LiveActive security incident?Get immediate response
CVE Record

CVE-2021-0236: Junos OS: A specific BGP VPNv6 flowspec message causes routing protocol daemon (rpd) process to crash with a core.

Due to an improper check for unusual or exceptional conditions in Juniper Networks Junos OS and Junos OS Evolved the Routing Protocol Daemon (RPD) service, upon receipt of a specific matching BGP packet meeting a specific term in the flowspec configuration, crashes and restarts causing a Denial of Service (DoS). Continued receipt and processing of this packet will create a sustained Denial of Service (DoS) condition. This issue affects only Multiprotocol BGP (MP-BGP) VPNv6 FlowSpec deployments. This issue affects: Juniper Networks Junos OS: 18.4 versions prior to 18.4R1-S8, 18.4R2-S7, 18.4R3-S7; 19.1 versions prior to 19.1R2-S2, 19.1R3-S4; 19.2 versions prior to 19.2R1-S6, 19.2R3-S2; 19.3 versions prior to 19.3R3-S2; 19.4 versions prior to 19.4R2-S4, 19.4R3-S1; 20.1 versions prior to 20.1R2, 20.1R3; 20.2 versions prior to 20.2R2, 20.2R3; 20.3 versions prior to 20.3R1-S1, 20.3R2. Juniper Networks Junos OS Evolved: All versions after 18.4R1-EVO prior to 20.3R2-EVO. This issue does not affect: Juniper Networks Junos OS versions prior to 18.4R1. Juniper Networks Junos OS Evolved versions prior to 18.4R1-EVO.

MediumCVSS 6.5Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-0236 is a denial-of-service issue in Juniper Junos routing software. In specific MP-BGP VPNv6 FlowSpec deployments, a crafted or unusual BGP packet can crash and restart the routing protocol daemon, potentially disrupting routing repeatedly if the packet continues arriving.

Executive priority

Treat this as a focused network availability risk, not a broad enterprise compromise issue. Prioritize remediation where affected Juniper routers support critical routing domains or customer-facing connectivity, especially if MP-BGP VPNv6 FlowSpec is enabled.

Technical view

The flaw is an improper exceptional-condition check in Junos OS and Junos OS Evolved RPD. Receipt of a specific BGP VPNv6 FlowSpec packet matching a configured FlowSpec term can crash RPD and generate a core, causing availability impact. CVSS is 6.5 with network attack vector and low complexity, but low privileges are required.

Likely exposure

Exposure appears limited to Juniper Networks Junos OS or Junos OS Evolved devices running affected versions and using MP-BGP VPNv6 FlowSpec. Junos versions before 18.4R1 and Junos OS Evolved before 18.4R1-EVO are stated as unaffected.

Exploitation context

The provided sources do not show CISA KEV listing or confirmed active exploitation. The vulnerability is network-reachable in the affected BGP context, but the source bundle does not provide exploit details, public exploit status, or broader abuse evidence.

Researcher notes

Scope is narrow but operationally important. The key exposure condition is MP-BGP VPNv6 FlowSpec plus affected Junos release. Sources identify CWE-754 and availability-only impact; they do not support claims about data compromise, unauthenticated exploitation, or active exploitation.

Mitigation direction

  • Upgrade affected Junos OS devices to the fixed release trains listed by Juniper.
  • Upgrade affected Junos OS Evolved devices to 20.3R2-EVO or later supported fixed guidance.
  • Use Juniper JSA11131 as the authoritative remediation source for exact target versions.
  • Review whether MP-BGP VPNv6 FlowSpec is required before making compensating configuration changes.
  • Monitor affected routers for repeated RPD crashes until remediation is complete.

Validation and detection

  • Inventory Juniper devices running Junos OS or Junos OS Evolved.
  • Confirm whether MP-BGP VPNv6 FlowSpec is configured and in use.
  • Compare installed versions against the affected and fixed releases in JSA11131.
  • Check logs and core files for RPD crash or restart patterns.
  • Verify post-upgrade versions match Juniper fixed release guidance.
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

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-754: 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-2021-0236 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
6.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/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
6.5CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H2.83.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.5Medium
CVSS 3.1 vector shape for CVE-2021-0236Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/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, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3Listed
Juniper NetworksJunos OS Evolvedunspecified, 20.3-EVOListed
Weakness

CWE details

CWE-754

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

CWE-754 · source CWE mapping

Improper Check for Unusual or Exceptional Conditions

Improper Check for Unusual or Exceptional Conditions represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs