dbcve.org
JunosOperating system · Juniper

CVE-2021-0236

MEDIUM · 6.5 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 →
71/100
Remediation priority · Elevated
Remotely reachable 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 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.

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

A vulnerability in the Routing Protocol Daemon (RPD) in Juniper Junos OS and Junos OS Evolved contains an improper check for unusual or exceptional conditions. When a specifically crafted BGP packet matches a particular flowspec configuration term in MP-BGP VPNv6 deployments, it triggers an RPD crash and restart, causing denial of service. Continued receipt of such packets creates a sustained DoS condition.

MitigationApply the vendor-supplied patches for affected versions (18.4R1-S8 or later for 18.4 branch, 19.1R2-S2 or later for 19.1, etc., and 20.3R2-EVO for Evolved). If VPNv6 FlowSpec is not required, consider disabling it as a temporary mitigation until patching is possible.

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:= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3
Junos Os EvolvedOperating system
Affected:= 19.1= 19.2= 19.3= 20.1

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

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. Identify Junos OS version
    Run 'show version' or 'request system version' to obtain the installed Junos version
    Affected if Version matches 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, or 20.3 (for standard Junos) or 19.1, 19.2, 19.3, or 20.1 (for Junos OS Evolved)
  2. Verify BGP VPNv6 configuration
    Run 'show configuration protocols bgp' and look for 'family inet-vpn unicast' or 'family inet6-vpn' configuration statements under the BGP group
    Affected if BGP is configured with IPv6 VPN address family (inet6-vpn) enabled
  3. Check for FlowSpec configuration in VPNv6
    Run 'show configuration routing-instances' and look for 'flow' term under protocols or policy-options, or check 'show configuration firewall flow'
    Affected if FlowSpec is configured within a VPNv6 routing instance
  4. Review RPD crash logs
    Run 'show system core-dumps' or check '/var/log/messages' for 'rpd' crash entries using 'show log messages | match rpd'
    Affected if RPD process has crashed or restarted unexpectedly
  5. Confirm MP-BGP VPNv6 flowspec traffic
    Monitor BGP peer sessions and check for 'show bgp neighbor' output for VPNv6 FlowSpec address family
    Affected if VPNv6 FlowSpec address family is advertised or received from BGP peers

Device is affected if it runs an affected Junos version, has BGP configured with VPNv6 FlowSpec, and is receiving specifically crafted BGP packets that match a flowspec term in MP-BGP VPNv6 deployments.

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

Apply the vendor-supplied patches for affected versions (18.4R1-S8 or later for 18.4 branch, 19.1R2-S2 or later for 19.1, etc., and 20.3R2-EVO for Evolved). If VPNv6 FlowSpec is not required, consider disabling it as a temporary mitigation until patching is possible.

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,600.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-0236 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2021-0236 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data