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JunosOperating system · Juniper

CVE-2021-0299

HIGH · 7.5 CVSS v3.1 Published 2021-10-19
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 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
An Improper Handling of Exceptional Conditions vulnerability in the processing of a transit or directly received malformed IPv6 packet in Juniper Networks Junos OS results in a kernel crash, causing the device to restart, leading to a Denial of Service (DoS). Continued receipt and processing of this packet will create a sustained Denial of Service (DoS) condition. This issue only affects systems with IPv6 configured. Devices with only IPv4 configured are not vulnerable to this issue. This issue affects Juniper Networks Junos OS: 19.4 versions prior to 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S1, 20.2R2. This issue does not affect Juniper Networks Junos OS versions prior to 19.4R1.

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

Improper handling of exceptional conditions in IPv6 packet processing in Juniper Junos OS allows malformed IPv6 packets to trigger a kernel crash, causing device restart and sustained DoS. Only systems with IPv6 configured are vulnerable; IPv4-only systems are unaffected.

MitigationUpgrade to fixed Junos OS versions (19.4R3+, 20.1R2+, 20.2R1-S1/20.2R2+). If IPv6 is not required, disable IPv6 as an interim mitigation. Implement IPv6 packet filtering at network edges to block malformed packets.

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:= 19.4= 20.1= 20.2

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
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? 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 the installed Junos OS version
    Run the command 'show version' on the device CLI and note the exact Junos version string (for example, 19.4R1, 20.1R2, 20.2R3)
    Affected if The installed version is Junos 19.4 (any R release), 20.1 (any R release), or 20.2 (any R release) before the fixed releases (19.4R3+, 20.1R2+, 20.2R1-S1, or 20.2R2+)
  2. Verify IPv6 is configured on the system
    Run 'show interfaces' or 'show ipv6 interface' to list interfaces with IPv6 addresses assigned
    Affected if Any interface shows an IPv6 address or IPv6 is explicitly configured (including link-local only configurations)
  3. Confirm IPv6 protocol is enabled
    Run 'show configuration protocols ipv6' or check the base configuration for 'family inet6' under interfaces
    Affected if IPv6 protocol family is enabled on any interface or globally in the configuration

The device is affected only if it runs a vulnerable Junos version (19.4, 20.1, or 20.2 series before fixes) AND has IPv6 configured or enabled; IPv4-only deployments are not affected.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to fixed Junos OS versions (19.4R3+, 20.1R2+, 20.2R1-S1/20.2R2+). If IPv6 is not required, disable IPv6 as an interim mitigation. Implement IPv6 packet filtering at network edges to block malformed packets.

Recommended fix High confidence

19.4R3+, 20.1R2+, or 20.2R2 (depending on current branch)

  1. Check if IPv6 is configured on the device using 'show configuration protocols inet6' or 'show interfaces' - only IPv6-enabled devices are vulnerable
  2. Identify current Junos OS version using 'show version' command
  3. For 19.4 branch: upgrade to 19.4R3 or later
  4. For 20.1 branch: upgrade to 20.1R2 or later
  5. For 20.2 branch: upgrade to 20.2R2 (or 20.2R1-S1)
  6. Download the appropriate Junos OS release from Juniper Networks support portal
  7. Follow standard Junos upgrade procedure: validate software package, transfer to device, and reboot
  8. After upgrade, verify the device is running the fixed version with 'show version'
Caveat Standard Junos upgrade considerations apply - review release notes for compatibility, test in non-production environment first, plan maintenance window for reboot

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Scoped from the published advisory
  • Consultation6.0 h
  • Implementation4.0 h
  • Testing8.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,840
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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-2021-0299 in production — separate from our analysis above.

No notes yet

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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