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CVE Record

CVE-2021-0293: Junos OS: Out-of-memory condition and crashes can occur after executing a certain CLI command repeatedly

A vulnerability in Juniper Networks Junos OS caused by Missing Release of Memory after Effective Lifetime leads to a memory leak each time the CLI command 'show system connections extensive' is executed. The amount of memory leaked on each execution depends on the number of TCP connections from and to the system. Repeated execution will cause more memory to leak and eventually daemons that need to allocate additionally memory and ultimately the kernel to crash, which will result in traffic loss. Continued execution of this command will cause a sustained Denial of Service (DoS) condition. An administrator can use the following CLI command to monitor for increase in memory consumption of the netstat process, if it exists: user@junos> show system processes extensive | match "username|netstat" PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND 21181 root 100 0 5458M 4913M CPU3 2 0:59 97.27% netstat The following log message might be observed if this issue happens: kernel: %KERN-3: pid 21181 (netstat), uid 0, was killed: out of swap space This issue affects Juniper Networks Junos OS 18.2 versions prior to 18.2R2-S8, 18.2R3-S7. 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S6, 18.4R3-S7; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3-S4; 19.2 versions prior to 19.2R1-S6, 19.2R3-S2; 19.3 versions prior to 19.3R2-S6, 19.3R3-S1; 19.4 versions prior to 19.4R1-S4, 19.4R2-S3, 19.4R3-S1; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R2-S1, 20.2R3; 20.3 versions prior to 20.3R1-S1, 20.3R2; This issue does not affect Juniper Networks Junos OS versions prior to 18.2R1.

MediumCVSS 5.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Affected Juniper Junos OS devices can lose availability when a permitted local user repeatedly runs a specific diagnostic CLI command. Each run leaks memory, eventually crashing daemons or the kernel and causing traffic loss. The supplied sources do not show active exploitation, but the impact matters for critical network devices.

Executive priority

Treat this as a moderate availability risk. It is not presented as remote or actively exploited, but affected network infrastructure can lose traffic if an authorized CLI user triggers the condition repeatedly.

Technical view

CVE-2021-0293 is a CWE-401 memory leak in Junos OS triggered by repeated use of the affected CLI behavior. Leak size depends on TCP connection volume. Over time, the netstat process, daemons, and ultimately the kernel can run out of memory, producing sustained DoS. CVSS is 5.5, local, low-privilege, availability-high.

Likely exposure

Exposure is limited to Juniper Networks Junos OS 18.2 through 20.3 releases listed as affected, before the fixed release trains named by Juniper. Junos OS before 18.2R1 is stated as not affected.

Exploitation context

The provided evidence describes local authenticated exploitation requiring CLI access and repeated command execution. CISA KEV status is false in the bundle, and no supplied source claims active exploitation in the wild.

Researcher notes

Key constraints are local access and repeat execution. Validation should focus on version exposure, administrator access paths, memory-growth telemetry, and kernel out-of-swap logs. The source bundle does not provide exploit prevalence or additional mitigations beyond fixed releases and monitoring indicators.

Mitigation direction

  • Upgrade affected Junos OS devices to Juniper's fixed releases or later.
  • Prioritize internet-edge and core routing devices where traffic loss has high business impact.
  • Restrict CLI access to trusted administrators and review low-privilege operational roles.
  • Monitor vendor guidance for platform-specific upgrade paths or compensating controls.

Validation and detection

  • Inventory Junos OS versions and compare them with Juniper's affected and fixed release lists.
  • Check whether devices run affected 18.2 through 20.3 release trains.
  • Review logs for netstat out-of-memory or out-of-swap messages described by Juniper.
  • Monitor memory consumption patterns on devices where remediation is pending.
Prepared
Confidence
high
Sources
3

Public sources used

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

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ATT&CK lookup starting points

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cwe · low confidence lookup

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cve · low confidence lookup

CVE-2021-0293 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.5 (3.1)
Known Exploited
No
Published

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

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
5.5CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

5.5Medium
CVSS 3.1 vector shape for CVE-2021-0293Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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 OSunspecified, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3, 18.2Listed
Weakness

CWE details

CWE-401

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

CWE-401 · source CWE mapping

Missing Release of Memory after Effective Lifetime

Missing Release of Memory after Effective Lifetime represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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