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JunosOperating system · Juniper

CVE-2021-31368

HIGH · 7.5 CVSS v3.1 Published 2021-10-19
Fix available
A fix is available. Upgrade to 18.1 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges 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 Uncontrolled Resource Consumption vulnerability in the kernel of Juniper Networks JUNOS OS allows an unauthenticated network based attacker to cause 100% CPU load and the device to become unresponsive by sending a flood of traffic to the out-of-band management ethernet port. Continued receipted of a flood will create a sustained Denial of Service (DoS) condition. Once the flood subsides the system will recover by itself. An indication that the system is affected by this issue would be that kernel and netisr process are shown to be using a lot of CPU cycles like in the following example output: user@host> show system processes extensive ... PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND 16 root -72 - 0K 304K WAIT 1 839:40 88.96% intr{swi1: netisr 0} 0 root 97 - 0K 160K RUN 1 732:43 87.99% kernel{bcm560xgmac0 que} This issue affects Juniper Networks JUNOS OS on EX2300 Series, EX3400 Series, and ACX710: All 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-S9; 19.1 versions prior to 19.1R3-S5; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R3; 20.3 versions prior to 20.3R2-S1, 20.3R3; 20.4 versions prior to 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

Uncontrolled resource consumption vulnerability in the JUNOS OS kernel allows an unauthenticated remote attacker to cause 100% CPU utilization by flooding traffic to the out-of-band management ethernet port, rendering the device unresponsive. The kernel and netisr processes consume excessive CPU cycles during the attack, creating a sustained denial-of-service condition that self-recovers once traffic subsides.

MitigationApply the appropriate JUNOS OS software patch from the vendor advisory to the affected devices (EX2300, EX3400, ACX710 series). Alternatively, implement network filtering or access control lists to restrict and limit traffic reaching the out-of-band management interface.

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:< 18.1= 18.1= 18.2= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/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. Confirm device model
    Run 'show chassis hardware' or 'show version' command to identify the exact device model
    Affected if Device is an EX2300, EX3400, or ACX710 series

Device is vulnerable if it is an EX2300, EX3400, or ACX710 running Junos OS versions 18.1-20.3 or below 18.1, with an active out-of-band management interface that could be flooded with traffic

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 18.1 or later
Fixed in 18.1
Interim mitigation

Apply the appropriate JUNOS OS software patch from the vendor advisory to the affected devices (EX2300, EX3400, ACX710 series). Alternatively, implement network filtering or access control lists to restrict and limit traffic reaching the out-of-band management interface.

Recommended fix High confidence

Upgrade to 18.1R3-S13 (or later), 18.2R3-S8 (or later), or 18.3R3-S5 (or later) depending on your current branch; Juniper recommends moving to the most recent stable release available for your hardware platform

  1. 1. Identify the current Junos OS version running on the device using 'show version'
  2. 2. Determine the appropriate fixed release based on your current version branch from the vulnerability advisory
  3. 3. Download the recommended Junos OS service release from the Juniper Networks support portal (requires valid service contract)
  4. 4. Transfer the Junos OS upgrade package to the device using the out-of-band management interface or internal flash
  5. 5. Verify the MD5/SHA256 checksum of the uploaded package against the published checksum
  6. 6. Initiate the software upgrade using 'request system software add <package-name>'
  7. 7. Reboot the device using 'request system reboot' to apply the new software
  8. 8. After reboot, verify the new version is installed using 'show version'
Caveat Review Juniper release notes for any configuration changes or deprecated features between versions; some features may behave differently in newer releases

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

Fix this in Junos Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,800
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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-2021-31368 in production — separate from our analysis above.

No notes yet

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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