CVE-2021-0299Network attack vector

Device restart via malformed IPv6 packet

Published Oct 19, 2021 · Updated Sep 16, 2024

Improper handling of exceptional conditions in Junos OS allows remote attackers to crash and restart IPv6-configured devices via malformed packets. The kernel mishandles a transit or directly received malformed IPv6 packet, enters a crash state, and reboots the device. Exploitation requires IPv6 configuration and continued packet delivery; IPv4-only devices are unaffected, and the consequence is sustained denial of service through repeated restarts.

CVSS severity7.5
High
EPSS probability1.01%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper handling of exceptional conditions in Junos OS allows remote attackers to crash and restart IPv6-configured devices via malformed packets. The kernel mishandles a transit or directly received malformed IPv6 packet, enters a crash state, and reboots the device. Exploitation requires IPv6 configuration and continued packet delivery; IPv4-only devices are unaffected, and the consequence is sustained denial of service through repeated restarts.

The record

CVE
CVE-2021-0299
Published
Oct 19, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-755, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=19.4 <19.4R3
  2. Affected versionversion=20.1 <20.1R2
  3. Affected versionversion=20.2 <20.2R1-S1, 20.2R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=19.4 <19.4R3; version=20.1 <20.1R2; version=20.2 <20.2R1-S1, 20.2R2

Published CVSS scores

7.1NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:C
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-755Improper Handling of Exceptional Conditions
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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