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JunosOperating system · Juniper

CVE-2021-0234

MEDIUM · 5.8 CVSS v3.1 Published 2021-04-22
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
67/100
Remediation priority · Elevated
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
Due to an improper Initialization vulnerability on Juniper Networks Junos OS QFX5100-96S devices with QFX 5e Series image installed, ddos-protection configuration changes will not take effect beyond the default DDoS (Distributed Denial of Service) settings when configured from the CLI. The DDoS protection (jddosd) daemon allows the device to continue to function while protecting the packet forwarding engine (PFE) during the DDoS attack. When this issue occurs, the default DDoS settings within the PFE apply, as CPU bound packets will be throttled and dropped in the PFE when the limits are exceeded. To check if the device has this issue, the administrator can execute the following command to monitor the status of DDoS protection: user@device> show ddos-protection protocols error: the ddos-protection subsystem is not running This issue affects only QFX5100-96S devices. No other products or platforms are affected by this issue. This issue affects: Juniper Networks Junos OS on QFX5100-96S: 17.3 versions prior to 17.3R3-S10; 17.4 versions prior to 17.4R3-S4; 18.1 versions prior to 18.1R3-S10; 18.2 versions prior to 18.2R3-S3; 18.3 versions prior to 18.3R3-S2; 18.4 versions prior to 18.4R2-S4, 18.4R3-S1; 19.1 versions prior to 19.1R3, 19.1R3-S4; 19.2 versions prior to 19.2R2; 19.3 versions prior to 19.3R3; 19.4 versions prior to 19.4R2;

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

An improper initialization vulnerability in Juniper Networks Junos OS on QFX5100-96S devices causes ddos-protection configuration changes to not take effect beyond default DDoS settings. The jddosd daemon fails to properly initialize, causing the device to fall back to PFE default settings where CPU-bound packets are throttled and dropped when limits are exceeded. The error message 'the ddos-protection subsystem is not running' confirms the subsystem failure.

MitigationUpgrade Junos OS on QFX5100-96S devices to the fixed versions specified (17.3R3-S10, 17.4R3-S4, 18.1R3-S10, 18.2R3-S3, 18.3R3-S2, 18.4R2-S4/18.4R3-S1, 19.1R3/19.1R3-S4, 19.2R2, 19.3R3, or 19.4R2 or later) to remediate this vulnerability.

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:= 17.3= 17.4= 18.1= 18.2= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4

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
Changed
Confidentiality
None
Integrity
None
Availability
Low

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

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. Verify device model is QFX5100-96S
    Run 'show chassis hardware' or 'show version' to confirm the device is a QFX5100-96S model. This vulnerability only affects this specific hardware platform.
    Affected if Device is not a QFX5100-96S - the vulnerability is specific to this model.
  2. Check Junos OS version
    Run 'show version' to obtain the installed Junos OS version and compare it against the affected versions: 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, or 19.4.
    Affected if Installed version matches one of the affected versions listed.
  3. Verify ddos-protection configuration is non-default
    Run 'show configuration ddos-protection' to view the current DDoS protection settings. Check if any protocol or packet type has custom (non-default) configuration applied.
    Affected if Custom ddos-protection configuration exists but is not taking effect as expected.
  4. Search for error message in system logs
    Run 'show log messages | match ddos-protection' or check system logs for the exact string 'the ddos-protection subsystem is not running'. This message confirms the jddosd daemon failed to initialize.
    Affected if The error message 'the ddos-protection subsystem is not running' appears in logs.
  5. Check jddosd daemon status
    Run 'show system processes' or 'show ddos-protection' to verify if the jddosd daemon is running and the DDoS protection subsystem is operational.
    Affected if The jddosd daemon is not running or the subsystem reports as unavailable.

A defender is affected if they are running any of the listed Junos versions on a QFX5100-96S device, have custom ddos-protection configuration, and observe either the specific error message or daemon failure.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Junos OS on QFX5100-96S devices to the fixed versions specified (17.3R3-S10, 17.4R3-S4, 18.1R3-S10, 18.2R3-S3, 18.3R3-S2, 18.4R2-S4/18.4R3-S1, 19.1R3/19.1R3-S4, 19.2R2, 19.3R3, or 19.4R2 or later) to remediate this vulnerability.

Fix this in Junos Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2021-0234 in production — separate from our analysis above.

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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
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