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JunosOperating system · Juniper

CVE-2021-31377

MEDIUM · 5.5 CVSS v3.1 Published 2021-10-19
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
57/100
Remediation priority · Elevated
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
An Incorrect Permission Assignment for Critical Resource vulnerability of a certain file in the filesystem of Junos OS allows a local authenticated attacker to cause routing process daemon (RPD) to crash and restart, causing a Denial of Service (DoS). Repeated actions by the attacker will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS: 15.1 versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R2-S13, 17.4R3-S5; 18.1 versions prior to 18.1R3-S13; 18.2 versions prior to 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R2-S8, 18.4R3-S7; 19.1 versions prior to 19.1R2-S3, 19.1R3-S5; 19.2 versions prior to 19.2R3-S2; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R2-S4, 19.4R3-S2; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R2-S3, 20.2R3; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R1-S1, 20.4R2.

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 local privilege escalation vulnerability in Junos OS where a specific file in the filesystem has incorrect permissions, allowing an authenticated local attacker to modify or interact with it in a way that causes the routing process daemon (RPD) to crash and restart, resulting in denial of service.

MitigationApply the vendor-supplied Junos OS updates for the affected versions to correct the file permissions, or implement network access controls to limit local access to trusted administrators only.

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
JunosOperating system
Affected:= 15.1= 17.3= 17.4= 18.1= 18.2= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1

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
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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. Identify Junos OS version
    Run 'show version' or 'show version detail' via CLI to display the installed Junos OS version
    Affected if The displayed version matches any of these: 15.1, 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, or 20.1
  2. Confirm local authenticated access exists
    Verify whether untrusted local user accounts or shared administrator accounts exist on the system with CLI login privileges
    Affected if Untrusted or unauthorized accounts have authenticated access to the Junos CLI or shell
  3. Inspect permissions on the vulnerable file
    Use 'ls -la' or 'file permissions' command on the filesystem path identified in Junos security advisories for this CVE to check owner and permission bits
    Affected if The file is writable by non-privileged users or has mode 666 or similar overly permissive settings
  4. Monitor RPD daemon stability
    Check 'show system processes' or review system logs for repeated RPD crash events and restart cycles
    Affected if The routing process daemon (RPD) is crashing and restarting frequently, which may indicate exploitation of this vulnerability

You are affected if your Junos OS version is 15.1, 17.3-17.4, 18.1-18.4, 19.1-19.4, or 20.1 AND untrusted local users have authenticated CLI access AND the vulnerable file has permissive incorrect permissions.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the vendor-supplied Junos OS updates for the affected versions to correct the file permissions, or implement network access controls to limit local access to trusted administrators only.

Recommended fix High confidence

Upgrade to the fixed version for your branch: 15.1R7-S9, 17.3R3-S12, 17.4R2-S13/17.4R3-S5, 18.1R3-S13, 18.2R3-S8, 18.3R3-S5, 18.4R2-S8/18.4R3-S7, 19.1R2-S3/19.1R3-S5, 19.2R3-S2, 19.3R2-S6/19.3R3-S2, 19.4R1-S4/19.4R2-S4/19.4R3-S2, 20.1R2-S2/20.1R3, 20.2R2-S3/20.2R3, 20.3R3, or 20.4R1-S1/20.4R2

  1. 1. Identify the current Junos OS version running on the device using 'show version' command
  2. 2. Determine which branch version you are on (15.1, 17.3, 17.4, 18.1, etc.) from the output
  3. 3. Navigate to the Juniper security advisories page at kb.juniper.net to obtain the specific upgrade package for your branch
  4. 4. Download the appropriate fixed release for your version branch (e.g., 15.1R7-S9, 17.3R3-S12, 17.4R2-S13, 18.1R3-S13, etc.)
  5. 5. Transfer the Junos upgrade package to the device using SCP or FTP
  6. 6. Run 'request system software add <package-name>' to install the upgrade
  7. 7. Reboot the device using 'request system reboot' to complete the installation
  8. 8. After reboot, verify the new version is installed using 'show version' and confirm it matches the fixed release
Caveat Standard Junos upgrade caveats apply - review release notes for compatibility and ensure configuration backup before upgrading

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

Fix this in Junos Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,570
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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-2021-31377 in production — separate from our analysis above.

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What this is

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