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CVE Record

CVE-2021-0258: Junos OS: Kernel panic upon receipt of specific TCPv6 packet on management interface

A vulnerability in the forwarding of transit TCPv6 packets received on the Ethernet management interface of Juniper Networks Junos OS allows an attacker to trigger a kernel panic, leading to a Denial of Service (DoS). Continued receipt and processing of these transit packets will create a sustained Denial of Service (DoS) condition. This issue only occurs when TCPv6 packets are routed through the management interface. Other transit traffic, and traffic destined to the management interface, are unaffected by this vulnerability. This issue was introduced as part of a TCP Parallelization feature added in Junos OS 17.2, and affects systems with concurrent network stack enabled. This feature is enabled by default, but can be disabled (see WORKAROUND section below). This issue affects Juniper Networks Junos OS: 17.2 versions prior to 17.2R3-S4; 17.3 versions prior to 17.3R3-S9; 17.4 versions prior to 17.4R2-S11, 17.4R3-S2; 18.1 versions prior to 18.1R3-S11; 18.2 versions prior to 18.2R3-S5; 18.3 versions prior to 18.3R2-S4, 18.3R3-S3; 18.4 versions prior to 18.4R2-S5, 18.4R3-S4; 19.1 versions prior to 19.1R2-S2, 19.1R3; 19.2 versions prior to 19.2R1-S5, 19.2R2; 19.3 versions prior to 19.3R2-S4, 19.3R3; 19.4 versions prior to 19.4R1-S3, 19.4R2. This issue does not affect Juniper Networks Junos OS versions prior to 17.2R1.

MediumCVSS 5.9Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Certain Juniper Junos OS devices can crash if they route specific TCP over IPv6 traffic through the Ethernet management interface. This is an availability issue: repeated traffic can keep the device in a denial-of-service condition. The risk is most relevant where management interfaces can forward transit IPv6 traffic.

Executive priority

Treat as a targeted availability risk. Patch during the next approved network maintenance window, sooner for critical devices whose management interfaces can route IPv6 transit traffic.

Technical view

CVE-2021-0258 is a Junos OS kernel panic condition tied to transit TCPv6 forwarding on the Ethernet management interface with the concurrent network stack enabled. Traffic destined to the management interface and other transit traffic are reported unaffected. The issue was introduced with TCP Parallelization in Junos OS 17.2.

Likely exposure

Exposure is limited to affected Junos OS 17.2 through 19.4 releases before the fixed branch versions, on systems where TCPv6 packets can be routed through the management interface.

Exploitation context

The CVE has network attack vector and requires no privileges or user interaction, but attack complexity is high. The source bundle does not show KEV listing or active exploitation evidence.

Researcher notes

Key boundary conditions matter: only TCPv6 transit through the management interface is in scope. Other transit traffic and traffic addressed to the management interface are described as unaffected. Evidence is insufficient to claim exploitation in the wild.

Mitigation direction

  • Upgrade affected Junos OS branches to the fixed versions listed by Juniper.
  • Prevent transit TCPv6 routing through Ethernet management interfaces where feasible.
  • Review Juniper JSA11149 for the supported workaround involving concurrent network stack disabling.
  • Prioritize devices where management interfaces are reachable from untrusted or broad internal networks.

Validation and detection

  • Inventory Junos OS versions across Juniper devices.
  • Identify devices running affected 17.2 through 19.4 branch versions.
  • Confirm whether Ethernet management interfaces route transit IPv6 TCP traffic.
  • Check whether the concurrent network stack feature is enabled.
  • Review device history for unexplained kernel panics or availability drops.
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

CWE-362: Exact CWE lookup

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cve · low confidence lookup

CVE-2021-0258 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.9 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:H/PR:N/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
5.9CVSS 3.1MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H2.23.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

5.9Medium
CVSS 3.1 vector shape for CVE-2021-0258Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:H/PR:N/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 OS17.2, 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4Listed
Weakness

CWE details

CWE-362

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

CWE-362 · source CWE mapping

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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