dbcve.org
Junos Os EvolvedOperating system · Juniper

CVE-2021-31358

HIGH · 7.8 CVSS v3.1 Published 2021-10-19
Fix available
A fix is available. Upgrade to after 20.3 or later.
See remediation →
80/100
Remediation priority · High
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A command injection vulnerability in sftp 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 20.4R2-S2-EVO; 21.1 versions prior to 21.1R2-EVO; 21.2 versions prior to 21.2R1-S1-EVO, 21.2R2-EVO.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This is a command injection vulnerability in the sftp command processing component of Juniper Networks Junos OS Evolved. An authenticated attacker with CLI access can bypass configured command authorization restrictions and execute arbitrary shell commands within the context of the current user. The vulnerability does not elevate privileges but allows restricted users to access the full shell.

MitigationUpgrade to a fixed version (20.4R2-S2-EVO, 21.1R2-EVO, 21.2R1-S1-EVO, 21.2R2-EVO or later) or implement strict access control and monitor for unauthorized shell access.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Junos Os EvolvedOperating system
Affected:<= 20.3= 20.4= 21.1= 21.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm Junos OS Evolved is in use
    Run 'show system version' or 'show version' and look for 'Junos OS Evolved' in the output. This vulnerability only affects Junos OS Evolved, not standard Junos OS.
    Affected if The device is running Junos OS Evolved (not standard Junos OS)
  2. Identify the installed version
    Run 'show version evo' to display the exact Junos OS Evolved version number. Compare this version against the affected ranges: any version <= 20.3, or exactly 20.4, 21.1, or 21.2.
    Affected if The installed version is 20.3 or earlier, or exactly 20.4, 21.1, or 21.2
  3. Verify restricted CLI user accounts exist
    Run 'show configuration system login' and look for user accounts with 'class' assignments other than 'super-user' or 'root'. Check for users assigned to restricted classes like 'operator', 'read-only', or custom classes.
    Affected if There are non-super-user accounts configured with CLI access
  4. Confirm command authorization is configured
    Run 'show configuration system login class' to review authorization permissions. Look for configurations that restrict which commands users can execute.
    Affected if Command authorization restrictions are defined in login classes
  5. Inspect for shell access attempts
    Review system logs via 'show log messages' or 'show system statistics' for entries indicating shell (shell) access by non-privileged accounts. Search for patterns like 'user X started shell' or 'cli started by user X'.
    Affected if Shell access is observed for accounts that should not have shell privileges

You are affected if the device runs Junos OS Evolved in versions 20.3 or earlier, or exactly 20.4/21.1/21.2, and there are restricted CLI users who could bypass their authorization to access the shell via sftp.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 20.3
Interim mitigation

Upgrade to a fixed version (20.4R2-S2-EVO, 21.1R2-EVO, 21.2R1-S1-EVO, 21.2R2-EVO or later) or implement strict access control and monitor for unauthorized shell access.

Recommended fix High confidence

21.2R2-EVO or later (or 20.4R2-S2-EVO / 21.1R2-EVO depending on compatibility needs)

  1. Identify the current Junos OS Evolved version using 'show version' command
  2. Review the current configuration backup to ensure it's up-to-date
  3. Schedule a maintenance window for the upgrade process
  4. Download the fixed release image (20.4R2-S2-EVO, 21.1R2-EVO, 21.2R1-S1-EVO, or 21.2R2-EVO or later) from the Juniper Networks download portal
  5. Upload the software package to the device using 'request system software add' command
  6. Reboot the device to complete the installation using 'request system reboot' command
  7. After reboot, verify the new version is installed using 'show version'
  8. Verify the sftp command now properly sanitizes input and enforces command restrictions
Caveat Standard Junos OS upgrade considerations apply - review release notes for any behavior changes between your current version and the target version

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Os Evolved Scoped from the published advisory
  • Consultation8.0 h
  • Implementation4.0 h
  • Testing8.0 h
  • Review / QA4.0 h
24.0 hours of engineering $4,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,784.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-31358 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-31358 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data