Junos Os EvolvedOperating system · Juniper

CVE-2021-0226

HIGH · 7.5 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 →

84/100

Remediation priority · High

Remotely reachable No privileges Zero-click

Official description

NVD · unedited

On Juniper Networks Junos OS Evolved devices, receipt of a specific IPv6 packet may cause an established IPv6 BGP session to terminate, creating a Denial of Service (DoS) condition. Continued receipt and processing of this packet will create a sustained Denial of Service (DoS) condition. This issue does not affect IPv4 BGP sessions. This issue affects IBGP or EBGP peer sessions with IPv6. This issue affects: Juniper Networks Junos OS Evolved: 19.4 versions prior to 19.4R2-S3-EVO; 20.1 versions prior to 20.1R2-S3-EVO; 20.2 versions prior to 20.2R2-S1-EVO; 20.3 versions prior to 20.3R2-EVO. This issue does not affect Juniper Networks Junos OS releases.

Technical summary

dbcve analysis · high confidence

A specific IPv6 packet can cause established IPv6 BGP sessions to terminate on Juniper Networks Junos OS Evolved devices, creating a sustained Denial of Service condition. The vulnerability affects IBGP and EBGP peer sessions using IPv6 transport, while IPv4 BGP sessions are unaffected.

MitigationUpgrade Junos OS Evolved to version 19.4R2-S3-EVO, 20.1R2-S3-EVO, 20.2R2-S1-EVO, 20.3R2-EVO or later. Consider implementing BGP session monitoring and filtering as an interim measure.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions

NVD · CPE data

Junos Os EvolvedOperating system

Affected:= 20.1= 20.2= 20.3

CVSS breakdown

From the vector

Attack vector: Network
Complexity: Low
Privileges: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

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

Am I affected?

dbcve checks

Work through these to decide whether this CVE applies to you.

Identify the device OS and version

Run 'show version' or 'system version' to confirm the device runs Junos OS Evolved and note the exact version number (e.g., 20.1, 20.2, 20.3)

Affected if The version matches exactly 20.1, 20.2, or 20.3 as listed in affected versions
Check for IPv6 BGP configuration

Run 'show configuration protocols bgp | display set' and look for 'family inet6' or 'family inet6-vpn' under the BGP group configuration

Affected if IPv6 address family is configured under any BGP group (indicates IPv6 BGP peers exist)
Verify active IPv6 BGP sessions

Run 'show bgp summary' and examine the 'Neighbour' column for IPv6 addresses, or run 'show bgp neighbor | match "Peer: "' to list all peer addresses

Affected if Any BGP neighbors use IPv6 addresses (fe80:, link-local, or global unicast) - these sessions are vulnerable to termination
Confirm IPv6 transport is in use for BGP

Run 'show bgp neighbor <ipv6-address>' and verify the 'Transport' or 'Local Interface' shows an IPv6 interface, or check 'show bgp summary' for IPv6 neighbor entries under the IPv6 unicast address family

Affected if BGP sessions are established over IPv6 transport - this is the exact condition the CVE exploits

A device is affected if it runs Junos OS Evolved versions 20.1, 20.2, or 20.3 AND has any active IPv6 BGP peer sessions (IBGP or EBGP), regardless of whether sessions are currently up or have recently terminated abnormally.

Generated from the published advisory. Verify against your own configuration.

Remediation

From vendor data

Mitigation available No clean upgrade yet — mitigate in the meantime

Mitigation

Upgrade Junos OS Evolved to version 19.4R2-S3-EVO, 20.1R2-S3-EVO, 20.2R2-S1-EVO, 20.3R2-EVO or later. Consider implementing BGP session monitoring and filtering as an interim measure.

Fix this in Junos Os Evolved Scoped from the published advisory

Consultation4.0 h
Implementation6.0 h
Testing4.0 h
Review / QA2.0 h

16.0 hours of engineering $2,840

Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,544.

Scan for this in your stack

Free · runs locally

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References

Primary sources

kb.juniper.netVendor Advisory
nvd.nist.govNVD record

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-0226 in production — separate from our analysis above.

Notes0 Guidelines

Know something about CVE-2021-0226?

The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.

The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon

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

At a glance

A fix existsA vendor remedy is published

Severity 7.5 High

Exploit likelihood EPSS, next 30 days 0.9%

Affects: Junos Os Evolved

Remediation

A high-priority fix

Fix this in Junos Os Evolved 16 hrs · Moderate

Typical engagement from $2,840

Get a fix See the full breakdown ↓

A high-priority vulnerability. Send your environment and a specialist will scope CVE-2021-0226 and return a fixed quote and timeline.

You’ll deal with our team directly and deploy the reviewed fix to staging first — never straight to production.

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.

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.

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.

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.

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.

Check your environment

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.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

No notes yet

Official description

Technical summary

Affected products & versions

CVSS breakdown

Am I affected?

Remediation

References