2-EVO.

Vulnerability class: Command Injection (OS Command Injection)

Published 2021-10-19 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.006 (48.2th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 48th percentile — 48.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000

Affected products

Juniper Junos OS Evolved — versions 20.4, 21.1, 21.2
Juniper Networks Junos OS Evolved — versions unspecified, 20.4, 21.1

Weakness classification (CWE)

References

kb.juniper.net/JSA11221 (Vendor Advisory)

Frequently asked questions

What is CVE-2021-31357?: CVE-2021-31357 is a high-severity vulnerability in Juniper Junos OS Evolved, classified under Command Injection. CVSS score: 7.8/10. Published 2021-10-19.
How severe is CVE-2021-31357?: High severity. CVSS v3 base score is 7.8 out of 10.