LiveActive security incident?Get immediate response
CVE Record

CVE-2021-0234: Junos OS: QFX5100-96S: DDoS protection does not work as expected.

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;

MediumCVSS 5.8Not KEV-listedUpdated
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Some Juniper QFX5100-96S switches may silently ignore customized DDoS protection settings. Default protection still applies, but operators expecting tuned thresholds could have less availability protection during attack traffic than planned.

Executive priority

Treat as a targeted platform hygiene issue, not a broad emergency. Prioritize remediation where QFX5100-96S devices support critical services or depend on tuned DDoS controls.

Technical view

CVE-2021-0234 is an improper initialization issue in Junos OS on QFX5100-96S with the QFX 5e Series image. CLI ddos-protection changes do not take effect beyond defaults because the jddosd subsystem may not run as expected.

Likely exposure

Exposure is narrow: only Juniper Networks Junos OS on QFX5100-96S in the listed 17.3 through 19.4 release trains before fixed releases. The advisory states no other products or platforms are affected.

Exploitation context

The provided sources do not indicate active exploitation, and the CVE is not listed as KEV. Risk is availability-focused: custom DDoS protection may not be enforced during attack conditions.

Researcher notes

The key observable is failure of the ddos-protection subsystem status check. Evidence supports reduced effectiveness of customized protection, while default PFE throttling still applies. No exploit details are provided in the bundle.

Mitigation direction

  • Identify QFX5100-96S devices running the QFX 5e Series image.
  • Upgrade affected Junos OS releases to Juniper-listed fixed versions.
  • Check Juniper JSA11129 for current vendor guidance before maintenance.
  • Do not rely on customized ddos-protection settings until validated.
  • Prioritize internet-facing or high-criticality switching environments.

Validation and detection

  • Inventory QFX5100-96S devices and compare Junos versions against affected ranges.
  • Run the vendor-provided DDoS protection status check.
  • Investigate devices returning that the ddos-protection subsystem is not running.
  • After upgrade, confirm ddos-protection status and intended configuration behavior.
Prepared
Confidence
high
Sources
3

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-665: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2021-0234 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.8 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
5.8CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L3.91.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

5.8Medium
CVSS 3.1 vector shape for CVE-2021-0234Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Juniper NetworksJunos OS17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4Listed
Weakness

CWE details

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-665 · source CWE mapping

Improper Initialization

Improper Initialization represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.